Letteratura scientifica selezionata sul tema "PC-LEDs"

Pc-LEDs, the lighting method that blends blue LED light with yellow light from phosphor to discharge white radiation, is one of the most advance known for high lumen output. However, pc-LEDs has inferior due to angular CCT deviation, which prevent pc-LEDs from reaching better performance. As a result, this research is conducted to address the need of pc-LEDs development by introducing a configuration doped with ZnO nanoparticles. The finite-difference time-domain (FDTD) method and the phosphor layer containing ZnO were applied in the experiments. The effect of ZnO-filled on the performance of color quality pc-LEDs is confirmed through calculated results. In particular, the uniformity of scattered light is improved with the presence of ZnO. In addition, ZnO particles also minimize the deviation of color temperature and enhance the color quality. Although there is a small decline in lumen output to achieve better color temperature uniformity, however, with suitable concentrations such as 0.25% N-ZnO, 0.25% S-ZnO, and 0. 75% R-ZnO, the decline is acceptable. The research on ZnO pc-LEDs demonstrates that this affordable and simple configuration can improve lighting properties and create other directions to enhance white light

We fabricated the photonic-crystal-structured p-GaN (PC-structured p-GaN) nanorods using the modified polystyrene nanosphere (PS NS) lithography method for InGaN/GaN green light-emitting diodes (LEDs) to enhance the light extraction efficiency (LEE). A modified PS NS lithography method including two-times spin-coating processes and the post-spin-coating heating treatment was used to obtain a self-assembly close-packed PS NS array of monolayer as a mask and then a partially dry etching process was applied to PS NS, SiO2, and p-GaN to form PC-structured p-GaN nanorods on the InGaN/GaN green LEDs. The light output intensity and LEE of InGaN/GaN green LEDs with the PC-structured p-GaN nanorods depend on the period, diameter, and height of PC-structured p-GaN nanorods. RSoft FullWAVE software based on the three-dimension finite-difference time-domain (FDTD) algorithm was used to calculate the LEE of InGaN/GaN green LEDs with PC-structured p-GaN nanorods of the varied period, diameter, and height. The optimal period, diameter, and height of PC-structured p-GaN nanorods are 150, 350, and 110 nm. The InGaN/GaN green LEDs with optimal PC-structured p-GaN nanorods exhibit an enhancement of 41% of emission intensity under the driving current of 20 mA as compared to conventional LED.

The <span lang="EN-GB">optimal spectral characteristics and photometric qualities in white-emitting light-emitting diodes (WLEDs) featuring red-emitting LEDs instead of phosphor (pc/R-WLEDs) were determined using the luminescent efficiency (LE) theory. The color quality scale (Rf) is higher than 97K for correlating color temperature (CCTs) ranging between 2700K and 6500K. We first identified genuine pc/R-WLEDs having Rf levels at 96–97, LE levels at 120–124 lm/W with CCT levels at 2969K, 4468K, 5682K, as well as 6558K with the utilization of all four-color phosphors: blues (448 nm), reddish (650 nm) LEDs, greenish (507 nm), and yellowish (586 nm). When compared to phosphorus-converted white-emitting LEDs (pc-WLEDs) and quantum dots white-emitting LEDs (QD-WLEDs), the pc/R-WLEDs, rather than the QD-WLED, would make better representatives of improved color version, notably in the reduced color temperatures, and could eventually replace current pc-WLEDs</span>.

The chromatic homogeneity and luminous efficiency are two crucial elements for determining a high-quality phosphor-converted LEDs (pc-LEDs). Thus, this paper provides essential information in choosing the particles to enhance lighting properties of high performance pc-LEDs. Scattering enhancement particles (SEP) such as CaCO3, CaF2, SiO2, and TiO2, are combined with yellow phosphor Y3Al5O12:Ce3+ and applied to the lighting devices. Initially, optical simulations are carried out with the support of LightTools program. Next, the Mie-theory is applied to calculate and confirm the results. The calculation subjects are SEPs scattering properties within the band 455 -595 nm. The scattering results of TiO2 suggest it is the optimal choice for pc-LEDs color quality in comparison to the other SEPs; however, it causes the luminous flux to decrease significantly along with the increase in its concentration. Besides, with the addition of SiO2 grains, we can accomplish higher lumen output at all particle sizes. Meanwhile, the application of 30% CaCO3 can decrease the CCT deviation by 620 K making CaCO3 the potential particle to be selected for chromatic quality and light output enhancement of pc-LEDs.

