Dissertations / Theses on the topic 'Excitation uv'

Etude de la polymérisation radiochimique (rayon gamma) de l'acrylamide en présence de vinylcarbazole. Etude de la polymérisation photochimique (U. V. ) en présence de benzophénones solubles dans l'eau. Etude du mécanisme d'amorçage

Etude de l'echange de charge entre les ions o**(7+), ne**(7+), ar**(7+), kr**(7+), ar**(8+) kr**(8+) (8-80 kev) et hc ou h::(2), pour spectroscopie de photons. Analyse des spectres et identification de nouvelles raies pour la capture d'un electron par ar**(7+), ar**(8+), kr**(7+) et kr**(8+). Mesure des sections efficaces d'emission et deduction des sections efficaces des sous-niveaux nl et totales. Identification et mesure de la double capture radiative pour ar**(8+) et kr**(8+) avec hc, du processus de "transfert-ionisation pour ar**(8+) avec hc et h::(2), du processus de "transfert-excitation" pour ne**(7+) et ar**(7+) avec hc et h::(2). Pour n**(5+), proposition d'une methode nouvelle pour faire varier la fraction metastable du faisceau (1s2s **(3)s); mesure des sections efficaces de capture pour cet etat

The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany.

Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements.

When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m²) and the peak wavelength were maximum luminescence occurred.

The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected.

When irradiance of the excitation light was approx. 8 W/m² the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m². The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample.

The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.

Ce travail est consacré à l’élaboration de luminophores à base de polyphosphates d’ions alcalins et de terres rares, stœchiométriques ou activés en ions Eu3+ et Sm3+, émetteurs de fluorescence sous excitation VUV. Ces matériaux, de formulation LixNa1-xY1-yEuy(PO3)4 (x = 0 ; 0,25 ; 0,5 ; 0,75 ; 1 et 0,01 ≤ y ≤ 1), LixNa1-xLa(PO3)4 : 5 % Eu3+ (x = 0 ; 0,1 ; 0,2 ; 0,8 ; 0,9 ; 1), NaxK1-xLa(PO3)4 : 5 % Eu3+ (x = 0 ; 0,1 ; 0,2 ; 0,8 ; 0,9 ; 1) et LixNa1-xSm(PO3)4 (x = 0 ; 0,5 ; 1), ont été synthétisés par voie céramique et caractérisés principalement par diffraction des rayons X, spectroscopies infrarouge et Raman et analyses thermiques. Les analyses physico-chimiques et optiques, notamment grâce aux propriétés de sonde structurale de l’ion Eu3+, démontrent que la substitution croisée des ions alcalins Li+, Na+ et K+ n’est possible que dans une proportion relativement faible, ce qui lié aux différences de structures cristallographiques de ces matériaux. L’analyse des données spectroscopiques de l’ion Eu3+ selon la théorie de Judd et Ofelt confirme le lien étroit existant entre les propriétés optiques et structurales dans ces matériaux. Les spectres d’excitation sont caractérisés par une bande intense localisée dans le domaine VUV, respectivement due au mécanisme de transfert de charge Y3+-O2- et Eu3+-O2- dans les phases à l’yttrium dopées en ions Eu3+ et aux bandes 4f-5d pour les matériaux concentrés en ions Sm3+. Les matériaux concentrés en ions Eu3+ et Sm3+ sont émetteurs d’une intense fluorescence rouge et orange respectivement, démontrant l’absence d’extinction par concentration
This work is devoted to the development of phosphors based on polyphosphates of alkaline and rare earth ions, stoichiometric or activated with Eu3+ and Sm3+ ions, considered as light emitters under VUV excitation. These materials, with formula LixNa1-xY1-yEuy(PO3)4 (x = 0; 0.25; 0.5; 0.75; 1 and 0.01 ≤ y ≤ 1), LixNa1-xLa(PO3)4 : 5 % Eu3+ (x = 0; 0.1; 0.2; 0.8; 0.9; 1), NaxK1-xLa(PO3)4 : 5 % Eu3+ (x = 0; 0.1; 0.2; 0.8; 0.9; 1) and LixNa1-xSm(PO3)4 (x = 0; 0.5; 1), were synthesized in the solid state and characterized mainly by X-ray diffraction, infrared and Raman spectroscopies and thermal analysis. Physical-chemical and optical analyses, in particular using the Eu3+ ion as a structural probe, show that the cross-substitution of Li+, Na+ and K+ alkaline ions is possible only in a relatively small proportion, which is linked to the differences in crystallographic structures of these materials. The analysis of the Eu3+ ion spectroscopic data according to Judd and Ofelt theory confirms the close link between optical and structural properties in these materials. Excitation spectra are characterized by an intense band localized in the VUV domain, respectively due to the charge transfer mechanism Y3+-O2- and Eu3+-O2- for the Eu3+ doped yttrium materials and to the 4f-5d inter-configuration for the Sm3+ concentrated materials. Materials concentrated in Eu3+ and Sm3+ ions emit intense red and orange fluorescence respectively, demonstrating the absence of concentration quenching

