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Maksimchuk, P., A. Masalov, V. Seminko, and Yu Malyukin. "Formation of Luminescence Centers in Oxygen-Deficient Cerium Oxide Nanocrystals." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35446.
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In this work the peculiarities of oxygen vacancies formation in cerium oxide nanoparticles for different
external influences have been investigated by spectroscopic methods.
The features of oxygen vacancies and therefore non-stoichiometric cerium oxide formation in CeO2
nanocrystals depending on the atmosphere of high temperature treatment were investigated. Stimulation
of oxygen vacancies formation in reducing and neutral atmospheres was revealed. Occurrence of two different
luminescence centers (viz. the charge-transfer complexes formed by Ce4+ and O2- ions, and Ce3+ ions
stabilized by vacancies) after cerium oxide nanoparticles annealing in a neutral atmosphere has been observed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35446
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SARTORI, EMANUELA. "EMISSIVE NANOCRYSTALS FOR OPTOELECTRONIC APPLICATIONS." Doctoral thesis, Università degli studi di Genova, 2022. http://hdl.handle.net/11567/1074636.
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Metal halide perovskites (particularly doped perovskites and lead free double perovskites) are starting to generate great interest in the scientific community due to their unique electronic and structural properties, such as high photoluminescent quantum yields (PLQY, up to 90%), chemical diversity in terms of elements employed and tunable optical properties. Consequently, their application in optoelectronic devices gained attention. During these three years, I intensively worked on the synthesis and characterization of inorganic perovskites nanocrystals, starting from lead halide perovskites (LHPs) in 3D and 0D structure and then moving to the double perovskites (DPs). Generally, the aim of these studies is to replace Pb with less toxic elements, producing materials more stable to atmosphere conditions and with good optical properties. Thus, synthesis and optimization are the key words of this part of the work. Pb has been replaced with a monovalent (Ag, Na) and a trivalent (In, Bi), or a bivalent (Cu, Mn) and a trivalent (Sb) metal cation, leading to DPs (e.g. Cs2AgInCl6) and layered perovskites (e.g. Cs4CuSb2Cl12), respectively. However, perovskites are not the only promising candidate for optoelectronic devices, in particular considering the increasing interest in studying NIR emitting materials. In this field, my work on silicates takes place. In fact, Cu - based silicates (e.g. CaCuSi4O10) possess a high emission in NIR region (900–1000 nm). Moreover, their high Stokes shift, which limits re-absorbance phenomenon, and the high stability to ambient condition and sun irradiation, suggest their use in solar absorbing devices. During my PhD I performed deep structural investigation using synchrotron radiation after an optimization of the material synthesis; then, I worked on their exfoliation leading to the formation of very homogeneous nanosheets.
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Seminko, V. V., Yu V. Malyukin, and A. A. Masalov. "Spectroscopically detected segregation of Pr3+ ions in Y2SiO5 nanocrystals." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35434.
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Segregation of Pr3+ ions in Y2SiO5:Pr3+ nanocrystals was revealed by means of spectroscopic techniques.
Increase of doped ions concentration in the near-surface layer of Y2SiO5:Pr3+ nanocrystals was confirmed
by modification of luminescence spectra with the heat treatment temperature. Relaxation of excess elastic
stresses created by Pr3+ ions with volumes greater than volume of regular Y3+ ion was determined to be the
main cause of observed effects. Theoretical estimations clearly confirm the preliminary predictions.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35434
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Wilkinson, Andrew Richard. "The optical properties of silicon nanocrystals and the role of hydrogen passivation /." View thesis entry in Australian Digital Program, 2006. http://thesis.anu.edu.au/public/adt-ANU20060202.111537/index.html.
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Williams, Diane Keith. "Particle Size Dependence on the Luminescence Spectra of Eu3+:Y2O3 and Eu3+:CaO." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/29719.
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Since the Eu3+ ion can occupy different cation sites in a host material, it can serve as a useful probe of nanocrystalline structures to gain more insight into the structural changes that can occur when the particle size is reduced from the bulk to nanometer regime. The use of laser spectroscopy to probe two nanocrystalline structures, Eu3+:Y2O3 and Eu3+:CaO, was investigated. The nanocrystalline structures were prepared by the laser-vaporization-gas-phase condensation of the bulk oxides. The particle size distribution and dominant particle diameters of the nanocrystals were determined by transmission electron microscopy.
The particle size dependency results of Eu3+:Y2O3 revealed three distinct phases: (1) the sharp lines of the monoclinic Y2O3 were dominant in the larger particles; (2) the C2 site of the cubic phase, which appears in the smaller particles; and (3) the amorphous phase that increases in intensity as the particle size decreases. The observation of distinct spectral lines from the monoclinic phase confirms the presence of a crystalline phase for all of particle sizes studied.
The site-selective results of various concentrations of 13-nm Eu3+:CaO showed that the laser-vaporization-gas-phase condensation method of preparation produced two europium-containing phases at most concentrations: cubic CaO and monoclinic Eu2O3. Results showed that the monoclinic Eu2O3 phase could be reduced by 95% by annealing at 800 0C for 30 minutes without particle growth.
Since the Eu3+ ion and the Y3+ ion are isovalent, the substitution of a Eu3+ ion into Y2O3 is considered a trivial case of extrinsic disorder since the impurity is neutral relative to a perfect crystal1. As a result, it is not necessary to have any other defects present in the crystals to maintain charge neutrality. With Eu3+:CaO, the dopant and host cation charges are different and therefore the dopant distribution can be investigated by site-selective spectroscopy.
Since the experimental dopant distribution results for nanocrystalline Eu3+:CaO were inconclusive, a model to predict the theoretical change in the dopant distribution in Eu3+:CaO as a function of particle size was developed. The model predicts that the defect chemistry is affected when the particle size is approximately 50 nm and smaller.<br>Ph. D.
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Vezzoli, S. "EXPERIMENTAL STUDY OF NANOCRYSTALS AS SINGLE PHOTON SOURCES." Doctoral thesis, Università degli Studi di Milano, 2013. http://hdl.handle.net/2434/222688.
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Wet-chemically synthesized colloidal nanocrystals are promising single photon emitters at room temperature, due to the strong quantum confinement induced by the small dimensions. However, their applications have been so far limited by two main drawbacks: the blinking of their photo-luminescence and a non-polarized emission.
This manuscript is consecrated to the study of the optical properties of a particular type of colloidal nanocrystals, called dot-in-rod (DR), in which a spherical CdSe core is surrounded by a rod-like CdS shell.
We demonstrate for the first time a suppression of the blinking in thick shell DRs. In contrast to spherical nanocrystals, we show that it can be obtained while keeping a good quality of the single photon emission and a high degree of linear polarization.
A complete room-temperature characterization of the optical, and especially quantum optical, properties of DRs is provided for several geometrical parameters.
In particular, an original approach, based on an ensemble photoluminescence measurement, is developed to assess the quality of a sample of nanocrystals as single photon sources.
By studying single DRs in a confocal microscope, we analyze the influence of the core size and of the shell thickness and length on the photon anti-bunching, radiative lifetime and polarization of the emission.
This systematic study brings a contribution to the understanding of the interaction processes of the confined carriers in semiconductor nanocrystals. The interplay of radiative and non-radiative recombinations and, in particular, the role of the Auger effect in the photo-luminescence blinking and in the emission of non-classical light are deeply investigated.
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La, Rosa Marcello. "Development of luminescent semiconductor nanocrystals (Quantum Dots) for photoinduced applications." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0591/document.
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Cette thèse s’est focalisée sur le développement de nanocristaux semi-conducteurs luminescents, i.e. des boîtes quantiques (quantum dots, QDs), pour des applications photo-induites. Ces nanomatériaux possèdent des propriétés optiques très intéressantes qui dépendent de leur taille et sont prometteurs pour des applications dans divers domaines.Les QD sont généralement hydrophobes mais de nombreuses applications intéressantes requiert une compatibilité avec l'eau ou du moins avec un environnement polaire. Cela, nécessite donc un traitement post-synthétique afin de modifier leur solubilité.Au cours de cette thèse, une nouvelle méthode pour transférer les QDs d'un solvant apolaire vers un solvant polaire a été développée en les fonctionnalisant avec l'acide lipoïque, un tensioactif complexant.L'acide lipoïque est une molécule chirale générant donc un effet de dichroïsme induit qui a pu être étudier, ainsi que sa dépendance vis-à-vis la taille des nanocristaux.Un objectif clef de ces recherches était le développement de QDs présentant un transfert d'énergie électronique réversible (REET). Il s’agit d’un transfert d'énergie bidirectionnel entre les QDs photoexcités et des unités chromophores appropriées fixées sur leur surface, dont la conséquence la plus importante est l'allongement de la durée de vie de luminescence du QD.Enfin, un nouveau protocole pour le dépôt de QDs chargés sur un substrat vitreux localement polarisé a été développé en collaboration avec le Dr Marc Dussauze de l'Université de Bordeaux<br>This thesis focuses on the development of luminescent semiconductor nanocrystals quantum dots (QDs) for photoinduced applications. QDs are promising nanomaterials with size-dependent optical properties and are attractive for applications in several fields.However, QDs are commonly hydrophobic and many interesting applications require their compatibility with water or at least with a polar environment, meaning a post-synthetic treatment is required to confer a different solubility.During these studies, a new method for transferring QDs from an apolar solvent to another one polar has been successfully developed, by exploiting lipoic acid, as a versatile surface capping agent. Moreover, lipoic acid is a chiral molecule so a possible induced dichroism effect has been also investigated, as well as its dependence on the size of nanocrystals.A major aim of this research was the development of QDs exhibiting reversible electronic energy transfer (REET). Such a process is a bidirectional energy transfer between the photoexcited QDs and suitable chromophoric units attached on their surface, whose most important consequence is the elongation of the luminescence lifetime of the QD. Strong experimental evidence for REET and accompanying modifications of the photophysical properties has been obtained. Such a process to our knowledge has never been observed in QD-based systems.Finally, a novel protocol for depositing charged QDs on a locally polarized glassy substrate has been developed in collaboration with Dr. Marc Dussauze of the University of Bordeaux
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Schnabel, Manuel. "Silicon nanocrystals embedded in silicon carbide for tandem solar cell applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:da5bbb64-0bcd-4807-a9f3-4ff63a9ca98d.
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Tandem solar cells are potentially much more efficient than the silicon solar cells that currently dominate the market but require materials with different bandgaps. This thesis presents work on silicon nanocrystals (Si-NC) embedded in silicon carbide (SiC), which are expected to have a higher bandgap than bulk Si due to quantum confinement, with a view to using them in the top cell of a tandem cell. The strong photoluminescence (PL) of precursor films used to prepare Si-NC in SiC (Si-NC/SiC) was markedly reduced upon Si-NC formation due to simultaneous out-diffusion of hydrogen that passivated dangling bonds. This cannot be reversed by hydrogenation and leads to weak PL that is due to, and limited by, non-paramagnetic defects, with an estimated quantum yield of ≤5×10<sup>-7</sup>. Optical interference was identified as a substantial artefact and a method proposed to account for this. Majority carrier transport was found to be Ohmic at all temperatures for a wide range of samples. Hydrogenation decreases dangling bond density and increases conductivity up to 1000 times. The temperature-dependence of conductivity is best described by a combination of extended-state and variable-range hopping transport where the former takes place in the Si nanoclusters. Furthermore, n-type background doping by nitrogen and/or oxygen was identified. In the course of developing processing steps for Si-NC-based tandem cells, a capping layer was developed to prevent oxidation of Si-NC/SiC, and diffusion of boron and phosphorus in nanocrystalline SiC was found to occur via grain boundaries with an activation energy of 5.3±0.4 eV and 4.4±0.7 eV, respectively. Tandem cells with a Si-NC/SiC top cell and bulk Si bottom cell were prepared that exhibited open-circuit voltages V<sub>oc</sub> of 900 mV and short-circuit current densities of 0.85 mAcm<sup>-2</sup>. Performance was limited by photocurrent collection in the top cell; however, the V<sub>oc</sub> obtained demonstrates tandem cell functionality.
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Kumar, Upkar. "Plasmon logic gates designed by modal engineering of 2-dimensional crystalline metal cavities." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30170/document.