The high blue proportion of phosphor-conversion white-light emitting diodes (pc-LEDs), especially of those with higher correlated color temperatures (CCT), raises concern about photochemically induced retinal damages. Although almost all general lighting service LEDs are safe, other applications exist, like spotlights for theatres or at construction sites, that can pose a severe blue-light hazard (BLH) risk, and their photobiological safety must be assessed. Because of required but challenging radiance measurements, a calculative approach can be supportive for risk assessment. It is the aim of this work to exploit Gaussian functions to study LED parameter variations affecting BLH exposure. Gaussian curve approximations for color LEDs, the BLH action spectrum, and the spectral luminous efficiency for photopic vision enabled analytically solving the BLH efficiency, ηB, and the BLH efficacy of luminous radiation, KB,v. It was found that sigmoidal functions describe the CCT dependence of ηB and KB,v for different color LEDs with equal spectral bandwidth. Regarding pc-LEDs, variations of peak wavelengths, intensities, and bandwidths led to linear or parabolic shaped chromaticity coordinate correlations. ηB and KB,v showed pronounced CCT dependent extrema that might be exploited to reduce BLH. Finally, an experimental test of the presented Gaussian approach yielded its successful applicability for color and pc-LEDs but a minor accuracy for blue and green LEDs.

AbstractSol–gel formulations were applied to replace silicone as matrix material for phosphors in pc-LEDs. The content of organic groups was minimized in order to reduce yellowing during the operation of the elements. It was possible to evenly embed YAG:Ce particles in sol–gel binders. Further processing on LED chips resulted in operational light sources; and their performance was compared to standard silicone-based elements. Additional deposition of ALD laminates seals possible defects within the sol–gel matrix as additional protection of the phosphors and the underlying LEDs.

A Tungsten-Halogen (TH) lamp is the most popular light source in NIR spectroscopy and hyperspectral imaging, which requires a warm-up to reach very high temperatures of up to 250 °C and take a long time for radiation stabilization. Consequently, it has a large enough volume to enable heat dissipation to prevent the thermal runaway of the electric circuit and turn out its power efficiency very low. These are major barriers for miniaturizing spectral systems and hyperspectral imaging devices. However, TH lamps can be replaced by pc-NIR LEDs in order to avoid high temperature and large volume. We compared the spectral emission of the available commercial pc-NIR LEDs under the same condition. As a replacement for the TH lamp, the VIS + NIR LED module was developed to combine a warm-white LED and pc-NIR LEDs. In order to feature out the availability of the VIS + NIR LED module against the TH lamp, they were used as the light source for evaluating the Soluble Solid Content (SSC) of an apple through VIS-NIR spectroscopy. The results show a remarkable feasibility in the performance of the partial least square (PLS) model using the VIS + NIR LED module; during PLS calibration, the correlation coefficient (R) values are 0.664 and 0.701, and the Mean Square Error (MSE) values are 0.681 and 0.602 for the TH lamp and VIS + NIR LED module, respectively. In VIS-NIR spectroscopy, this study indicates that the TH lamp could be replaceable with a warm-white LED and pc-NIR LEDs.

Abstract In this study, the monolithic integration of LEDs with different emission colors (wavelengths of 543, 573, and 597 nm) with the directional radiation profiles was demonstrated. InGaN/GaN nanocolumn arrays ordered in a triangular lattice were prepared side by side, changing the diameter of the n-GaN nanocolumn (D n-GaN). The periodic arrangement of the nanocolumns led to the photonic crystal (PC) effect. The photonic band edge wavelength (λ B) and the InGaN bandgap were controlled by the D n-GaN. By controlling λ B closely at the bandgap wavelength, the PC effect provided directional beam radiation from the LEDs with radiation angles of approximately ±30°.