A indústria optoeletrônica passa por um período de transformação em que os materiais inorgânicos estão sendo substituídos pelos orgânicos, oligômeros e polímeros, na fabricação de alguns tipos de dispositivos. No entanto, fatores como baixa eficiência e tempo de vida impedem que os aparelhos com base nos polímeros entrem definitivamente no mercado. Para resolver estas questões, é necessário um conhecimento profundo da estrutura eletrônica desses materiais. Apesar do avanço científico, ainda existem pontos a esclarecer. Por exemplo, não existe um consenso sobre a natureza das excitações óticas primárias e dos processos não radiativos nos polímeros conjugados, principalmente com excitação no ultravioleta. Tais processos limitam a eficiência e podem influenciar nos processos fotoquímicos, determinando o tempo de vida de um dispositivo. Esses fenômenos ocorrem em alguns picossegundos e, portanto, a espectroscopia ultrarrápida é a técnica mais adequada para o seu estudo. Neste trabalho, foi implementado o aparato para espectroscopia de bombeio e prova em filmes finos de polímeros conjugados, no qual podem ser usados dois métodos de aquisição de dados, sensível à fase e pulso-a-pulso. O primeiro é o método padrão citado na literatura, no qual o feixe de excitação é modulado por um chopper e os sinais são medidos por amplificadores lock-in. No segundo, o condicionamento de sinais é feito por circuitos amplificadores e o processamento dos sinais é feito pulso-a-pulso. É um método que a princípio fornece melhor estatística, pois as flutuações do laser são normalizadas pulso-a-pulso, e não na média. Além disso, apresenta menor custo e torna o experimento de bombeio e prova mais simples, pois os únicos procedimentos críticos passam a ser a sobreposição dos feixes na amostra e a determinação do atraso zero entre bombeio e prova. Foi projetado e construído o circuito eletrônico de condicionamento de sinais e o software de aquisição foi desenvolvido em linguagem LabVIEW. Entretanto, o método pulso-a-pulso forneceu uma sensibilidade inadequada para o estudo de filmes poliméricos, (ΔT⁄T ~ 0,7%, limitada pelo ruído elétrico na amplificação dos pulsos detectados), em contraste com ΔT/T ~ 0,1% que foi alcançada pelo método sensível à fase. Desta maneira, foi usado o último método para o estudo da evolução do espectro e da dinâmica de emissão estimulada de um filme de MEH-PPV, com excitação no visível e no ultravioleta, permitindo o estudo da dinâmica de relaxação dos estados de mais alta energia. Os resultados no visível são compatíveis com os da literatura, o que demonstra a confiabilidade do aparato quanto à sensibilidade e resolução temporal e espectral. Os resultados com excitação no UV indicam que a transferência de energia de bandas mais energéticas para a banda π - π∗ (conversão interna) ocorre em aproximadamente 300 fs, confirmando as suposições da literatura quanto à relaxação energética ultrarrápida (regra de Kasha), além de sugerir a existência de bandas ainda mais energéticas do que as já conhecidas. Pretende-se futuramente determinar a eficiência de tal transferência energética, pois ela pode ser um fator limitante na eficiência de fotoluminescência em polímeros conjugados com excitação no ultravioleta.
The optoelectronics industry is currently undergoing a transition period in which inorganic materials are being replaced by organic materials, oligomers and polymers, in the fabrication of some types of devices. However, factors such as low efficiency and low lifetime prevent polymer based devices on entering the market definitely. The solution of these issues requires a thorough knowledge of the electronic structure of these materials, but despite of scientific advances, there are still points to be clarified. For example, there is no consensus on the nature of the primary optical excitations and non-radiative processes in conjugated polymers, specially with ultraviolet excitation. Such processes limit the efficiency and can influence the photochemical processes, determining the device lifetime. These phenomena occur on a femtosecond timescale and therefore, ultrafast spectroscopy is the most appropriate technique for their study. In this work, we implemented the apparatus for pump-probe ultrafast spectroscopy on thin films of conjugated polymers, which can be used with two methods of data acquisition, phase-sensitive and shot-by-shot. The first is the standard method reported in the literature in which the excitation beam is modulated by a chopper and the signals measured by lock-in amplifiers. In the second, the detector signal conditioning is done by conventional amplifier circuits, followed shot-to-shot signal processing. This method provides the best statistics, in principle, because the laser fluctuations are normalized for each pulse, instead of using the average. In addition, the apparatus has a lower cost and the experiment is simpler, having as critical procedures the alignment of the beams on the sample and the determination of zero delay, with all other procedures done via software. The electronic circuitry for signal conditioning was designed and built and data acquisition software that enables measurements with both methods was developed in the LabVIEW programming language. However, the shot-by-shot method provided an inadequate sensitivity for the study of polymeric films (ΔT⁄T ~0.7%, limited by electronic noise in the amplification of detector signals), compared with ΔT⁄T ~ 0.1%, which was achieved by the phase sensitive method, and was the goal at the beginning of the project. Thus, the latter method was used to study the evolution of the spectrum and dynamics of stimulated emission of a film of MEH-PPV, with excitation in the visible and UV, allowing the study of the dynamics of higher lying electronic states. The results in the visible are consistent with those reported in the literature, which demonstrates the performance of the apparatus with respect to sensitivity and time/spectral resolution. The results with UV excitation indicate that the energy transfer among the more energetic bands to the π - π* band (internal conversion) occurs in about 300 fs, confirming the assumptions of the literature on the ultrafast energy relaxation processes (Kashas rule), besides suggesting the existence of even more energetic bands than those currently known. As future work, we plan to measure the efficiency of this energy transfer process, since it may be the limiting step in determining the overall photoluminescence efficiency of conjugated polymers with ultraviolet excitation.