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L'objectif principal de cette thèse est de concevoir, fabriquer et caractériser les dispositifs plasmoniques basés sur les cavités métalliques bidimensionnelles monocristallines pour le transfert d'information et la réalisation d'opérations logiques. Les fonctionnalités ciblées émergent de l'ingénierie spatiale et spectrale de résonances plasmon d'ordre supérieur supportées par ces cavités prismatiques. Les nouveaux éléments étudiés dans cette thèse ouvrent la voie à de nouvelles stratégies de transfert et de traitement de l'information en optique intégrée et miniaturisée. Dans un premier temps, nous caractérisons la réponse optique des nanoplaquettes d'or ultra-fines et de taille submicronique (400 à 900 nm) par spectroscopie en champ sombre. La dispersion des résonances plasmoniques d'ordre supérieur de ces cavités est mesurée et comparée avec un bon accord aux simulations obtenues par la méthode des dyades de Green (GDM). En outre, nous présentons une analyse par décomposition lorentzienne des réponses spectrales de ces nanoprismes déposés sur des minces substrats métalliques. Nous avons, par ailleurs systématiquement étudié les effets qui pourraient modifier les résonances plasmoniques par microscopie de luminescence non-linéaire, qui s'est avérée un outil efficace pour observer la densité d'états locale des plasmons de surface (SPLDOS). En particulier, nous montrons que les caractéristiques spectrale et spatiale des résonances plasmoniques d'ordre supérieur peuvent être modulées par la modification du substrat (diélectrique ou métallique), par l'insertion contrôlée d'un défaut dans la cavité ou par le couplage électromagnétique, même faible, entre les deux cavités. L'ingénierie rationnelle de la répartition spatiale des résonances confinées 2D a été appliquée à la conception de dispositifs à transmittance accordable entre deux cavités connectées. Les géométries particulières sont produites par gravure au faisceau d'ions focalisé sur des plaquettes cristallines d'or. Les dispositifs sont caractérisés par cartographie de luminescence non-linéaire en microscopie confocale et en microscopie de fuites. Cette dernière méthode offre un moyen unique d'observer la propagation du signal plasmon dans la cavité. Nous démontrons la dépendance en polarisation de la transmission plasmonique dans les composants à symétrie et géométrie adéquates. Les résultats sont fidèlement reproduits par notre outil de simulation GDM adapté à la configuration de transmission. Enfin, notre approche est appliquée à la conception et à la fabrication d'une porte logique reconfigurable avec plusieurs entrées et sorties. Nous démontrons que dix des douze portes logiques possibles à 2 entrées et 1 sortie sont activable sur une même structure en choisissant les trois points d'entrée et de sortie et en ajustant le seuil de luminescence non-linéaire pour le signal de sortie<br>The main objective of this PhD work is to design, fabricate and characterize plasmonic devices based on highly crystalline metallic cavities for the two-dimensional information transfer and logic gate operations. First, we thoroughly characterize the optical response of ultra-thin gold colloidal cavities of sub-micronic size (400 to 900 nm) by dark- field spectroscopy (Fig. 1a). The dispersion of the high order plasmonic resonances of the cavities is measured and compared with a good agreement to simulations obtained with a numerical based on the Green Dyadic Method (GDM). We further extend our experiments to systematically tune the spectral responses of these colloidal nanoprisms in vicinity of metallic thin film substrates. A comprehensive study of these sub-micronic size cavity in bowtie antenna configuration is performed. We show a polarization-dependent field enhancement and a nanoscale field confinement at specific locations in these bowtie antennas. We systematically study the effects that could potentially affect the plasmonic resonances by non-linear photon luminescence microscopy, which has proved to be an efficient tool to observe the surface plasmon local density of states (SPLDOS). Inparticular, we show that an effective spatially and spectrally tuning of the high order plasmonic resonances can be achieved by the modification of the substrate (dielectric or metallic), by the controlled insertion of a defect inside a cavity or by the weak electromagnetic coupling between two adjacent cavities. The rational tailoring of the spatial distribution of the 2D confined resonances was applied to the design of devices with tunable plasmon transmittance between two connected cavities. The specific geometries are produced by focused ion milling crystalline gold platelets. The devices are characterized by non-linear luminescence mapping in confocal and leakage radiation microscopy techniques. The latter offers a unique way to observe propagating SPP signal over a 2D plasmonic cavity. We demonstrate the polarization-dependent mode-mediated transmittance for devices withadequate symmetry. The results are faithfully reproduced with our simulation tool based on Green dyadic method. Finally, we extend our approach to the design and fabrication of a reconfigurable logic gate device with multiple inputs and outputs. We demonstrate that 10 out of the possible 12 2-input 1-output logic gates can be implemented on the same structure by choosing the two input and the one output points. We also demonstrate reconfiguration of the device by changing polarization of the incident beam, set of input locations and threshold of the non-linear luminescence readout signal
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Eloi, Fabien. "Étude de la luminescence de nanocristaux semi-conducteurs couplés avec des structures plasmoniques à températures ambiante et cryogénique." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLV117/document.
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Les nanocristaux semi-conducteurs colloïdaux possèdent des propriétés photo-physiques qui en font des objets de choix pour des applications variées, comme le marquage biologique, le photovoltaïque ou encore l'optique quantique. Dans cette thèse, nous étudions les modifications, introduites par des réseaux d'or, de la fluorescence de nanocristaux CdSe/CdS à coquille épaisse. Nous présentons tout d'abord les propriétés fondamentales de ces nanocristaux de CdSe/CdS puis la manière dont leurs propriétés d'émission peuvent être contrôlées par l'environnement électromagnétique, en détaillant en particulier le cas d'un couplage avec des plasmons de surface. Des simulations réalisées par nos collaborateurs du LICB dans le cadre d'un projet ANR sont ensuite comparées à nos mesures expérimentales. Nous observons que le couplage des nano-émetteurs individuels au réseau d'or permet à la fois d'accélérer l'émission spontanée et de mieux la collecter. Les structures métalliques sont optimisées pour que les améliorations détectées soient peu sensibles à la position de l'émetteur. Un effet supplémentaire est le contrôle de la polarisation de l'émission qui se révèle être fixée pa r le réseau. Nous rapportons également des changements dans la statistique temporelle d'émission des photons et notamment la suppression totale du scintillement. Les métaux étant connus pour leurs pertes ohmiques, des expériences ont été réalisées pour montrer que les pertes non radiatives qu'elles entraînent peuvent être réduites à basse température. Nous avons examiné le cas d'une surface d'or plane ainsi que des réseaux linéaires et circulaires. Enfin, une nouvelle méthode de post-traitement a été développée en parallèle. Elle permet par exemple d'étudier les variations de l'efficacité quantique bi-excitonique dans des nanocristaux enrobés d'or suivant l'état de charge de l'émetteur<br>Colloidal semiconductor nanocrystals are fluorescent nano-objects exhibiting discrete energy levels which justify their second appellation: quantum dots (QDs). Due to their high efficiency and ease of use, they find potential applications in a wide range of fields. Their usefulness for biological labeling, optoelectronic components in flat screens, light harvesting or quantum optics has been demonstrated by many studies. In this thesis, we use gold gratings in order to modify the emission properties of CdSe/CdS core-shell nanocrystals. After a brief presentation of their electronic and fluorescence properties, we explain how those properties can be modified by the control of the electromagnetic environment with particular care to the case of surface plasmons. We then show through experiment and simulations that those plasmons enable better collection efficiency, faster photo-luminescence decay rates, and polarized emission without being particularly restricting towards QD positioning. Changes in the emission statistics are also observed, notably total suppression of the blinking in the fluorescence intensity. Further experiments at low temperature have been realized in order to assess the importance of the gold ohmic losses. We investigated the case of a flat gold film as well as linear and circular gratings. A new post-selection method is also introduced and used to study the variations of the bi-excitonic quantum yield for nanocrystals embedded in a gold nano-resonator as a function of the ionization state of the emitter
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Weimmerskirch, Jennifer. "Propriétés de luminescence et caractérisation structurale de films minces d'oxydes de silicium dopés au cérium et codopés cérium-ytterbium." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0180/document.
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Ce travail de thèse concerne l’élaboration et la caractérisation chimique et structurale de couches minces d’oxyde de silicium dopées avec des terres rares ainsi que l’étude de leurs propriétés de photoluminescence. Les films sont dopées avec du cérium. Le co-dopage cérium et ytterbium est également étudié dans le cas des couches de SiO2. Il est montré que dans les oxydes de composition SiO1, le cérium joue un rôle important dans la structure et l’organisation chimique de l’oxyde, notamment en favorisant la démixtion de l’oxyde. L’exposition à un faisceau laser focalisé engendre une démixtion locale favorisée par le cérium. Pour les films minces de SiO1,5 contenant à la fois du cérium et des nanocristaux de silicium, les différentes étapes de la séparation de phase entre nanocristaux de Si et agrégats riches en Ce ont été mises en évidence, notamment par sonde atomique tomographique et par microscopie électronique à balayage en transmission. Les propriétés de luminescence des dopants sont discutées en lien avec la microstructure de la matrice hôte. Pour tous ces systèmes, la formation d’un silicate de cérium de composition Ce2Si2O7 à haute température (> 1100°C) a été mise en évidence. Le cérium présent sous forme d’ions isolés ou dans un silicate émet intensément dans le bleu (400 nm) à température ambiante ce qui pourrait être intéressant pour le développement de diodes bleues en filière Si. Enfin, un transfert d’énergie des ions Ce3+ vers les ions Yb3+ a été mis en évidence dans les films minces de SiO2 ouvrant ainsi la voie à de possibles applications dans le domaine du solaire photovoltaïque<br>This thesis concerns the structural characterization and the photoluminescence properties of thin silicon oxide films doped with rare earths The films are doped with cerium. The co-doping with both cerium and ytterbium is also studied in the case of SiO 2 layers. It is shown that in oxides with composition SiO1, cerium plays an important role in the structure and chemical organization of the oxide, in particular by promoting phase separation of the oxide. The exposure to a focused laser beam generates a local demixtion favored by cerium. For thin SiO1,5 films containing both cerium and silicon nanocrystals, we are able to follow the phase separation occuring between Si nanocrystals and Ce rich aggregates using both atom probe tomography and scanning transmission electron microscopy. The luminescence properties of dopants are discussed in connection with the microstructure of the host matrix. For all these systems, the formation of a cerium silicate with composition Ce2Si2O7 is observed at high temperature (> 1100 ° C). The cerium present either as isolated Ce3+ ions or in a silicate emits intensely at 400 nm (blue) at room temperature, which might be of interest for the development of blue light emitting diodes fully compatible with the Si technology. Finally, an energy transfer from Ce3+ ions to Yb3+ ions is demonstrated in thin SiO2 films opening the route to possible applications in the field of photovoltaics
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Yahia, Ammar Akram. "Synthèse, caractérisations et fonctionnalisation de nanocristaux semi-conducteurs luminescents." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAF058/document.
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Nous avons développé plusieurs méthodes de synthèse de nanocristaux semi-conducteurs luminescents directement en solution aqueuse. Des nanoparticules de CdTexSy ont été préparées en phase aqueuse et les propriétés optiques ont été étudiées. Suite aux caractérisations chimiques, un modèle a été proposé pour calculer le poids moléculaire et déterminer la formule molaire des nanoparticules de CdTexSy. Nous avons démontré l’existence d’une relation entre le rendement quantique et le nombre de ligand à la surface des nanoparticules. Les propriétés optiques ont été améliorées grâce à la synthèse sous irradiation micro-ondes. Cette méthode de synthèse nous a permis de synthétiser des nanoparticules de CdTexSeySZ avec de bonnes propriétés à 680 nm. Les nanoparticules ont été couplées avec différentes molécules (Rouge du Nil, ligands Bispidines) et protéines (albumine de sérum bovin; BSA et anticorps; PSR 222). Le couplage a été mis en évidence par gel d’électrophorèse. Nous avons également testé les nanoparticules comme donneur ou accepteur dans des systèmes de transfert d’énergie<br>We have developed several methods for the synthesis of luminescent semiconductor nanocrystals in aqueous solution. CdTexSy nanoparticles were prepared in the aqueous solution and their optical properties have been studied. Following chemical characterization, a model was proposed to calculate the molecular weight and molecular formula CdTexSy of the nanoparticles. We have demonstrated the existence of a relationship between the quantum yield and the number of ligands at the surface of the nanoparticles. The optical properties have been improved by using microwave irradiation for the synthesis. This method has allowed us to synthesize CdTexSeySz nanoparticles with good optical up to 680 nm. The nanoparticles were then coupled with various molecules (Nil Red, Bispidins ligands) and proteins (bovin sérum albumin; BSA and antibody; PSR 222). The coupling was demonstrated by gel electrophoresis. We also tested the nanoparticles as a donor or acceptor in energy transfer systems
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Kork, El Nayla. "Near field optical spectroscopy of hybrid nanoparticles for biosensor application and confocal microscopy of single silicon nanocrystals." Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10108/document.