Ultraviolet (UV) light-emitting diodes (LEDs), as one of the more promising optoelectronic devices, are intrinsically limited by poor light extraction efficiencies (LEEs). To unlock the full potential of UV-LEDs, we propose a simple and effective strategy to promote the LEEs of UV-LEDs by screening and tailoring suitable optical structures/designs through rigorous numerical simulations. The photonic crystals (PCs) and/or nano-patterned sapphire substrates (NPSSs) equipped with the nano-pillar, nano-cone, nano-oval, and their derivates, are particularly investigated. The simulated results show that individual PC with an average transmittance of 28% is more efficient than that of individual NPSS (24.8%). By coupling PC and NPSS structures, a higher LEE with an average transmittance approaching 29% is obtained, much higher than that of the flat one (23.6%). The involved mechanisms are clarified and confirm that the promotion of optical performance of the nanostructured devices should be attributed to the widened response angles (from 0 to 60°), rather than the enhanced transmittances in the small angles within 30°.

Recent advances in solid state lighting (SSL) technology have encouraged its utilization in versatile applications. SSL technology based on phosphor converted light emitting diodes (pc-LEDs) are acting potentially as a substitute for traditional incandescent and fluorescent lamps on an account of their unprecedented luminous efficiency, low energy consumption, less emission of harmful gases, high brightness, compact design, fast switching and long working lifetimes. The pc-LEDs utilize phosphors coated on the LED chip capable of emitting light in desirable spectral regions upon an appropriate excitation. In the light of the above mentioned advantages, pc-LEDs are believed to be the next generation SSL technology and will bring a revolutionary changes in the lighting industry. For example, the white pc-LEDs have been the most preferred lighting devices for general illumination due to effective energy utilization, long lifetime, safety and so on. Moreover, pc-LEDs can be harnessed for indoor agricultural lighting owing to their excellence in controlling the spectral composition and lighting intensity to mimic the changes of sunlight during the day. Therefore, all the above mentioned fascinating features like effective energy saving and desirable light emission have enabled pc-LEDs to become economically feasible choice for general illumination and large scale indoor agricultural lighting applications around the corners of the world. The phosphor based w-LEDs can be developed by (i) coating of appropriate mixture of red, green and blue (RGB) phosphors excited with UV LED chip (ii) single yellow phosphor by a blue LED chip. However, reabsorption of blue color by RG phosphors in the former approach and lack of red component in later approach may lead to shortcomings like low color saturation, deteriorated color rendering index (CRI) and low color temperature stability. To overcome the above mentioned shortcomings, it is necessary to develop single phase phosphor doped with appropriate combination of rare earth ions (such as Dy3+/Eu3+, Tb3+/Eu3+ , Tb3+/Sm3+, Dy3+/Sm3+ etc.) providing white light emission via energy transfer or new red vii phosphor for the improvement of performance factors like luminous efficiency, CRI and correlated color temperature (CCT). Further, for plant growth under controlled environment fitted with smart pc-LEDs, it is necessary to conduct a widespread research for deep-red, far- red and blue light emitting phosphors that can be utilised to best drive photosynthetic metabolism and photo-morphogenesis as per the literature survey. Therefore, the ascending demand of energetically efficient lighting devices for general illumination and plant growth applications has led to a significant interest in the development of novel high quality phosphors with superior brightness, multiple emission color and excellent color purity. Besides lighting, the phosphors facilitate their utilization in diverse applications such as solar cells, bio-sensing and other optoelectronic devices due to their versatile physical, chemical and luminescent properties. In general, phosphor consisting of a host matrix (crystalline host) and an activator (luminescent center) have been pondered as a technologically significant components for the development of w-LEDs and agricultural lighting systems. In the past few decades, inorganic phosphors activated with rare earth (RE) ions have remained the prevalent protocol for fabricating pc-LEDs due to unique luminescence properties of RE ions. In such phosphors, the intermixing of oxygen atomic orbitals of host with orbitals of RE ion creates a specific crystal field environment around it such that transitions between incompletely filled 4f energy levels of RE ions deliver distinctive luminescence features. Also, the efficient energy transfer from the host crystal to the RE activators have been investigated to comprehend interesting optical phenomena. Among all the various inorganic oxides, vanadates have attracted acquiescent utilization in the wide-spread of luminescent device applications due to their wide-range of excitation wavelengths with abundant luminous colour, good physical and chemical stability. In addition, the vanadate materials are cost-effective and their preparation methods are energy efficient. The vanadate based phosphors give a broadband emission originating from inherent [VO4] 3- group. The broadband emission in the visible range by vanadate hosts can bring viii improvement in CRI and CCT values. Recent investigations have been established the possibility of achieving tunable visible emissions in RE activated vanadate phosphors via controlling [VO4] 3- to RE ions energy transfer. To harness the above mentioned precedencies, an investigation on a new ternary vanadate (CaBiVO5) phosphor doped with RE ions has been done for general and agricultural lighting applications. By incorporating suitable RE ions, the present host (CaBiVO5) can be tuned to emit different colors in the visible region suitable for pc-LEDs used in general illumination and agricultural lighting applications. Based on the extensive structural, morphological and photoluminescence characterizations, the outcome of the research work for accomplishing the research objectives has been organized in seven chapters. The brief summary of each chapter is as follows: Chapter 1 highlights the brief history, motivation, an outlook on the recent developments, potential challenges and great opportunities in white light generation and agricultural lighting. This chapter explains the basic concepts related to luminescence, spectroscopic features of RE ions, theoretical models implemented for examining the observed spectral data, and possible energy transfer processes. This chapter also present a brief viewpoint on the various characteristics and indices such as chromaticity coordinates, color purity, CCT and activation energy describing the color quality, thermal stability and performance of pc-LEDs. The importance of the present work and selected vanadate host have been discussed briefly in this chapter. At the last, the objectives of the thesis based on literature review have been included. Chapter 2 makes a thorough discussion about the different synthesis methods opted for the synthesis of single phase calcium bismuth vanadate (CaBiVO5: CBV) phosphors activated with different RE ions (Eu3+, Sm3+, Pr3+ and Dy3+). It also explicates the basic principle and working of experimental