L'oxydation et le vieillissement de la matiere se traduisent le plus souvent par des evolutions structurales entrainant des modifications de comportement. Ceci est particulierement important en industrie, notamment pour les produits fossiles et derives. Ainsi, les phenomenes de vieillissement des bitumes routiers peuvent etre suivis par differentes methodes physiques et rheologiques. Cependant, pour mieux les apprehender, il est necessaire d'etudier l'evolution chimique des bitumes, en preservant au maximum leur integralite (approche globale). L'etude de leur oxydation apres vieillissement par test rtfot (en film mince, a chaud et sous air) ou en service (sur la route), a ete menee ponctuellement par prise de spectres irtf et de fluorescence uv en excitation-emission synchrones (ees). L'evolution des bitumes a ete simulee par oxydation en continu, dans une cellule irtf mise au point a cet effet. Resituer les phenomenes naturels et les tests industriels, en comparant les indices obtenus en discontinu avec ceux en continu, a permis de mieux apprehender les chemins reactionnels de ces matieres organiques complexes. Dans cet objectif, des indices de vieillissement ont ete determines a partir des spectres des bitumes et de leurs fractions asphalteniques et malteniques. En fluorescence uv ees, ces indices traduisent l'etat de condensation des especes aromatiques presentes. En irtf, les indices decrivent les structures chimiques et les groupements fonctionnels. Leur evolution est correlee a celle des indices de fluorescence. Cette etude a permis de mettre en evidence des differences de reactivite selon l'origine du bitume (sa composition, etc. ) et les conditions d'utilisation. L'analyse en composantes principales (acp) des bitumes, en fonction soit de leurs proprietes rheologiques et mecaniques, soit de leurs indices spectrometriques, est semblable. En consequence, l'influence du taux et de la nature de certaines structures chimiques du liant sur ses proprietes rheologiques est indeniable. Il est maintenant possible, connaissant la structure initiale des bitumes, d'estimer sinon de prevoir une partie de leurs comportements rheologiques et chimiques, durant les vieillissements thermiques et sur site, par une regression multilineaire de certains indices spectrometriques. L'interet des outils analytiques developpes (indices spectrometriques d'irtf et de fluorescence uv), simples a realiser, ne s'arrete pas a l'etude du vieillissement des bitumes. En effet, l'etude prospective realisee sur les bitumes polymeres a aussi demontre la pertinence de l'information apportee par cette methodologie analytique. Les fractions bitumineuses responsables du gonflement du polymere ont ainsi ete determinees. De meme, il est possible, par comparaison avec une banque de donnees spectrales, de prevoir les phenomenes de demixtion de polymere au sein du bitume et l'interet industriel de ces melanges