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Le domaine des nanomatériaux joue un rôle de plus en plus important dans de nombreuses applications, qu’elles soient de natures biologique, médicales électroniques etc… Dans ce travail, nous présenterons des résultats concernant deux types de nanoparticules, le premier genre traite de nanoparticules hybrides confectionnées chimiquement pour des fins biologiques, le deuxième concerne des nanocristaux de silicium fabriqués par pyrolise laser pour des applications potentielles en optoélectronique. Les études sont menées en mettant en œuvre deux différentes techniques optiques, l’une en champ lointain, l’autre en champ proche. Dans le cas des nanohybrides, nous nous intéresserons à une caractérisation par microscopie en champ proche, qu’elle soit de nature spectroscopique ou d’imagerie simple, en utilisant en particulier une configuration optique guidante. Nous ferons un premier point à propos de l’émission de ses nanoparticules, puis discuterons des problèmes d’artefacts et de la résolution des images que nous pouvons atteindre avec notre montage. Nous prouverons l’importance essentielle du rôle des nanohybrides en tant que marqueur biologiques, et ceci dans deux différentes types de configuration de capteurs biologiques. Les nanoparticules de silicium de petites tailles (< 3 nm) seront étudiées essentiellement par microscopie confocale. Plus précisément, nous nous intéressons aux différents procédés de luminescence qui ont lieu lors de l’excitation d’une nanoparticule unique, en tenant compte des effets de taille et de surface. Nous chercherons à étudier l’influence de l’environnement des nanoparticules sur leurs propriétés spectrales en les plaçant dans des couches minces de natures diélectriques différentes. Nous conclurons enfin sur une brève description des différents effets Sark qui prennent lieu dans un tel système<br>The domain of nanomatrials plays an important role in many biological, medical and electronic applications. In this work, we present results concerning two types of nanoparticles : the first kind treats with hybrid nanoparitcls chemically synthesized for biological means, the second concerns silicon nanocrystals fabricated by laser pyrolisis for optoelectronic applications. The studies are done by using two different optical techniques, one in the far field, the other in the near field. In the nanohybrids case, we are interested by spectroscopic, and imaging near field characterization, by particularly using a waveguide configuration. We will first shed light about the emission properties of such nanoparticles, and then discuss artefact problems, in addition to the resolution of the images we can attain in our setup. We will prove the essential importance of the role of nanohybrids as biological markers with two different types of biosensors. The small sized silicon nanoparticles (< 3 nm) are essentially studied by confocal microscopy. More precisely, we will be interested by the different luminescence processes taking place during the excitation of a unique nanoparticle, by taking into consideration the surface effects. We will search to study the influence of the nanoparticles environment on their spectral properties by placing them in thin films having different dielectric properties. We will conclude with a small description of the stark effects which take place in such a system
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Biteen, Julie Suzanne Heath James R. "Plasmon-enhanced silicon nanocrystal luminescence for optoelectronic applications /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-05312006-163455.
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Pringle, Todd Andrew. "Non-Thermal Plasma Synthesis of Luminescent Silicon Nanocrystals from Cylclohexasilane." Diss., North Dakota State University, 2019. https://hdl.handle.net/10365/31690.
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In this report we establish cyclohexasilane (CHS) as a reliable precursor for non-thermal plasma synthesis of high quality photoluminescent silicon nanocrystals (SiNCs). We demonstrate that this synthesis approach can produce high quality, size tunable silicon quantum dots with quantum yields exceeding 60% as synthesized (subsequent work in our group has measured over 70% quantum yield after density gradient ultracentrifugation size purification).After a brief background on non-thermal plasma synthesis, the characterization methods used in this study, and an overview of CHS, we report at length on our development of the apparatus used, and our exploration of the controllable processing parameters of the synthesis method. We describe our successes and challenges with size tuning, sample collection, and passivation. Finally, we discuss preliminary studies we performed to identify promising future research areas. Novel reactor designs, blue light passivation, and magnetic confinement of plasma are described briefly to entice future researchers.
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La, Rosa Marcello <1989>. "Development of Luminescent Semiconductor Nanocrystals (Quantum Dots) for Photoinduced Applications." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8059/1/LaRosa_Marcello_Tesi.pdf.
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This thesis focuses on the development of luminescent semiconductor nanocrystals quantum dots (QDs) for photoinduced applications. QDs are promising nanomaterials with size-dependent optical properties and are attractive for applications in several fields.
However, QDs are commonly hydrophobic and many interesting applications require their compatibility with water or at least with a polar environment, meaning a post-synthetic treatment is required to confer a different solubility.
During these studies, a new method for transferring QDs from an apolar solvent to another one polar has been successfully developed, by exploiting lipoic acid, as a versatile surface capping agent. Moreover lipoic acid is a chiral molecule so a possible induced dichroism effect, which has been investigated, as well as its dependence on the size of nanocrystals.
A major aim of this research was the development of QDs exhibiting reversible electronic energy transfer (REET). Such a process is a bidirectional energy transfer between the photoexcited QDs and suitable chromophoric units attached on their surface, where the most important consequence is the elongation of the luminescence lifetime of the QD. Strong experimental evidence for REET and accompanying modifications of the photophysical properties has been obtained. Such a process to our knowledge has never been observed in QD-based systems.
Finally, a novel protocol for depositing charged QDs on a locally polarized glassy substrate has been developed in collaboration with Dr. Marc Dussauze of the University of Bordeaux.
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Chen, Yue Ph D. Massachusetts Institute of Technology. "Syntheses of biocompatible luminescent nanocrystals for visible and short-wave infrared imaging applications." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115798.
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Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2018.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>The primary focus of this thesis is to synthesize biocompatible luminescent nanocrystals for visible and short-wave infrared (1-2 [mu]m, SWIR) imaging applications. Quantum dots (QDs) have been promising fluorescent probes for biomedical imaging due to their high quantum yield (QY), narrow photoluminescence spectra, and excellent photostability. However, challenges remain to be solved to transfer the as-synthesized hydrophobic QD to aqueous solutions while maintaining the high QY and a compact size. This study involves the design and synthesis of a novel ligand that can be introduced to the established QD synthesis, producing norbornene functionalized QDs that can be readily phase transferred into water via norbornene/tetrazine click chemistry, meanwhile allowing flexible functionalization of the QDs by incorporating a functional group on the hydrophilic chain. This ligand system can be applied to a variety of carboxylic-ligand-stabilized QDs, with emission spectra spanning the visible and the SWIR region. The resulting water-soluble QDs exhibit a high QY, a small hydrodynamic diameter (HD), and excellent colloidal stability and pH stability. Further in vitro cell labeling experiments using azido-functionalized QDs demonstrates their potential for cell targeting applications. As in vivo imaging in the SWIR range has further reduced background noise from tissue scattering compared to traditional visible and near infrared (0.7-1 tm, NIR) imaging, images of higher contrast and better resolution can be readily obtained. The next challenge is to develop SWIR emitters that have high quantum efficiency and minimal toxicity, which is of critical importance in order to promote this technology for clinical applications. Our study found that the emission of luminescent gold nanoclusters can be tuned from the visible to the SWIR region by proper selection of ligands and post ligand modifications. The SWIR-emitting gold nanoclusters have a good QY, a HD that is small enough that they exhibit a rapid renal clearance, and images taken in the SWIR region show better resolution of the blood vessels than in the NIR region.<br>by Yue Chen.<br>Ph. D. in Physical Chemistry
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CAPITANI, CHIARA. "Synthesis of semiconductor colloidal nanocrystals with large Stokes-shift for luminescent solar concentrators." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/366195.
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I concentratori solari luminescenti (LSCs) sono delle guide d’onda composti da una matrice polimerica drogata o ricoperta con fluorofori. La luce solare diretta e/o diffusa che penetra nella matrice è assorbita dai fluorofori e poi riemessa dagli stessi con energia minore. La luce emessa, grazie alla riflessione totale interna, propaga fino a raggiungere i bordi della guida d’onda dove è convertita in elettricità da celle fotovoltaiche poste sul perimetro della matrice.
L’efficienza del dispositivo è ridotta da numerosi processi di perdita, sia dovuti alla riflessione della matrice e al cono di fuga, sia quelli che dipendono dalle caratteristiche dei fluorofori, come il coefficiente di assorbimento, il quantum yield (QY) di fotoluminescenza (PL) e il riassorbimento.
Per minimizzare tali perdite, una buona alternativa ai tradizionali fluorofori sono i quantum dots (QDs) colloidali che presentano solitamente un elevato QY, un alto coefficiente di assorbimento e una lunghezza d’onda di emissione controllabile cambiando le dimensioni dei nanocristalli tramite modifiche dei parametri di sintesi. Inoltre, ingegnerizzando opportunamente i QDs, è possibile realizzare particelle con elevato Stokes-shift tra gli spettri di assorbimento ed emissione, in modo da ridurre quanto più possibile il riassorbimento.
Il progetto si è quindi focalizzato sullo sviluppo della sintesi di QDs, al fine di ottimizzare il QY di fotoluminescenza, la compatibilizzazione con la matrice polimerica e la fotostabilità, limitando comunque il riassorbimento.
Inoltre. la procedura di sintesi deve essere facilmente trasportabile su volumi industriali, per soddisfare il fabbisogno di produzioni di elevati metri quadrati di LSCs.
Durante i tre anni di progetto di dottorato in Alto Apprendistato ho potuto sviluppare una procedura di sintesi che consiste in quattro step:
• crescita di nanocristalli di CuInS2 core;
• formazione del quaternario tramite aggiunta di zinco (ZnCuInS2); passaggio cruciale per aumentare il QY e controllare la lunghezza d’onda di emissione;
• crescita di una shell di solfuro di zinco (ZnCuINS2/ZnS) per passivare la superficie dei nanocristalli, aumentare il QY e la fotostabilità;
• trattamento post sintesi di scambio di leganti parziale per migliorare la solubilità nella matrice polimerica.
I nanocristalli così prodotti mostrano un QY del 60% ed un’ottima solubilità nella matrice polimerica. Infatti, è stato prodotto un LSC di grande dimensione (30 cm x 30 cm x 0.7 cm) la cui optical power efficiency, OPE = 6.8%.
Inizialmente ho sviluppato la procedura di sintesi in un pallone di vetro da 25 mL, producendo 250 mg a sintesi. Grazie all’attrezzatura fornita da Glass to Power S.p.A ho potuto studiare lo scale-up della sintesi. Dapprima ho effettuato studi preliminare, per approfondire alcune possibili problematiche dovute all’aumento dei volumi, su palloni di maggiori dimensioni, 500 mL e 2 L. Analizzate e risolte le tematiche di riscaldamento e stop della sintesi ho effettuato sintesi in un reattore preindustriale producendo 300 g di nanocristalli di ZnCuINS2/ZnS.
Oltre ad incrementare la produzione di sintesi da 250 mg a 300 g mi sono occupata dell’ottimizzazione della procedura di sintesi. Ho testato diverse strategie per incrementare il QY senza danneggiare la solubilità nel polimero. Grazie ad una variazione di reagente nel secondo step e ad un incremento dei layer della shell ho ottenuto nanocristalli con 80% di QY.
Il prossimo step sarà effettuare lo scale-up di questa nuova procedura e produrre LSC di grandi dimensioni.
Grazie alle collaborazioni con altri studenti di dottorato ho sintetizzato nanocristalli di calcogenuro drogati oro e opportunamente decorati con molecole coniugate per sistemi di up-conversion. Grazie all’introduzione dell’oro in questi sistemi si è ottenuta un’efficienza di up-conversion del 12%.<br>Luminescent solar concentrators (LSCs) are waveguides composed of a polymeric matrix doped or coated with fluorophores. The direct and/or diffuse sunlight that penetrates the matrix is absorbed by the fluorophores and then re-emitted by them with less energy. The light emitted, thanks to the total internal reflection, propagates until it reaches the edges of the wave guide where it is converted into electricity by photovoltaic cells placed on the perimeter of the matrix.
The efficiency of the device is reduced by numerous loss processes, due to the reflection of the matrix and the escape cone, and/or due to the characteristics of the fluorophores, such as the absorption coefficient, the quantum yield (QY) of photoluminescence (PL) and the reabsorption.