techniques employed to explore structural, morphological, optical and luminescent properties of CBV phosphors. The thermal and structural properties are studied by thermogravimetric analysis (TGA) and X-ray Diffraction (XRD) method, respectively. The ix scanning electron microscopy (SEM) reveals the morphology of the as synthesized phosphors. The optical properties are determined from diffuse-reflectance (DR) spectral measurements, while photoluminescence properties, thermal stability and decay kinetics of the CBV phosphors doped with different RE ions were investigated using spectrofluorophotometer. All these characterization techniques have been discussed in this chapter. Chapter 3 describes about the synthesis of single phase Eu3+ activated calcium bismuth vanadate (CaBiVO5) phosphors using solid state reaction method. X-ray diffraction (XRD) analysis confirms the pure phase formation and scanning electron microscope (SEM) micrographs exhibit inhomogeneous particle formation with irregular morphology of Eu3+ doped CaBiVO5 (CBV) phosphor. The photoluminescence excitation (PLE) spectrum indicates significant absorption in the ultraviolet (UV) and near ultraviolet (n-UV) spectral regions for un-doped CBV sample, whereas Eu 3+ doped CBV phosphors reveal various sharp absorption bands in n-UV and blue region along with host absorption bands. Trivalent europium activated CBV phosphors under 342 nm excitation exhibit dominant red emission peak at 613 nm wavelength accompanied by weak broadband originating from VO4 groups, whereas the phosphors under 464 nm excitation, exhibit similar emission profile with most intense one centered at 613 nm by excluding host emission bands. The energy transfer mechanism and the probable cause for concentration quenching beyond 4.0 mol% of Eu3+ ions concentration have been discussed in detail. The CIE chromaticity coordinates for the optimized phosphor, (0.551, 0.398) and (0.639, 0.358), situated in the reddish-orange and red region under 342 and 464 nm excitations, respectively. The CIE coordinates calculated based on the emission spectra measured under 464 nm excitation are close to the commercial phosphor Y2O2S: Eu3+ (0.622, 0.351). All the above mentioned results support the utilization of Eu3+ doped CBV phosphor as a potential red emitting component for luminescent devices. x The research work described in this chapter has been published in “Ceramics International 45 (2019) 15385-15393” (Impact factor =4.527) Chapter 4 describes the optimization of synthesis procedure for Sm3+ doped CaBiVO5 phosphor by preparing through it via three different synthesis methods, solid-state reaction (SR), combustion (CB) and citrate sol-gel (SG) method to enhance the luminescent properties. The pure phase formation of CBV: Sm3+ phosphors via diverse routes (SR, CB and SG) is confirmed as diffraction peaks for all prepared phosphors correspond to the standard data (JCPDS card no: 81-1775). The SEM results reveal that CBV: Sm3+ phosphors are synthesized with improved homogeneity and shape regularity at lower reaction temperature via SG method. The excitation spectra measured by monitoring the emission at 649 nm for CBV: Sm3+ phosphors reveal significant absorption in ultraviolet (UV), near (n)-UV and blue spectral regions. The comparative photoluminescence (PL) spectra measured under 343 nm excitation for differently synthesized CBV: Sm3+ phosphors, which exhibit significantly enhanced emission intensity for SG derived phosphor than other adopted methods. The PL spectra for SG derived 1.0 mol% Sm3+ doped CBV phosphor at λex = 275 and 343 nm exhibit sharp peaks located at 566, 606 and 649 nm along with weak host emission broadband and for λex = 406 nm, similar sharp peaks of Sm3+ transitions are observed without any host emission. Unlike mostly explored Sm3+ doped phosphors, emission peak in red spectral region (649 nm) is more intense as compared to the emission peak in orange region (599 nm) in the present work. The energy transfer mechanism responsible for concentration quenching in CBV phosphors is discussed in detail. The CBV: Sm3+ phosphors manifest color tunability from orange to orange- red region by modulating excitation from 275 nm (0.567, 0.404) to 343 nm (0.591, 0.399) and finally to 406 nm (0.620, 0.376). The temperature-dependent PL studies indicate appreciable thermal stability of as-prepared phosphor. Above mentioned results suggest that CBV: Sm3+ phosphor has great potential for use in white light-emitting diode (w-LED) applications. xi The research work described in this chapter has been published in “Optical Materials 107 (2020) 110119” (Impact factor =3.080). Chapter 5 describes the citrate sol-gel synthesis of Dy3+ activated and Dy3+/Eu3+ bi-activated calcium bismuth vanadate (CBV) phosphor to achieve white light emission and color- tunability. The phase purity and quasi-spherical particle with few agglomerations of the as- prepared CBV phosphors are indicated by structural and morphological characterizations, respectively. The emission spectral properties and energy transfer in Dy3+ doped and Dy3+/Eu3+ co-doped CBV phosphors have been examined extensively. The Dexter and Reisfeld’s approximation applied to emission spectra specifies electric dipolar-dipolar interaction to be accountable for Dy3+ to Eu3+ energy transfer. In CBV: Dy3+ phosphors, co-doping with Eu3+ ion facilitates red component that ensues warm white light emission as well as flexible color tunability with increasing Eu3+ ion concentration under different excitations. The significant findings like warm white light emission and controllable spectral composition in Dy3+/Eu3+ co- doped CBV phosphor by altering the excitation energy and co-dopant (Eu3+) concentration potentiate it as a suitable candidate in the domain of lighting and display devices. The research work described in this chapter is communicated to an Internationally reputed Journal “Solid State Sciences (2021)” (Impact factor = 3.059) Chapter 6 describes about orthorhombic Pr3+ -doped calcium bismuth vanadate (CBV: Pr3+) phosphors synthesized via citrate-gel method. The single-phase formation of CBV: Pr3+ phosphor has been endorsed by XRD analysis. The SEM image reveals dense-particle packaging with the quasi-spherical shape for the prepared CBV: Pr3+ phosphors. Under blue light excitation, CBV: Pr3+ phosphors exhibit intense red emission bands located at 608 and 656 nm wavelengths, overlapping with the absorption spectrum of PR phytochrome, which is present in plants. To achieve the maximum red intensity, the Pr3+ ion concentration is optimized xii to be 1.25 mol% in the CBV host, after which the emission intensity ceases due to the concentration quenching. Dexter's theory disclosed the possibility of d-d multipolar interaction among Pr3+ ions at higher concentrations of Pr3+ ions in the CBV host. The CIE coordinates are found to be positioned in the pure red region for CBV: Pr3+ phosphor and in the proximity of red-emitting commercial phosphor. The temperature dependent spectral studies manifest substantial thermal stability of the as-synthesized phosphor. All the studies mentioned above specify the tremendous potentiality of thermally stable CBV: Pr3+ phosphor in agricultural lighting and w-LED applications. The research work described in this chapter has been accepted to publish in “Journal of the American Ceramic Society 104 (2021) 5764-5775” (Impact factor =3.784). Chapter 7 summarizes the research outcomes of the work described in chapters 3 to 6 and outline the future scope of the thesis work for the expected applications.