Fluorescence techniques are being considered for the detection and identification of bacterial spores. This thesis sets out to empirically characterize the detailed autofluorescence spectroscopic properties of spores and their target molecules. The multiwavelength fluorescence studies from a unique endogenous biomarker, dipicolinic acid (DPA) and its calcium salt (CaDPA) in bacterial spores are found to be useful for fluorescence characterization of spores. A systematic determination of the fluorescence profile of the major chemical components of Bacillus spores and the effect of UV irradiation on them has been performed in dry samples, wet paste and in aqueous solution. The thesis applies reliable tools for accurately describing complex nature of spectral profile from bacterial spores, and for interpreting and identifying their spectral properties. We show that multiwavelength fluorescence technique combined with Principal Component Analysis (PCA) clearly indicates identifiable grouping among dry and wet Bacillus spore species. Differences are also observed between dried, wet and redried spores, indicating the stark effect of hydration on fluorescence fingerprints. The study revealed that changes in fluorescence of spores due to hydration/drying were reversible and supports a recent model of a dynamic and dormant spore structure. The spectra were analysed with PCA, revealing several spectroscopically characteristic features enabling spore species separation. The identified spectral features could be attributed to specific spore chemical components by comparing the spore sample signals with spectra obtained from the target molecules. PCA indicated underlying spectral patterns strongly related to species and the derived components were correlated with the chemical composition of the spore samples. More importantly, we examined and compared the fluorescence of normal spores with a mutant of the same strain whose spores lack DPA. We discovered that the dramatic fluorescence enhancement of Bacillus spores can be caused by UV irradiation in the spectral region of this unique biomarker without any pre treatment. Differences between spectra of spores, spore strains and other biological samples are very marked and are due to the dominance of the dipicolinate features in the spore spectra. This could lead to a cheap, more sensitive, faster and reagentless bacterial spore detector.

Fluorescence de nagdf::(4), k::(2)gdf::(5), gdcl::(3). Excitation selective dans l'ultraviolet (excitation a 1 photon) ou dans le rouge (excitation a 2 photons) d'une des composantes stark du multiplet **(6)p::(7/2) de gd**(3+). Le declin de la fluorescence entre 4,4k et la temperature ambiante permet de determiner le mode de diffusion de l'energie d'excitation. Effet de la densite d'excitation. Mise en evidence d'une fluorescence anti-stokes issue des niveaux **(6)g::(7/2), **(6)d::(3/2) et **(6)i::(7/2). Effet d'un champ magnetique

Les réponses optiques d'agrégats de métaux nobles sont caractérisées par une absorption intense, situées dans le domaine UV-Visible, et appelée plasmon de surface localisé. Pour des particules de plusieurs nanomètres de diamètre, le phénomène de plasmon peut être interprété par des modèles semi-classiques ou classiques comme la théorie de Mie, mais ces modèles trouvent leur limite lorsque la taille du système diminue. La théorie de la fonctionnelle de la densité dépendante du temps (TDDFT) est une approche entièrement quantique qui permet d'appréhender le phénomène de plasmon en reproduisant la réponse optique de petits agrégats d'argent, composés de quelques atomes à quelques centaines d'atomes. Dans ce contexte, nous avons réalisé des calculs TDDFT avec une fonctionnelle de type Range-Separated-Hybrid (RSH) sur des agrégats contenant entre 8 et 147 atomes d'argent. Les spectres obtenus sont en excellent accord avec les données expérimentales et les réponses optiques calculées perme ttent de retrouver les prédictions du modèle en couches. Nous présentons des outils permettant d'identifier et de caractériser les excitations plasmoniques dans le formalisme de la TDDFT. Les effets de l'environnement sur la réponse optique des agrégats sont également étudiés, avec notamment la présentation d'une méthodologie permettant de reproduire les spectres mesurés sur des agrégats d'argent piégés dans des matrices de gaz rare. Les effets de l'oxydation et les effets induits par une matrice de silice sur la réponse optique des agrégats sont également étudiés
Optical responses of noble metal clusters are characterized by a strong absorption in the UV-Visible range called localized surface plasmon. For clusters of several nanometers, the plasmon phenomenon can be interpreted by semi-classical or classical model, as the Mie theory, but those models can not describe the optical response of small-size clusters. The time dependent density functional theory (TDDFT) is a quantum method that allow to understand the plasmon phenomenon by reproducing the optical response of small silver cluster, made of a few tens or hundreds atoms. In this context, we performed TDDFT calculation using Range-Separated Hybrid (RSH) functionals over cluster containing between 8 and 147 silver atoms. The obtained spectra are in excellent agreement with the experimental ones and the calculated optical response allows to recover the shell model prediction. We present some tools that allow to identify and characterize plasmonic excitations within the TDDFT framework. The effect of the surrounding medium over the optical response of clusters are studied, in particular we will present a methodology that allow to reproduce spectra measured over clusters trapped in rare gas matrix. The effects of the oxidation and the effects induced by a silica matrix over the optical response of clusters are also studied