To minimize losses due to fluorophores, a good alternative are colloidal quantum dots (QDs) that usually have a high QY, a high absorption coefficient and a controllable emission wavelength by changing the size of the nanocrystals. Furthermore, by properly engineering the QDs, it is possible to realize particles with high Stokes-shift between the absorption and emission spectra, in order to reduce the reabsorption as much as possible.
The project is focused on the development of the synthesis of QDs, in order to optimize the QY of photoluminescence, compatibility with the polymer matrix and photostability, while limiting the reabsorption.
Besides. the synthesis procedure must be easily transferable on industrial volumes, to meet the production needs of high square meters of LSCs.
During the three years of the doctoral project in High Apprenticeship I was able to develop a synthesis procedure consisting of four steps:
• growth of CuInS2 core nanocrystals;
• quaternary formation with zinc addition (ZnCuInS2); crucial step to increase the QY and control the emission wavelength;
• growth of a zinc sulphide shell (ZnCuInS2/ZnS) to passivate the surface of nanocrystals, increase QY and photostability;
• post-synthesis treatment of the partial exchange of ligands to improve solubility in the polymer matrix.
The nanocrystals thus produced show 60% QY and excellent solubility in the polymer matrix. In fact, a large size LSC (30 cm x 30 cm x 0.7 cm) was produced, whose optical power efficiency, OPE = 6.8%.
Initially, I developed the synthesis procedure in a 25 ml glass flask, producing 250 mg for batch. Thanks to the equipment provided by Glass to Power s.p.A I was able to study the increase in the scale of the synthesis. Firstly, in order to investigate some possible problems due to the increase in volumes, I have carried out preliminary studies on larger balloons, 500 mL and 2 L. After analysis of heating and quenching of synthesis, I have performed the synthesis in a preindustrial reactor producing 300 g of nanocrystals of ZnCuInS2/ZnS.
In addition I also optimized the synthesis procedure. I tested several strategies to increase QY without damaging solubility in the polymer. Thanks to a variation of the reagent in the second step and an increase of the shell layers, I obtained nanocrystals with 80% of QY.
The next step will be to scale up this new procedure and produce large LSCs.
I collaborated with other PhD students, in particular, I synthesized with a heat-up method CdSe nanocrystals doped with Au7 clusters and decorated with conjugated dyes as efficient triplet sensitizers or up-conversion applications (gold doping improves up-conversion efficiency). The beneficial effects of the doping strategy result in a maximum UC efficiency of 12%, which is an unprecedented result for up-conversion based on decorated NCs as triplet sensitizers.
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Morselli, Giacomo <1994>. "Synthesis and electronic properties of luminescent silicon nanocrystals and copper indium sulphide quantum dots." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10175/1/Thesis_Morselli%20G.pdf.
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In the last decades, nanomaterials, and in particular semiconducting nanoparticles (or quantum dots), have gained increasing attention due to their controllable optical properties and potential applications.
Silicon nanoparticles (also called silicon nanocrystals, SiNCs) have been extensively studied in the last years, due to their physical and chemical properties which render them a valid alternative to conventional quantum dots. During my PhD studies I have planned new synthetical routes to obtain SiNCs functionalised with molecules which could ameliorate the properties of the nanoparticle. However, this was certainly challenging, because SiNCs are very susceptible to many reagents and conditions that are often used in organic synthesis. They can be irreversibly quenched in the presence of alkalis, they can be damaged in the presence of oxidants, they can modify their optical properties in the presence of many nitrogen-containing compounds, metal complexes or simple organic molecules. If their surface is not well-passivated, the oxygen can introduce defect states, or they can aggregate and precipitate in several solvents.
Therefore, I was able to functionalise SiNCs with different ligands: chromophores, amines, carboxylic acids, poly(ethylene)glycol, even ameliorating functionalisation strategies that already existed.
This thesis will collect the experimental procedures used to synthesize silicon nanocrystals, the strategies adopted to functionalise effectively the nanoparticle with different types of organic molecules, and the characterisation of their surface, physical properties and luminescence (mostly photogenerated, but also electrochemigenerated).
I also spent a period of 7 months in Leeds (UK), where I managed to learn how to synthesize other cadmium-free quantum dots made of copper, indium and sulphur (CIS QDs). During my last year of PhD, I focused on their functionalisation by ligand exchange techniques, yielding the first example of light-harvesting antenna based on those quantum dots. Part of this thesis is dedicated to them.
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Levchuk, Ievgen [Verfasser], Christoph [Gutachter] Brabec, and Rainer [Gutachter] Hock. "Design and optimization of luminescent semiconductor nanocrystals for optoelectronic applications / Ievgen Levchuk ; Gutachter: Christoph Brabec, Rainer Hock." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1139171550/34.
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Talapin, Dmitri V. "Experimental and theoretical studies on the formation of highly luminescent II-VI, III-V and core shell semiconductor nanocrystals." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964732297.
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Debieu, Olivier [Verfasser], Friedrich [Akademischer Betreuer] Huisken, Rob [Akademischer Betreuer] Elliman, and Blas [Akademischer Betreuer] Garrido. "Optical characterization of luminescent silicon nanocrystals embedded in glass matrices / Olivier Debieu. Gutachter: Friedrich Huisken ; Rob Elliman ; Blas Garrido." Jena : Thüringer Universitäts- und Landesbibliothek Jena, 2012. http://d-nb.info/101996958X/34.
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López, Vidrier Julià. "Silicon Nanocrystal Superlattices for Light-Emitting and Photovoltaic Devices." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/334396.
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During the last decades, silicon nanocrystals have focused great attention due to the size-dependent physical properties they present, attributed to the quantum confinement effect. This, added to the bulk silicon compatibility with the well-established microelectronics technology and the low mining and manipulation costs this material presents, makes silicon a potential candidate for the growing photonics and optoelectronics fields. In particular, the tunnability of the electronic properties of silicon nanocrystals can be reached by controlling the nanocrystal size. This has been recently achieved by means of the superlattice approach, consisting of the alternated deposition of ultra-thin (2-4 nm) stoichiometric and silicon-rich layers of a given silicon-rich material. After a high-temperature annealing treatment, the silicon excess precipitates and crystallizes in the final form of nanocrystals, whose properties strongly depend on the fabrication process. Consequently, an ordered arrange of size-controlled nanocrystals (the superlattice) is obtained.
In this Thesis Project, the structural, optical, electrical and electro-optical properties of silicon nanocrystal superlattices have been studied, using two different silicon-based materials as host matrices: silicon oxide and silicon carbide. The fabrication of these material systems has been carried out at different European institutions, specialists in the controlled deposition of nm¬thick films. Aiming at the nanocrystal superlattices characterization, different experimental techniques have been employed, which yield structural (transmission and scanning electron microscopies, X-ray diffraction), optical (optical absorption, photoluminescence and Raman scattering spectroscopies) and electrical / electro-optical (current versus voltage analysis in dark and under illumination, and electroluminescence, electro-optical response and light-beam induced photocurrent spectroscopies) information.
From the material's point of view, the optimum structural properties that allow an almost perfect nanocrystal arrangement, size control and crystalline degree have been determined, always aiming at an optimum light emission and/or light absorption. Within this frame, fundamental studies have been performed to assess the crystalline degree of the nanostructures (confirming an atomic-thin transition layer between the crystalline nanocrystal core and the surrounding matrix), and to carefully inspect the controversial origin of luminescence within the nanocrystals when embedded in a silicon oxide matrix; as well, the structural conditions under which size-confinement of nanocrystals is reached when embedded in silicon carbide are reported. Once the best structural and optical properties from silicon nanocrystal superlattices were found, these material systems have been employed as active layers for light emitting and light converter (i.e. photovoltaic) devices. In oxide-based systems, the mechanisms that govern charge transport through the superlattices have been studied, and impact ionization has been hypothesized as the main electroluminescence excitation mechanism according to the experimental observations. In addition, the structural conditions (sublayer thicknesses, silicon-rich layer stoichiometry) that yield a maximum electroluminescence efficiency have been determined. Regarding silicon nanocrystals embedded in silicon carbide, a correlation has been established between the charge photogeneration and extraction when acting as an absorber material, which allowed assessing the structural conditions that maximize charge transport while minimizing the non-desirable recombination. Finally, via spectral response measurements, quantum confinement of excitons within silicon nanocrystals has been reported in silicon carbide matrix for the first time.
In conclusion, the study on silicon nanocrystal superlattices developed within the present Thesis Project reveals the potential of silicon oxide as host matrix for silicon nanostructures to be used as light-emitting devices; instead, silicon carbide has proved a more suitable host material for photovoltaic applications, which sheds light to the future application of silicon nanocrystals as the top cell of an all-Si tandem cell.<br>Els nanocristalls de silici han esdevingut objecte d'estudi durant l'últim quart de segle, degut a què presenten, a causa de l'efecte de confinament quàntic, unes propietats físiques dependents de la seva mida. A més, la compatibilitat del silici massiu amb la ben establerta tecnologia microelectrònica juga en favor de la seva utilització i el seu desenvolupament per a futures aplicacions en el camp de la fotònica i l'optoelectrónica. El control del creixement de nanocristalls de silici es pot dur a terme mitjançant el dipòsit de superxarxes d'entre 2 i 4 nm de gruix, on capes de material estequiomètric basat en silici s'alternen amb altres de material ric en silici. Un posterior procés de recuit a alta temperatura permet la precipitació de l'excés de silici i la seva cristal.lització, tot originant una xarxa ordenada de nanocristalls de silici de mida controlada.
En aquesta Tesi, s'han estudiat les propietats estructurals, òptiques, elèctriques i electro-òptiques de superxarxes de nanocristalls de silici embeguts en dues matrius diferents: òxid de silici i carbur de silici. Amb tal objectiu, s'han emprat tot un seguit de tècniques experimentals, que comprenen la caracterització estructural (microscòpia electrònica de transmissió i d'escombrat, difracció de raigs X), òptica (espectroscòpies d'absorció òptica, de fotoluminescència i dispersió Raman) i elèctrica / electro-òptica (caracterització intensitat-voltatge en foscor o sota il.luminació, electroluminescència, resposta electro-òptica), entre d'altres.
Des del punt de vista del material, s'han estudiat les propietats estructurals òptimes per tal d'obtenir un perfecte ordenament en la xarxa de nanocristalls, una major qualitat cristal.lina i unes propietats d'emissió òptimes. L'optimització del material s'ha dut a terme en vistes a la seva utilització com a capa activa dins de dispositius emissors de llum i fotovoltaics, l'eficiència dels quals ha estat monitoritzada segons els diferents paràmetres estructurals (gruix de les capes nanomètriques involucrades, estequiometria, temperatura de recuit). Finalment, els nanocristalls de silici embeguts en òxid de silici han demostrat un major rendiment com a emissors de llum, mentre que una matriu de carbur de silici beneficia les propietats d'absorció i extracció (fotovoltaiques) del sistema.
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Steveler, Émilie. "Etude des mécanismes de photoluminescence dans les nitrures et oxydes de silicium dopés aux terres rares (Er, Nd)." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0109/document.
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Ce travail de thèse est dédié à l'étude des transitions radiatives dans les matériaux de nitrure et d'oxyde de silicium dopés aux ions de terres rares (Er3+, Nd3+). La caractérisation optique des films minces élaborés par évaporation thermique est basée sur la spectroscopie de photoluminescence. Les études menées s'inscrivent dans la recherche de processus d'excitation indirecte des ions Er3+ et Nd3+ dans des matrices à base de silicium. Dans les nitrures et oxynitrures de silicium, un processus de transfert d'énergie permettant l'excitation indirecte des ions Er3+ est mis en évidence. Pour les couches minces amorphes, le couplage est attribué à des états électroniques localisés dans la bande interdite de la matrice. Pour les films recuits à haute température, les nanocristaux de silicium (nc-Si) jouent un rôle majeur dans l'excitation indirecte de l'erbium. Dans les matrices d'oxyde de silicium, l'existence de processus d'excitations directe et indirecte des ions Nd3+ est démontrée. Pour les films amorphes, l'excitation indirecte du Nd se fait via des états électroniques localisés dans la bande interdite de la matrice. Pour les films recuits au-delà de 1000 °C, les nc-Si jouent le rôle de sensibilisateurs pour les ions Nd3+. Les résultats suggèrent que l'excitation indirecte des ions Nd3+ grâce aux états localisés dans la bande interdite de la matrice pourrait être plus efficace que l'excitation via les nc-Si<br>This thesis is devoted to the study of radiative transitions in rare-earth (Er, Nd) doped silicon oxide and silicon nitride thin films. The optical characterization of thin films prepared by thermal evaporation is based on photoluminescence spectroscopy. In this work, we investigate indirect excitation processes of Er3+ and Nd3+ ions in silicon based materials. In silicon nitride and silicon oxinitride, an energy transfer leading to the indirect excitation of Er3+ ions is demonstrated. For amorphous samples, the sensitization of Er3+ ions is attributed to localized electronic states in the matrix bandgap. For samples annealed at high temperature, silicon nanocrystals play a major role in the indirect excitation of erbium. In silicon oxide thin films, we evidences that both direct and indirect excitation processes of Nd3+ ions occur. For amorphous samples, indirect excitation occurs thanks to localized electronic states in the matrix bandgap. For samples annealed at temperatures above 1000 °C, silicon nanocrystals are sensitizers of Nd3+ ions. Results suggest that indirect excitation thank to localized states in the matrix bandgap could be more efficient than indirect excitation thanks to silicon nanocrystals
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Grün, Mathias. "Les nanocristaux de silicium comme source de lumière : analyse optique et réalisation de microcavités." Thesis, Nancy 1, 2010. http://www.theses.fr/2010NAN10108/document.