Sensor devices such as pulse oximetry are practical tools used by most healthcare professionals, and even patients. An electronic sensor device that has the capability to measure physiological signs of saturation of arterial oxygen (SpO2) and heart beat rate of the human body has been developed in this study.The hardware design of the sensor device consists of a microcontroller PIC18F452, an external flash memory, and a transceiver unit. The most suitable sensors of red and infra red LEDs are installed on the arms of the plastic clip and functioned with the right resistor values. The red and infra red lights are detected by the photo diode and converted to digital numbers by the Assembly Language software program embedded into the microcontroller PIC18LF452. Those digital numbers are converted to SpO2 value in percentage level. A low power dual operational amplifier LM358 is used to amplify the current signal of the two lights, which depends on the intensity and visibility of the two lights. The output signals are displayed in 16 characters and 2 lines on Hitachi HD44870 compatible liquid crystal display (LCD). In order to display this data on personal computer (PC) monitor, the data is also transmitted via Universal Synchronous Asynchronous Receiver Transmitter (USART) ports of microcontroller to a PC. A Visual Basic 6 programming language is installed in the PC to display the wave forms, the percentage of the SpO2 level, and the pulse rate.Pulse oximetry has a promising future in the healthcare industry. This research enables a more efficient and economical means for managing the healthcare of the growing population.