Etude spectroscopique des gaz purs et des melanges he-xe, excites par des particules alpha , entre 110 et 600 nm. Dans he observations de transitions moleculaires a 164 et 365 nm, et, en presence de co, du 1er systeme negatif (absence de v'=2). Dans xe, observation de deux continuums en uv proche et lointain et de la 2eme raie de resonance. Dans les melanges he-xe, observation en plus de la 1ere raie de resonance de xe avec renforcement des emissions de he par xe. Dans les melanges ne-co, emission du 1er systeme negatif et du 4eme systeme positif de l'ion et de la molecule; renforcement des emissions par addition de xe. Etude cinetique du 2nd continuum de xe dans les melanges he-xe a 173 nm (importance des processus heteronucleaires pour l'emission de l'excimere de xe) et du 4eme systeme positif dans les melanges ne-co (processus reactionnels a deux corps)

Principales proprietes thermoluminescentes des deux pics apparaissant a -170 et -40**(o)c : cinetique de remplissage des pieges impliques; caracteristiques spectrales (excitation et emission); blanchiments thermique et optique; parametres de piegeage, etc. . . Dosimetrie des rayonnements ionisants

Identification de 417 raies de ar i a ar ix et de nouvelles raies de ar vi a ar vii dans le domaine 90-850 a obtenues par impact d'ions lourds d'energie inferieur au mev/nucleon. Obtention de differents types de spectres suivant le fonctionnement du faisceau: 1) en continu, spectre total a 2 dimensions (intensite, longueur d'onde) correspondant a l'emission prompte, 2) en pulse, spectre a 3 dimensions (intensite, temps, longueur d'onde) associe a l'emission retardee. Mise en evidence de phenomenes de capture electronique par collisions secondaires entre ions de recul et ar neutre, conformement aux previsions du modele classique de la barriere de potentiel

碩士
崑山科技大學
機械工程研究所
101
The main purpose of this thesis is to develope a new phosphate fluorescent material and to study its characteristics. Potassium phosphate strontium (LiSrPO4) with orthorhombic structure doped with the metal ion Eu3+, Tb3+ or Sm3+ as an activator is studied in this thesis. Additionally, we investigate the effects of the doping concentration and sintering temperature on the microstructural and optical properties of potassium phosphate, strontium (LiSrPO4) by scanning electron microscop (SEM), X-ray diffraction (XRD), photoluminescence spectrum (PL), and Quantum Efficiency(QE). Results show that the optimum doping concentration of the activator Eu3+ is 7%, and the optimum sintering temperature is 1100 ℃. It is also found that concentration quenching occurred as a result of quadrupole-quadrupole (q-q) interaction according to the Dexter’s theory. When the doping concentration and sintering temperature are above the optimum values, the second phase appeared in LiSrPO4: Eu3+ structure has found. Moreover, the luminescence intensity can be influenced by concentration quench due to the excess doping concentration. When the Tb3+ activator is doped, the optimum doping concentration is 9%, and the optimum sintering temperature is 1100 ℃. The concentration quenching occurs as a result of dipole-dipole(d-d) interaction according to the Dexter’s theory. From the result of XRD, there is no second phase appeared in LiSrPO4: Tb3+ as the doping concentration of Tb3+ from 5% to 13%. However, as the sintering temperature increases to 1100 ℃, the degradation of the luminescence intensity occurs. Finally, when the Sm3+ activator is doped, the optimum doping concentration is 0.7%, and the optimum sintering temperature is 1100 ℃. It is found that the concentration quenching occurs as a result of dipole-dipole(d-d) interaction according to the Dexter’s theory. From the result of XRD, there is no second phase appeared in LiSrPO4: Sm3+ as the doping concentration of Sm3+ from 0.5% to 0.13%. However, as the sintering temperature increases to 1100 ℃, the degradation of the luminescence intensity occurs.

No
Violacein is a bisindole pigment occurring as a biosynthetic product of Chromobacterium violaceum and Janthinobacterium lividum. It has some structural similarities to the cyanobacterial UV-protective pigment scytonemin, which has been the subject of comprehensive spectroscopic and structural studies. A detailed experimental Raman spectroscopic study with visible and near-infrared excitation of violacein produced by C. violaceum has been undertaken and supported using theoretical DFT calculations. Raman spectra with 514 and 785 nm excitation of cultivated cells as well as extracts and Gaussian (B3LYP/6-311++G(d,p)) calculations with proposed molecular vibrational assignments are reported here.