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Ce travail de thèse concerne la réalisation et l'analyse des propriétés optiques de nanocristaux de silicium. Ces objets de taille nanométrique possèdent des propriétés optiques remarquables, en particulier de photoluminescence. Les propriétés de confinement quantique qui les caractérisent permettent d'obtenir un signal de luminescence intense dans le domaine du visible. Des composants optoélectroniques et photoniques ont été envisagés à base de nanocristaux de silicium. Les raisons physiques du fort signal de luminescence en revanche sont encore mal comprises. Les nanocristaux de silicium sont élaborés par évaporation. L'élaboration et le recuit thermique de multicouches SiO/SiO2 permet d'obtenir des nanocristaux de silicium de diamètre moyen bien contrôlé. Ceux-ci sont issus de la démixtion de la couche de SiO selon la réaction SiOx --> Si + SiO2. Le contrôle du diamètre des nanocristaux de silicium permet de maîtriser la région spectrale de luminescence dans la région du visible.La première partie de ce travail de thèse vise à isoler un ou quelques nanocristaux de silicium. L'objectif est de remonter à la largeur homogène de ces nano-objets. Dans un premier temps, une étude centrée sur le matériau SiOx est réalisée afin de réduire la densité surfacique de nanocristaux de silicium. Dans un deuxième temps, des moyens de lithographie ultime sont mis en oeuvre afin de réaliser des masques percés de trous de diamètres de l'ordre de la centaine de nanomètre. Des expériences de spectroscopie optique sont réalisées sur ces systèmes.La deuxième partie de ce travail vise à contrôler l'émission spontanée de lumière issue des nanocristaux de silicium. Ceci se fait en couplant les modes électroniques aux modes optiques confinés d'une microcavité optique. Le manuscrit détaille les moyens développés afin d'obtenir une microcavité optique dont les modes optiques puissent se coupler efficacement aux nanocristaux de silicium. Les propriétés optiques de ces systèmes sont finalement analysées<br>This work concerns the implementation and analysis of optical properties of silicon nanocrystals. These nanoscaled objects have remarkable optical properties, especially in photoluminescence. The properties of quantum confinement that characterize them allow obtaining an intense luminescence signal in the visible range. Optoelectronic and photonic devices have been proposed based on silicon nanocrystals. The physical reasons of the strong luminescence signal, however, are still poorly understood. The silicon nanocrystals are prepared by evaporation. The preparation and thermal annealing of multilayers SiO/SiO2 leads to silicon nanocrystals with a well controlled average diameter. They are created during the demixing of the SiO layer by the reaction SiO ? Si + SiO2. The control the diameter of the silicon nanocrystals influences directly the spectral region of luminescence in the visible region.The aim of first part of this work is to isolate one or a few silicon nanocrystals. The intent is to trace the homogeneous width of these nano-objects. Initially, a study focusing on the SiOx material is conducted to reduce the surface density of silicon nanocrystals. In a second step, lithography is implemented to make masks with holes with diameters of about one hundred nanometers. Optical spectroscopy experiments were performed on these systems.The second part of this work aims controlling the spontaneous emission of light from silicon nanocrystals. This is done by coupling the electronic transmission to optical modes confined in an optical microcavity. The manuscript describes the methods developed to obtain an optical microcavity whose optical modes can be coupled effectively to the silicon nanocrystals. The optical properties of these systems are finally analyzed
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Chang, Tung-Wah Frederick. "Luminescence and energy transfer excitation of infrared colloidal semiconductor nanocrystals /." 2006. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=442439&T=F.
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Cheylan, Stephanie. "Optical properties of silicon nanocrystals." Phd thesis, 2001. http://hdl.handle.net/1885/144961.
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Chang, Chia-Wei, and 張家瑋. "Down- and Up-converted Visible Luminescence Properties of Er3+-doped Y2Ti2O7 Nanocrystals." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/80944779317381649090.
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碩士<br>國立中正大學<br>光機電整合工程所<br>97<br>Er3+-doped Y2Ti2O7 thin films with the thickness of ~375 nm thin films were fabricated by the sol-gel spin-coating method. A pyrochlore phase ErxY2-xTi2O7 was observed with a strong (222) preferred orientation while the annealing temperature exceeded 800 °C. Below 800 °C annealing, thin films exhibited amorphous structure. The average visible transmittance calculated in the wavelength range 200–1100 nm of the Er3+-doped Y2Ti2O7 thin films annealed at 400 to 900 °C reduced from ~87 to ~77% because of the increase of grain size and surface roughness. The variation of refractive indexes and optical band gaps of Er3+-doped Y2Ti2O7 thin films strongly depend on the Er3+ concentrations and annealing temperatures. Higher annealing temperatures result in the increase of refractive indexes but the decease of optical band gaps. In addition, higher Er3+ concentrations lead to a decrease in both refractive indexes and optical band gaps. The variation of these basic optical properties can be attributed to the evolution of grain size, crystallinity, lattice constant, and composition of Er3+-doped Y2Ti2O7 thin films. Because the competition between the [OH-], concentration quenching effect, as well as the diversity and symmetry of Er3+ lattice sites, the Er3+ (5%)-doped Y2Ti2O7 thin films annealed at 700 °C for 1 h possessed the largest intensity of ~1.5μm PL and FWHM ~ 60 nm.
Er3+-doped Y2Ti2O7 nanocrystals with pyrochlore phase were fabricated by the Pechini sol-gel method and the average crystal size increased from ~34 to ~46 nm under 800 to 1000 °C/1 h annealing. The amorphous Er3+-doped Y2Ti2O7 nanocrystals was obtained at ≦700°C annealing temperature. The Er3+-doped Y2Ti2O7 nanocrystals possess the dual down- and up-converted luminescent properties, which convert the 380 and 980 nm photons to the visible green light (~526, and ~547 nm; 2H11/2→4I15/2 and 4S3/2→4I15/2) and red light (~660 nm; 4F9/2→4I15/2). For both high (10 mol%) and low (5 mol%) Er3+ doped concentration, the mechanism of up-converted green light is two-photon excited-state absorption; however, much stronger intensity of red light relative to green light is observed for sample with high Er3+ doped concentration (10 mol%), attributed to the reduced distance between Er3+-Er3+ ions resulting in the enhancement of the energy-transfer up-conversion and energy-transfer cross-relaxation mechanisms.
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Chiu, Yi-Shan, and 邱意珊. "A study on preparation and luminescence properties of Er3+-doped Y2Ti2O7 nanocrystals." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/23018698376874802380.
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碩士<br>國立中正大學<br>光機電整合工程所<br>98<br>Er3+-doped Y2Ti2O7 nanocrystals were fabricated by the sol-gel method. While the annealing temperature exceeds 757 °C, amorphous pyrochlore phase Er3+-doped Y2Ti2O7 transfers to well-crystallized nanocrystals, and the average crystal size increases from ~70 to ~180 nm under 800 to 1000 °C/1 h annealing. The Er3+-doped Y2Ti2O7 nanocrystals absorbing the 980 nm photons can produce the up-conversion (526, 547, and 660 nm; 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2, respectively) and Stokes luminescence (1528 nm; 4I13/2→4I15/2).
The IR PL decay curve is single-exponential for Er3+ (5 mol%)-doped Y2Ti2O7 nanocrystals but slightly nonexponential for Er3+ (10 mol%)-doped Y2Ti2O7 nanocrystals. For both 5 and 10 mol% Er3+ doping concentrations, the mechanism of up-converted green light is the two-photon excited-state absorption; however, much stronger intensity of red light relative to green light was observed for sample with 10 mol% Er3+ doping concentration. This phenomenon can be attributed to the reduced distance between Er3+-Er3+ ions, resulting in the enhancement of the energy-transfer up-conversion and cross-relaxation mechanisms.
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Chien, Yungchuan, and 簡勇全. "Up and Down-converted visible luminescence properties of Er3+ doped Gd2Ti2O7 nanocrystals." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/34303679092975627005.
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碩士<br>國立中正大學<br>光機電整合工程研究所<br>100<br>Er3+-doped Gd2Ti2O7 nanocrystals were fabricated by the sol-gel method. While the annealing temperature exceeds 800 °C, amorphous pyrochlore phase Er3+-doped Gd2Ti2O7 transfers to well-crystallized nanocrystals, and the average crystal size increases from ~70 to ~180 nm under 800 to 1200 °C/1 h annealing. The Er3+-doped Gd2Ti2O7 nanocrystals absorbing the 980 nm photons can produce the up-conversion (526, 547, and 660 nm; 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2, respectively) and Stokes luminescence (1528 nm; 4I13/2→4I15/2).
The IR PL decay curve is single-exponential for Er3+ (5 mol%)-doped Gd2Ti2O7 nanocrystals but slightly nonexponential for Er3+ (10 mol%)-doped Gd2Ti2O7 nanocrystals. For both 5 and 10 mol% Er3+ doping concentrations, the mechanism of up-converted green light is the two-photon excited-state absorption; however, much stronger intensity of red light relative to green light was observed for sample with 10 mol% Er3+ doping concentration. This phenomenon can be attributed to the reduced distance between Er3+-Er3+ ions, resulting in the enhancement of the energy-transfer up-conversion and cross-relaxation mechanisms.
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Vetrone, Fiorenzo. "Luminescence spectroscopy of Er³⁺ doped inorganic nanocrystals : an investigation into their upconversion properties." Thesis, 2005. http://spectrum.library.concordia.ca/8450/1/NR04038.pdf.
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This thesis presents a detailed investigation into the spectroscopic properties of inorganic nanocrystals doped with trivalent rare earth ions. We focus on their upconversion luminescence, emission of radiation at higher energy than the pump wavelength, and evaluate the fundamental mechanisms of upconversion in the nanocrystal. We evaluate the spectroscopic properties of sesquioxide nanocrystals doped with trivalent erbium (M 2 O 3 :Er 3+ , where M = Y, Lu, or Sc) prepared by the propellant synthesis technique. Characteristic green, red, and near-infrared Er 3+ emission is observed following excitation with 488 nm in all samples under investigation. The overall luminescence intensity of the sesquioxide nanocrystals is lower compared to the microcrystalline material (bulk) as a result of the presence of high vibrational energies, 1500 and 3350 cm -1 , due to adsorbed CO 3 2- and OH - anions, respectively, which significantly increase the rate of multiphonon relaxation. The garnet (Gd 3 Ga 5 O 12 :Er 3+ ) nanocrystals, however, have considerably less surface adsorbed species, which consequently increases the luminescence intensity drastically. The upconversion of red (n exc = 650 nm) and near-infrared (n exc = 800 or 980 nm) radiation into UV, blue, green, and red emission is studied for Er 3+ ions doped in various sesquioxide (Y 2 O 3 , Lu 2 O 3 , and SC 2 O 3 ) and garnet (Gd 3 Ga 5 O 12 ) nanocrystals over a wide range of temperatures and dopant concentration is investigated. We present, for the first time, upconversion in a trivalent rare earth (RE 3+ ) doped nanocrystalline material, specifically Y 2 O 3 :Er 3+ . We show that replacing the Y 3+ cation has significant consequences on the upconversion. The upconverted luminescence of Lu 2 O 3 :Er 3+ nanocrystals have intensities that are 100x greater compared to identically doped nanocrystalline Y 2 O 3 :Er 3+ . Furthermore, Sc 2 O 3:Er 3+ nanocrystals show an enhanced red emission, which is greater than Y 2 O 3 :Er 3+ nanocrystals (with identical Er 3+ concentration) due to the smaller unit cell resulting in increased interaction between Er 3+ ions. The upconversion is observed to be dependent on the method of preparation. We explore nanocrystalline Y 2 O 3 :Er 3+ prepared via the propellant synthesis technique and a controlled hydrolysis synthesis (or wet chemical synthesis) where we observed quite diverse upconversion behavior attributed to the vastly different morphological properties of the two different nanocrystalline materials. Additionally, we investigate the effect of Yb 3+ co-doping on the upconversion luminescence of Y 2 O 3 :Er 3+ nanocrystals prepared via the two distinct synthesis routes, and observe a significant change in the mechanisms of upconversion. In the sesquioxides, the upconversion properties of the nanocrystalline material are diverse from the bulk counterpart. Finally, we attempt to ascertain if any spectroscopic changes occur in nanosized Lu 2 O 3 :Nd 3+ , Y 2 O 3 :Sm 3+ and Y 2 O 3 :Dy 3+ prepared via combustion synthesis. In all cases, the size of the particles affects the luminescence behavior
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Lin, Guang Chun, and 林廣春. "Up-converted Visible Luminescence Properties of Er3+ and Yb3+ Co-doped Y2Ti2O7 Nanocrystals." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/40667102353356229108.