Today, touch-screen-based handheld mobile devices are widely used; however, they are awkward to use with one hand. We propose MobiGaze, which is a user interface that uses one’s gaze to operate a handheld mobile device. By using MobiGaze, one can target the entire display area easily, even when the device is quite large. Moreover, MobiGaze can use both gaze and touch interactions. The combination of gaze and touch becomes a novel interaction paradigm. A gaze-and-touch interface effectively avoids the Midas-touch problem. The authors adopted a gaze-tracking method that uses a stereo camera to develop MobiGaze, because the user’s line of sight is detected in 3D. This allows the user to move the handheld mobile device freely. They constructed a prototype MobiGaze system, which consists of two cameras with IR-LEDs, a Windows-based notebook PC, and iPod touches. The authors evaluated the accuracy in a laboratory experiment and developed several applications for MobiGaze.

Este artigo detalha o procedimento de integração, incluindo projeto e simulação, de um conversor Buck-Boost atuando na correção do fator de potência (PFC) e de um conversor Forward como controlador de potência (PC). O circuito de conversores integrados é responsável por alimentar uma carga de LEDs que emitem luz de temperatura de cor distinta, possibilitando aplicações de iluminação circadiana. Resultados são mostrados a partir da análise das formas de onda utilizando o software PSIM, no qual foi observado boa correspondência entre os resultados teóricos e de simulação, validando o projeto proposto.

It has been widely accepted that solid state lighting, in terms of white light emitting diodes (LEDs), will be the fourth illumination sources due to their superior performance. In this study, an effective compact freeform lens design method for LED packaging was introduced. A compact silicone LED packaging lens with the refract index of 1.54 was designed for street lighting based on this method. Integrated with this small lens, a novel application-specific LED package, whose manufacturing process can be easily integrated into current LED packaging processes, was suggested. Two application-specific LED array modules, with the type of chip on board (CoB) package, were also designed by integrating 3×3 freeform silicone and polycarbonate (PC) lens arrays. Numerical simulation results demonstrated that the optical performances of these application-specific LED modules could directly meet the requirements of street lighting. By comparing with the traditional LED illumination module consisting of an LED and secondary optics, the novel application-specific LED packages have the advantages of low profile, small volume, high light output efficiency (LOE), low cost and convenience for customers to use, and they will probably become the trend of LED packages, providing more cost-effective solution to general lighting.