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碩士<br>國立中正大學<br>光機電整合工程研究所<br>99<br>The (Er3+, Yb3+)-codoped Y2Ti2O7 nanocrystals were synthesized by the sol-gel method in this work. We were focused on the fluorescent properties of different annealing temperature and different dopent concentrations of ytterbium ions.
Er3+ (5%) & Yb3+ (5, 10, 15, 20%)-codoped Y2Ti2O7 nanocrystals with particle size of 50~120 nm were synthesized by the sol-gel method. The strong green band centered at 547 nm (4S3/2 → 4I15/2) and red band centered at 678 nm (4F9/2 → 4I15/2) visiable emission and weak blue band centered at 409 nm (2H9/2 → 4I15/2) emission were observed in codoped nanoparticles under the 980 nm laser diode excitation.
The intensity of red band and blue band were increasing by concentration of ytterbium, but the intensity of green was decreased. The sample of (Er3+ 5%, Yb3+ 5%)-codoped Y2Ti2O7 nanocrystals have the best of brightness under 1000 ℃ annealing by photoluminescence spectroscopy measurement. The longest life time (1010 μs) at red band (678 nm) was observed in (Er3+5%, Yb3+5%)-codoped Y2Ti2O7 under 900 ℃ annealing. The mechanism of up-converted red light and green light are two-photon excited state absorption, and the blue light is three-photon excited state absorption.
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Chen, Hsiang-Yun. "Energy Transfer Dynamics and Dopant Luminescence in Mn-Doped CdS/ZnS Core/Shell Nanocrystals." Thesis, 2012. http://hdl.handle.net/1969.1/148167.
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Mn-doped II-VI semiconductor nanocrystals exhibit bright dopant photoluminescence that has potential usefulness for light emitting devices, temperature sensing, and biological imaging. The bright luminescence comes from the 4T1→6A1 transition of the Mn2+ d electrons after the exciton-dopant energy transfer, which reroutes the exciton relaxation through trapping processes. The driving force of the energy transfer is the strong exchange coupling between the exciton and Mn2+ due to the confinement of exciton in the nanocrystal. The exciton-Mn spatial overlap affecting the exchange coupling strength is an important parameter that varies the energy transfer rate and the quantum yield of Mn luminescence. In this dissertation, this correlation is studied in radial doping location-controlled Mn-doped CdS/ZnS nanocrystals. Energy transfer rate was found decreasing when increasing the doping radius in the nanocrystals at the same core size and shell thickness and when increasing the size of the nanocrystals at a fixed doping radius.
In addition to the exciton-Mn energy transfer discussed above, two consecutive exciton-Mn energy transfers can also occur if multiple excitons are generated before the relaxation of Mn (lifetime ~10^-4 - 10^-2 s). The consecutive exciton-Mn energy transfer can further excite the Mn2+ d electrons high in conduction band and results in the quenching of Mn luminescence. The highly excited electrons show higher photocatalytic efficiency than the electrons in undoped nanocrystals.
Finally, the effect of local lattice strain on the local vibrational frequency and local thermal expansion was observed via the temperature-dependent Mn luminescence spectral linewidth and peak position in Mn-doped CdS/ZnS nanocrystals. The local lattice strain on the Mn2+ ions is varied using the large core/shell lattice mismatch (~7%) that creates a gradient of lattice strain at various radial locations. When doping the Mn2+ closer to the core/shell interface, the stronger lattice strain softens the vibrational frequency coupled to the 4T1→6A1 transition of Mn2+ (Mn luminescence) by ~50%. In addition, the lattice strain also increases the anharmonicity, resulting in larger local thermal expansion observed from the nearly an order larger thermal shift of the Mn luminescence compared to the Mn-doped ZnS nanocrystals without the core/shell lattice mismatch.
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Yu-Ping, Li, and 李御賓. "A Study on Up-converted Luminescence Properties of Er3+-doped Gd2Ti2O7 Nanocrystals and Films." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/51643065022876576680.
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碩士<br>國立中正大學<br>光機電整合工程研究所<br>102<br>The purpose of this paper is to change the different doping concentration and the process temperature to synthesize of Er3+-doped Gd2Ti2O7 powders and films, and to explore its fluorescence properties and characteristics of thin films.
Er3+-doped Gd2Ti2O7 nanocrystals were fabricated by the sol-gel method.Under the 980 nm laser excitation of the Er3+ (10 mol%) – doped Gd2Ti2O7 powder with annealing more than 800 ℃ can produce the up-conversion (405, 520, 545, and 650 nm; 2H9/2→4I15/2, 4H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2, respectively) and Stokes luminescence (1534 nm; 4I13/2→4I15/2).And the XRD shows that while the annealing temperature exceeds 800 °C, amorphous pyrochlore phase Er3+-doped Gd2Ti2O7 transfers to well-crystallized nanocrystals. The average crystal size can be observed by SEM that it increases from 80 nm to 200nm while the annealing temperature increases from 800 to 1200 °C for an hour.
We discuss optical properties and roughness of the Er3+ (0, 10, 20, 100 mol%)-doped Gd2Ti2O7film in different concentration and processing temperature.And then we coat colloidal phosphor on the glasses by spin coating. It is found that the average roughness is at 0.1 nm to 0.214 nm, and we use the method (by R.Swanepoel) to obtain the relations of film refractive index, optical band gap and packing density between the process temperature and doping concentration.
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Foxy and 邱智偉. "A study on preparation and luminescence properties of Er3+, Tm3+,Yb3+-doped Y2Ti2O7 nanocrystals." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/hg2h7s.
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碩士<br>國立中正大學<br>光機電整合工程研究所<br>100<br>Abstrct
The (Er3+, Tm3+, Yb3+)-codoped Y2Ti2O7 nanocrystals were synthesized by the sol-gel method in this work. We were focused on the fluorescent properties of different annealing temperature and different highest common factor a concentrations.
Er3+ &Tm3+& Yb3+ -codoped Y2Ti2O7 nanocrystals with particle size of 32~124 nm were synthesized by the sol-gel method. The green band centered at 547 nm (4S3/2 → 4I15/2) and red band centered at 660 nm (4F9/2 → 4I15/2) visiable emission and blue band centered at 488 nm (1G4→3H6) emission were observed in codoped nanoparticles under the 980 nm laser diode excitation. The total photon intensity were increasing by lower factor a and highest annealing temperature. The sample of (Er3+ 0.5%, Tm3+0.5%, Yb3+ 1%) -codoped Y2Ti2O7 nanocrystals have the best of brightness under 1000 ℃ annealing by photoluminescence spectroscopy measurement. The mechanism of up-converted red light and green light are two-photon excited state absorption, and the blue light is three-photon excited state absorption.
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Tseng, Yu-Jui, and 曾于芮. "Luminescence Properties of Cs4PbBr6 Perovskite Nanocrystals for the Application in Light-Emitting Diode Backlight Display." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/5ukgcv.
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碩士<br>國立臺灣大學<br>化學研究所<br>107<br>In recent years, the zero-dimensional Cs4PbBr6 crystals are respected as the new generation of functional materials for their good thermal stability and optical performance. Not only do the zero-dimensional perovskite Cs4PbBr6 nanocrystals retain the optical properties of traditional perovskite nanocrystals with a narrow full width at half maximum (FWHM) of ∼20 nm, high absorbance and high quantum efficiency, but they also solve a long-lasting stability problem in perovskite nanocrystals. However, the mechanism of the green emission from the Cs4PbBr6 crystals is still under debate. In order to solve this controversy, we attempt to clarify the controversy by using fluorescence spectrometer and confirm that the green light source of Cs4PbBr6.
In this study, the Cs4PbBr6 nanocrystals were successfully synthesized by low-temperature microemulsion method. The temperature tolerance of the structure was determined by temperature-dependent fluorescence spectroscopy. It was found that the 96% emission intensity was maintained after the high-temperature heating at 150oC. About the optical properties, the fluorescence behaviour of Cs4PbBr6 and CsPbBr3 were similar at low temperature. However, the previous literature pointed out that the band gap of Cs4PbBr6 is about 3.9 eV, so it should not emit the green light. Furthermore, the synchrotron XRD didn’t show the existence of CsPbBr3 phase. We proposed that it generated CsPbBr3 clusters which cause the strong green light in Cs4PbBr6 crystals. At the same time, we found that Cs4PbBr6 has strong absorption at 310 nm, but it could not be stimulated. However, when the temperature was lower than 200 K, Cs4PbBr6 emitted the light in 375 nm and 518 nm. This phenomenon proved the energy transfer, and it also showed the thermal quenching effect at room temperature. In addition, we hypothesized that the Cs+ vacancies in the Cs4PbBr6 nanocrystals induced the formation of CsPbBr3 clusters and we proved it by adjusting the ratio of different Cs/Pb precursors. While the Cs/Pb ratio decreased to 2.5, the quantum efficiency kept increasing and the product maintained the pure Cs4PbBr6 phase. It can be confirmed that the CsPbBr3 clusters were the reason for high quantum efficiency. When the Cs/Pb ratio was less than 2.5, the quantum efficiency quickly decreased and the CsPbBr3 impurity phase appeared. It indicated that the green light was not caused by the CsPbBr3 impurity. The optical properties of Cs4PbBr6 nanocrystals under different pressures were also determined by pressure-dependent fluorescence spectroscopy.
Compared with the traditional CsPbBr3 nanocrystals, the Cs4PbBr6 nanocrystals possess better stability and tolerance in environmental factors. These advantages make Cs4PbBr6 have better performance in the backlighting used light emitting diode. About the mechanism of the green light from the Cs4PbBr6 crystals, we also successfully clarified the debate. Finally, the Cs4PbBr6 crystals were succeeded fabricating as traditional WLED and Mini-LED which achieved high color gamut of 129% and 126% and proved Cs4PbBr6 nanocrystals are the potential material for backlight application.
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Hsia, Yuan-Lung, and 夏淵龍. "Photoluminescence of I-VII Semiconductor Compounds, ensitized Luminescence from “Deep States” Recombination in CuBr/AgBr Nanocrystals." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/12472942856643999311.
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碩士<br>高雄醫學大學<br>醫藥暨應用化學研究所碩士在職專班<br>95<br>The photoluminescence (PL) properties of CuBr and CuBr/AgBr semiconductor nanocrystals (NCs) embedded in borosilicate glasses are measured under band-to-band excitation by a 355 nm Nd:YAG laser. We observed emission from CuBr (peaked at 520 nm) doped glass, which is associated with deep states in CuBr NCs. We also observed the sensitized blue to orange-red emission in CuBr/AgBr-glass systems (peaked at 520 and 570 nm), in which the luminescence intensity of CuBr decreases with increasing AgBr concentrations, while it is enhanced significantly around 570 nm. The results are discussed by the possible energy transfer between them, or by the multi-exitonic recombination process which ejects an excited carrier from CuBr to AgBr NCs.
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Tu, Vu Duc, and 武得途. "Hybrid nanostructured materials based on upconversion nanocrystals for biomedical applications: Enhanced upconversion luminescence and Simultaneous bioimaging and photothermal therapy." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/4tb55z.
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博士<br>國立中正大學<br>物理系研究所<br>106<br>Lanthanide (Ln3+) doped upconversion nanoparticles (UCNPs) possess unique upconversion luminescence (UCL) properties which can generate ultraviolet-visible (UV-VIS) luminescence under continuous-wave near-infrared (NIR) excitation via a stepwise multiphoton absorption process. Up to date, UCNPs have been studied for diverse research applications in display, security, photovoltaic and biomedicine. Compared with traditional downconversion fluorophores, such as organic dyes, quantum dots and gold nanomaterials, UCNPs exhibits numerous advantages to serve as a biomarker for biomedical applications, including photostability, no photobleaching, no blinking, no autoluminescence, low scattering, high signal-to-noise ratio, narrow emission spectra band, large anti-Stokes shifts, long luminescence lifetimes, biocompatibility, low toxicity, and deep penetration depth in biotissues. Various types of highly efficient UCNPs have been developed; with a typical one comprises sodium yttrium fluoride (NaYF4) host co-doped with ytterbium (Yb3+) sensitizer ions and activator ions, for example, erbium (Er3+), thulium (Tm3+) or holmium (Ho3+). However, up to now UCL quantum yields of Ln3+ ions doped UCNPs are rather low, especially in aqueous solution, which limits them to be widely used in bio-imaging and bio-sensing applications. One of the greatest trends and major challenges in the field of UCNPs research is the quest to enhance UCL efficiency. In this thesis, we have developed some strategies for enhancing UCL of UCNPs such as surface passivation (that is, core@shell structure), boardband sensitization (that is, neodymium doing), photonic crystal engineering (that is, 1D resonant waveguide grating (RWG)). Besides, we have synthesized a novel multifunctional nanocomposite combining gold nanorod (AuNR) and NaYF4:Yb3+,Er3+ UCNP for simultaneous bioimaging, temperature sensing and in vitro photothermal therapy of oral cancer cells.
Firstly, we have utilized the core@shell structure and broadband sensitization approaches with two major goals: (i) To suppress the surface defect-induced UCL quenching by growing a crystalline shell around core nanocrystal, leading to enhance UCL intensity of UCNPs, (ii) To tune excitation wavelength to 795 nm by doping of neodymium (Nd3+), avoiding the overheating effect associated with the use of 980 nm excitation. A variety of core@shell structured UCNPs has been synthesized through thermal decomposition technique, including: NaYF4:Yb3+,Er3+@NaYF4 core@shell UCNPs, and NaYF4:Yb3+,Tm3+@NaYF4:Yb3+,Nd3+@NaYF4 core@shell@shell UCNPs. We demonstrate that UCL intensity of core@shell and core@shell@shell nanoparticles is one order of magnitude higher than those of corresponding core counterparts, indicating the important role of the shell as a shield from UCL quenching. Besides, the introduction of Nd3+ as sensitizer for UCNPs has ability to generate UCL emission under 795 nm excitation, overlapping with the first biologically transparent window in the range of wavelengths from 650 to 950 nm. This permits deep penetration depth into biotissues as well as low overheating effects. It is noteworthy that all the UCL emission bands of Nd3+-sensitized UCNPs under the excitation at 795 nm are enhanced about 3 to 4 times compared to those under the excitation at 976 nm, due to to the larger absorption cross section of Nd3+ at 795 nm.
We have also employed a RWG (a kind of photonic crystal substrate) comprised of a low-refractive index (low-n) mesoporous silica (n=1.22) sinusoidal grating layer and a thin high-n TiO2 waveguide layer to enhance UCL of NaYF4:Yb3+,Tm3+ core and NaYF4:Yb3+,Tm3+@NaYF4:Yb3+,Nd3+@NaYF4 core@shell@shell UCNPs with more than 104 times in aqueous solution. The structure parameters of the low-n RWG are optimized through rigorous coupled-wave analysis (RCWA) simulation to build up strong local electric field near the interface between TiO2 and aqueous solution under dual-wavelength excitations (976 and 795 nm). When the low-n RWG is illuminated by NIR laser with an incident angle matching with the guided mode resonance (GMR) angle of the low-n RWG, UCL emission is dramatically enhanced thanks to the build-up of strong local field on the surface of the low-n RWG. Besides, the UCL emissions can be further enhanced 2-4 times when the UCL emission wavelengths coincide with their associated GMR wavelengths. Then, we have found that the streptavidin-conjugated UCNPs bioprobes can be used to detect biotin molecules on the surface of the low-n RWG. The results confirm that the low-n RWG is feasible for UCL biosensing and bioimaging applications.
Finally, we develop a hybrid nanostructured material based on the combination of UCNPs and AuNRs having the same absorption at 980 nm. For photoluminescence bioimaging probes, the UCL of Ln3+-doped UCNPs using NIR light excitation have many advantages to be served as bioimaging or therapy agents. Photothermal therapy (PTT) is widely used as a treatment protocol for cancer therapy. Among various PTT agents, AuNRs are especially attractive because their high efficient of absorbing NIR light and converting heat energy through surface plasmon resonance (SPR). Besides, UCNPs can play a role as an nanothermometer to determine local temperature generated from AuNRs. Herein, we design novel multifunctional hybrid nanocomposites based on the conjugation of AuNRs with NaYF4:Yb3+,Er3+ UCNPs to combine UCL, temperature-dependence and SPR properties for fulfilling both luminescence labeling, temperature sensing and photothermal functions under a single 976nm excitation source. The nanocomposites with the help of antibody conjugation can effectively label Her2 marker on the surface of OML-1 oral cancer cells with good specificity. Because of strong absorption at 976nm excitation wavelength, AuNR-UCNP nanocomposites result in high efficiency of PTT effect to kill cancer cells dramatically under 976 nm laser irradiation. Our AuNR-UCNP nanocomposites exhibit simultaneous diagnostic in vitro bioimaging, temperature sensing and PTT, which is feasible for multimodal imaging guided PTT applications.
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Chiu, Shih-Hsuan, and 邱詩暄. "Matrix Effects on structural properties and luminescence of Ge nanocrystals formed by condensation of SiGe via high-temperature oxidation." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/xcgetg.
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碩士<br>國立交通大學<br>電子研究所<br>107<br>In this thesis, we summarized the process-controlled capability to produce Ge quantum dots (QDs) embedded within SiO2 and Si3N4 matrix. The matrix-strain imposed on the Ge QDs could be successfully modulated by changing the embedded materials and removing these embedded materials or not. The significant Raman shifts reveal that Ge QDs are subjected to 1.4% tensile strain, -0.55% compressive strain and -2.67 compressive strain, respectively, from embedded SiO2 and Si3N4 matrices.
Low-temperature photoluminescence (PL) spectra show that changing the strain state of the Ge QDs from compressive, unstrained to tensile, there appears a systematic blue shift in the major PL peak energy from 0.77eV, through 0.81eV to 0.84eV. The power-dependent and temperature-dependent PL spectra of un-strained and tensile strained Ge QDs pointed out the direct bandgap transition and radiative recombination of excitons in the Ge QDs. The temperature-insensitive carrier lifetimes extracted from transient PL measurement provided additional strong evidence of direct bandgap transitions for un-strained and tensile-strained Ge QDs. Considering a lower peak energy and a stronger temperature-dependent lifetime for the compressive strained Ge QDs, the origin for the PL from compressive strained Ge QDs might be non-radiative recombination from indirect band gap transitions.
This thesis also proposed an approach to produce condensed SiGe layer by thermal oxidation. However, the oxidation and post-anneal conditions have not been optimized so that we are not able to produce high-quality, single-crystalline SiGe films accordingly. And thus, no visible light emission yet.
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CHEN, YI-CHIA, and 陳奕嘉. "Study of Enhanced Luminescence and Stability of Cesium Lead Halide Perovskite CsPbX3 Nanocrystals by Cu2+-Assisted Anion Exchange Reactions." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/w8qtff.
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碩士<br>東海大學<br>化學系<br>107<br>All inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have good application for optoelectronic devices such as solar cell and LEDs due to their excellent optical properties such as tunable emission wavelength, bright PL emission, and high photoluminescence quantum yield (PLQY). However, owing to its unstable crystal structure, it cannot maintain the great optical properties, and its synthesis process is too cumbersome. Here, we used a simple anion exchange reaction of CsPbCl3 perovskite NCs to obtain CsPbCl3 and CsPbBr3-xClx NCs, which treated by CuX2-OLA and CuX-OLA (X = Cl, Br), respectively. We observed that the optical properties such as PLQY and stability of CsPbCl3 and CsPbBr3-xClx treated by CuX2-OLA complex are better than those treated by CuX-OLA. Furthermore, we also used in-situ PL and in-situ XRD to investigate the mechanism of anion exchange. At the in-situ PL measurement of CsPbCl3 treated by CuCl2-OLA, we observed that the PL intensity decrease sharply when CuCl2-OLA was added, and then gradually rise again in a short time. And a similar phenomenon was also observed in the in-situ XRD measurement. Therefore, we infer that the mechanism of anion exchange involved structural destruction and recrystallization. This work is already published in The Journal of Physical Chemistry C.
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Dzurňák, Branislav. "Studium polovodičů metodami časově rozlišené laserové spektroskopie: Luminiscenční spektroskopie nanokrystalického diamantu." Doctoral thesis, 2012. http://www.nusl.cz/ntk/nusl-307932.
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Title: Study of semiconductors by methods of time resolved laser spectroscopy: Luminescence spectroscopy of nanocrystalline diamond Author: Branislav Dzurňák Department: Department of Chemical Physics and Optics Supervisor: doc. RNDr. František Trojánek, Ph.D. Abstract: The PhD thesis is focused on optical properties of nanocrystalline diamond prepared by chemical vapour deposition method. Photoluminescence of nanocrystalline diamond samples and effects of ambient temperature, pressure, pH and UV irradiation on it are studied by laser spectroscopy. Results suggest the keyrole of water and air adsorbates which affect the energy states in the sub-bandgap region of diamond. Photoluminescence decay of samples of different surface termination and structure and its dependency on ambient pressure and temperature is studied by methods of ultrafast (picosecond and nanosecond scale) laser spectroscopy. Results are analysed by power-law decay function which fits well the luminescence decay curves and also describes the dynamics of charge carriers in states localised within the bandgap. The model of interaction of nanocrystalline diamond with air adsorbates is proposed. Non-linear optical properties of nanocrystalline diamond are also studied, namely the generation of second and third harmonic frequency. The thesis...
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Lin, Ko-Chun, and 林可淳. "Interface traps of the N-type MOS structure with Ge nanocrystals characterized by G-V measurement and Si electron-luminescence." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/95863045534093738187.
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碩士<br>國立臺灣大學<br>電子工程學研究所<br>96<br>In this work, Metal-Oxide-Semiconductor structure with germanium nanocrystals formed by E-gun evaporator for charge storage and luminescence is fabricated. Fabricated devices are characterized by Transmission Electron Microscope. In the characterization of memory performance of devices with different PMA time, high frequency capacitance-voltage (C-V) measurement is used to measure the memory window for comparing the charge storage capacity. Frequency varied from 1000kHz to 5kHz which means exchanging speeds are slower, but the memory windows still exist. The carriers charged in Ge dots are independent of frequency. On the other hand, in conductance-voltage (G-V) measurement, the conductance of sample with PMA 1 minute is larger than sample with PMA 9 minutes, when frequency is more than 100 kHz. The result helps us to establish the model of the trap distribution, and characterize that PMA can neutralize the shallow trap. The peak values are larger with higher frequency and shift to positive bias, which means that the slow trap density is larger near band edge and smaller in mid band.
The luminescence mechanism is figured out by electron -luminescence (E-L) measurement. Holes are hopping though the traps in SiO2, and into Si substrate to recombination with the majority carriers-electrons. Triggered by DC mode, blackbody radiation caused by heat would effect Si E-L measurement. For improving luminescence efficiency, device must be triggered by the optimum frequency-1Hz matched the velocity of hole tunneling though oxide. Holes will be trapped in oxide instead of passing through in higher frequency, hence the recombination electron-hole pairs decreased. Luminescence of Si increased about 40 times, because of triggered by pulse mode.
Sample with PMA 13 minutes has better luminescence efficiency than sample with PMA 1 minute more than twice in time-domain luminescence measurement. This result agree with G-V measurement, which is PMA can neutralize the fast traps and make holes pass through oxide easier.
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Žídek, Karel. "Nelineární optické vlastnosti křemíkových nanostruktur." Doctoral thesis, 2010. http://www.nusl.cz/ntk/nusl-296108.
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Název práce: Nelineární optické vlastnosti křemíkových nanostruktur Autor: Karel Žídek Katedra (ústav): Katedra chemické fyziky a optiky Vedoucí disertační práce: Doc. RNDr. František Trojánek, Ph.D. E-mail vedoucího: trojanek@karlov.mff.cuni.cz Abstrakt: Disertační práce se zabývá nelineárními optickými jevy a ultrarychlým vývojem luminis- cence křemíkových nanokrystalů. Pomocí metody optického hradlování signálu (časové rozlišení až 250 fs) porovnáváme ultrarychlý vývoj luminiscence křemíkových nanokrystalů s různými ve- likostmi (v řádu jednotek nanometrů) a také s rozdílnými formami pasivace. Pro nanokrystaly, kde po excitaci dominuje vliv zachytávání nosičů do povrchových stavů nanokrystalu, navrhujeme teoretický popis závislosti rychlosti těchto procesů na vlastnostech nanokrystalů. Dále v práci podrobně zkoumáme působení Augerovy rekombinace, která se projevuje jak v časově rozlišené, tak i v časově integrované emisi vzorků. Experimentální data velmi dobře popisuje námi navržený model na bázi kinetických rovnic. Závěr práce se zaměřuje na zkoumání ultrarychle dohasínající stimulované emise. U stávajících metod měření optického zisku (VSL a SES) navrhujeme jejich rozšíření pro...
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Fučíková, Anna. "Bioaplikace nových nanostrukturních materiálů." Doctoral thesis, 2012. http://www.nusl.cz/ntk/nusl-312192.
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Title: Bioapplications of novel nanostructured materials Author: Anna Fučíková Department / Institute: Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. RNDr. Jan Valenta, Ph.D., Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University in Prague Abstract: This work is aimed at development of new fluorescent labels based on silicon nanocrystals. Nanodiamonds and commercial CdSe quantum dots have been used as comparative materials. Silicon nanocrystals are relatively small (1-4 nm) compared to other studied nanomaterials. They are prepared by electro-chemical etching and their surface can be activated by various molecules which strongly influences luminescence properties. Luminescence quantum efficiency can be as high as 30 % and perfectly photostable even in biological environment. Si nanocrystals are biodegradable in a living organism within reasonable time scale and non-toxic. We are able to detect luminescence of single nanocrystals, even inside living cells, with use of our micro-spectroscopy apparatus. Nanodiamonds have weak luminescence; they are toxic at higher dosages and very stable in living bodies (without available technique how to remove them). Studied CdSe...
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Kijatkin, Christian. "Ultrafast Photon Management: The Power of Harmonic Nanocrystals in Nonlinear Spectroscopy and Beyond." Doctoral thesis, 2019. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-201904011323.
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The present work broaches the physics of light-matter interaction, chiefly using nonlinear optical spectroscopy in a newly developed framework termed as Photon Management Concept. This way, existing fragments dealing with specific properties of harmonic and upconversion nanoparticles (HNPs/UCNPs) are consolidated into a full and coherent picture with the primary goal of understanding the underlying physical processes and their impact on the application side, especially in terms of imaging techniques, via suitable experimental and numerical studies.
Contemporary optical setups involving contrast-enhancing agents are frequently limited in their excitation and detection configurations owing to a specialization to a select number of markers. As a result, the bandwidth of experimental methods and specimens that may be investigated is severely restricted in a large number of state-of-the-art setups. Here, an alternative approach involving HNPs and UCNPs, respectively, is presented providing an overview from their synthesis to optical characterization and to potential fields of application. Based on their inherent flexibility based on their nonlinear optical response, especially in terms of wavelength and intensity tunability, the PMC alleviates prevalent limitations by dynamically adapting the setup to a sample instead of the preliminary culling to a reduced number of eligible specimens that must not change their optical properties significantly during investigation.
The use of HNPs supersedes such concerns due to their nearly instantaneously generated, strongly anti-Stokes shifted, coherent emission capable of producing radiation throughout the visible spectral range, including infrared and ultraviolet wavelengths. This way, HNPs transcend the traditional field of imaging and introduces potential applications in optomanipulation or holographic techniques. Thorough (nonlinear) optical characterization of UCNPs and alkali niobate HNP ensembles is performed to assess the fundamental physical mechanisms interwoven with numerical studies leading to their wide-ranging applicability. Final remarks show that HNPs are ideal candidates for realization of the PMC and yet hold an even further potential beyond current prospects.
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Biteen, Julie Suzanne. "Plasmon-Enhanced Silicon Nanocrystal Luminescence for Optoelectronic Applications." Thesis, 2006. https://thesis.library.caltech.edu/2333/1/Julie_Biteen_PhD_Thesis_2006.PDF.
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<p>On the path toward the realization of silicon-based optical emitters for integrated microelectronics, this thesis studies the optoelectronic properties of silicon nanocrystals as a function of their surface passivation and their interactions with plasmonic materials. The first part of the thesis utilizes controlled oxidation exposures and photoluminescence spectroscopy to verify previous theoretical and computational predictions of oxygen-related surface states that effectively narrow the energy band gap of small silicon nanocrystals. The focus of the second half of the thesis is on experimental and computational studies of enhanced luminescence from silicon nanocrystals in the near field of noble metal nanostructures.</p>
<p>Surface plasmon enhancement is a technique that has only recently been applied to semiconductor nanocrystal luminescence. This thesis thoroughly investigates the emission of silicon nanocrystals coupled to gold and silver nanostructures to achieve a new level of understanding of the enhancement effect. By pairing silicon nanocrystals to metal nanostructures, up to ten-fold increases in the luminescence intensity are realized, concomitant with enhancements of the radiative decay rate, the absorbance cross section, and the quantum efficiency. Moreover, coupling at the plasmon resonance frequency is used to tune the nanocrystal emission spectrum. A computational exploration of these experimental observations indicates that the enhancement effects can be ascribed to emission in the concentrated local field that results from the excitation of metal particle plasmon modes. Finally, the process of coupling silicon nanocrystal emitters to plasmonic metals is applied to a silicon-nanocrystal light-emitting diode, and enhanced electroluminescence is realized.</p>
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Fan, Huang-Yu, and 范晃毓. "The Luminescence effect of Multi-layer Ge nanocrystal in MOS." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/84184876876853288597.
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碩士<br>國立臺灣大學<br>電機工程學研究所<br>95<br>The advantage of the optoelectronic component of silicon germanium is fully compatible with the Si-based microelectronic chips. Because SiGe-based optoelectronic devices can be tailored from 1.3 to 1.55 um, it increases the importance of this material system to fiber communication applications. With the ripe process technology of the several key devices like SiGe-based light emitters, photodetectors, modulators, and waveguides, it also opens the door for Si-based optical and electronic integrated circuits (OEICs).
In this thesis we first fabricated a device which has the basic MOS structure and we embedded Ge nanocrystal in the oxide. This thesis point is that we fabricated different number of layer Ge nanocrystal and change post oxidation anneal time. Then we measure it. We try increasing the number of layer to increase the probability of Ge capture electron. Increase post oxidation anneal time to get whether Ge nanocrystal can form more like sphere independently.Finally, We measure our sample when we decreasing the temperature.Change these three factors and see the effect of EL
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Chiang, Yi-Ting, and 江宜庭. "Novel Synthesis of Perovskite Nanocrystals for Applications in Luminescent Solar Concentrator and Photocatalysis." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/p5arqh.
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碩士<br>國立交通大學<br>應用化學系分子科學碩博士班<br>107<br>In this thesis, we have devolped a robust hot-addition method (HAM) inspired by the hot injection method. HAM can solve the problem that the organic cation is easily decomposed at high temperature which cause difficulty for synthesizing the organic-inorganic hybrid perovskite nanocrystals. The HAM can synthesize highly crystalline and stable organic-inorganic perovskite nanocrystal with great photoluminescent quantum yield and tunable optical properties.
The MAPbBr3 and CsFAPbBr3 were successfully synthesized by the hot addition method, which proved that the HAM is applicable to various organic cations. The effects of different A cations and different synthetic processes on the optical properties of perovskite nanocrystals were investigated by following perovskite nanocrystals. CsPbBr3 was prepared by hot injection method. CsFAPbBr3 was generated by combining hot injection method and HAM. MAPbBr3 was synthesized by three different synthesis methods. The photocatalysis reactions chosen under solid-gas phase reaction conditions were carried out under blue LED light. Then, the differences in optical properties were used to explain the photocatalysis performance of different perovskite nanocrystals. Since MAPbBr3 photoluminescence lifetime is longer which let excited electrons can easily transmit for reduction reaction, MAPbBr3 has better performance than other component lead halide perovskites. Among the three types MAPbBr3, the MAPbBr3 synthesized by the participation of trace water in the reaction show superior catalytic activity and stability.
In addition, MAPbCl3 and Mn-doped MAPbCl3 (Mn: MAPbCl3) were prepared by HAM for the development of luminescent solar concentrator (LSC) applications. The Mn:MAPbCl3 perovskite nanocrystals show a remarkable Stokes shift up to 200 nm. Based on this property, solar concentrators had fabricated with MAPbCl3 and Mn:MAPbCl3 as the luminescent medium. The device still retain a certain transmittance while exhibiting high optical efficiencies of 1.2% and 3.3%, respectively. However, efficiency of LSC remained unaffected after enlargment of LSC device because high stoke shift (200nm) achieved by Mn doping supresses re-absorption of emitted photon.
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Stephanie, Lee. "Luminescent indium phosphide nanocrystals formed from single-source precursors using fluoride-containing ionic liquids." Thesis, 2018. http://hdl.handle.net/2097/39147.
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Master of Science<br>Department of Chemistry<br>Emily McLaurin<br>Quantum dot (QD) or semiconductor nanocrystal research has propagated extensively over the past few years due to increasing interest in long lasting, renewable, and safe applications such as solar cells and LEDs. Quantum dots are utilized for their size dependent optical properties that are based on the quantum confinement effect. Cadmium-based materials dominated early quantum dot research, which led to honing of syntheses and expansion of our understanding of various mechanisms. Recently, however, current applications, such as solar cells, LEDs, and displays, for everyday consumers require less toxic materials. Indium phosphide (InP) is a possible substitute for cadmium-based materials as it is not intrinsically toxic and emits in the visible region from 450-700 nm.
Despite the potential benefits to using indium phosphide, reproducible synthetic methods for obtaining stable QDs with narrow size distribution and high quantum yield still need to be refined. Using single-source precursors such as magic-sized clusters is a good starting place for addressing some of these challenges. InP magic-sized clusters are stable intermediates that are homogenously sized and readily isolable for later growth into InP nanocrystals. Our goal with the InP clusters was to determine their long-term stability and reproducibility as an InP precursor. The InP clusters are can be reproduced, have longer stability when stored as a solid, and we can produce luminescent nanocrystals.
Producing highly luminescent InP nanocrystals without the use of HF or shell growth is a challenge. We used the 1-methyl-3-butylimidazolium tetrafluoroborate as our ionic liquid to determine the effect of various ratios of ionic liquid to an InP separate-source precursor on quantum yield. The 1:10 ratio of precursor to ionic liquid provided the highest quantum yield of 21%. These reactions were difficult to reproduce, because there were many factors that affected
the synthesis, such as how soon the precursor is used, when the reactions are conducted in the microwave, and how the ionic liquid interacts with the microwave. When using 1-methyl-3-butylimidazolium hexafluorophosphate as our ionic liquid and the magic-sized cluster precursor, there was a spike in pressure in the microwave, and the reaction could not proceed due to the production of a gas. This ionic liquid is still capable of producing nanocrystals with an absorption feature.
Understanding the mechanism of how these ionic liquids improve luminescence can lead to safer and more efficient syntheses. Ligand stripping and exchange is also a valuable tool for uncovering information about the surface chemistry. The Lewis acid, BF3, formed adducts with native surface ligands and produces polar, stable nanocrystals. Refining the precursor synthesis so that it's reproducible and producing luminescent nanocrystals were both time consuming processes. This work serves an entry into understanding the process of surface passivation and surface composition of the luminescent InP nanocrystals produced with magic-sized clusters and ionic liquids.
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Lin, Jian-Hao, and 林建豪. "Study of luminescent mechanisms of silicon nanocrystals embedded in SiOX matrix、ZnO and In2Se3 semiconductors." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/85295411427980655551.
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