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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Designing and Characterizing Metalenses for the Increased Light Extraction of MWIR LEDs
摘要： High radiance IRLEDs have been achieved, but much of the light created still remains in the device resulting in poor wall-plug efficiencies. Preliminary results presented here show increased light extraction by the addition of a 2D lens to the device, known as a metalens.
关键词： Mid-infrared LEDs,LED arrays
更新于2025-09-16 10:30:52
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Lithium ion doping triggered splendid quantum efficiency and thermal stability in Li <sub/>2</sub> SrSiO <sub/>4</sub> : <i>x</i> Eu <sup>2+</sup> phosphors for optical thermometry and high luminous efficiency white-LED
摘要： Eu2+/Li+-Codoped Li2SrSiO4 orange-yellow phosphors were developed for the applications of white light-emitting diodes (white-LEDs) and optical thermometry. Under near-ultraviolet and blue light excitation, the resultant phosphors exhibited the emissions of Eu2+ ions with an optimal doping concentration of 5 mol% and the concentration quenching mechanism was prevailed to be the dipole–quadrupole interaction. Through the incorporation of Li+ ions into the host lattices, the thermal stability and internal quantum efficiency of the synthesized phosphors were boosted. When the excitation wavelengths were 419 and 449 nm, the internal quantum efficiencies of the Eu2+/Li+-codoped Li2SrSiO4 phosphors were increased to 73% and 69%, respectively. The temperature dependent emission spectra were employed to characterize the thermal stability of the studied samples. The white-LED lamps utilizing the Eu2+/Li+-codoped Li2SrSiO4 phosphors as the orange-yellow component exhibited enhanced photoelectric properties. Furthermore, based on the temperature dependent bandwidth of Eu2+ ions, the thermometric performance of the resultant compounds was studied in detail and the maximum sensitivity was 0.049 K?1. The phosphors with multi-excitation wavelengths were suitable for high luminous efficiency white-LEDs and optical thermometers.
关键词： Li2SrSiO4,Eu2+/Li+-codoped,thermal stability,quantum efficiency,phosphors,white-LEDs,optical thermometry
更新于2025-09-16 10:30:52
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Effects of 1,2-ethanedithiol concentration on performance improvement of quantum-dot LEDs
摘要： We report systematic e?ciency variations of green-emitting CdSe@ZnS quantum-dot (QD) LEDs (QLEDs) in response to in situ treatments with 1,2-ethanedithiol (EDT) solutions at various concentrations. The main e?ect of in situ EDT treatment on a QD layer spin-coated onto a ZnO layer was vacuum-level shift due to dipole moments on the surface of the QD layer and at the interface between QD and ZnO layers. Competing contributions of these dipole moments were responsible for changes in energy level con?gurations and, accordingly, electron and hole barriers that resulted in discrepancies in electron- and hole-current variations. QLED e?ciency was best when treated with an EDT solution of 4 mM, attributable to the largest increase in the hole- to electron current ratio. The maximum luminous yield of the 4 mM EDT-treated QLED was 5.43 cd A(cid:1)1, which is 10 times higher than that of an untreated device. Furthermore, the luminous yield of this treated device remained as high as 2.56 cd A(cid:1)1 at a luminance of 500 cd m(cid:1)2.
关键词： efficiency improvement,vacuum-level shift,dipole moments,quantum-dot LEDs,1,2-ethanedithiol
更新于2025-09-16 10:30:52
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Combination of Light Emitting Diodes (LEDs) for photostimulation of carotenoids and chlorophylls synthesis in Tetradesmus sp.
摘要： In this work, Tetradesmus sp. was investigated regarding biomass and pigment production. The cultivation of Tetradesmus sp. was carried out in a BG-11 medium in addition to a vertical tubular photobioreactor (PBR) irradiated with different spectral combinations and intensities, within a 24:00 h photoperiod. The LEDs emitting light with white; red; yellow; green and blue spectrum were used alone and/or combined, with intensities varying from 13 to 190 μmol m?2 s?1. ANOVA suggested significant effects of the light combination, intensity and interaction between the factors on biomass, carotenoid and chlorophyll responses. The blue light accelerated the growth of Tetradesmus sp. in all three experiments. The combinations white:green (95 μmol m?2 s?1), red:blue (50 μmol m?2 s?1) favored biomass growth; while white:green (190 μmol m?2 s?1) favored the synthesis of carotenoids and chlorophylls. Culture reproduction under the spectral regions favoring pigment synthesis indicated that Tetradesmus sp. was photostimulated to synthesize both pigments, especially with red:green (50,50%) at 50 μmol m?2 s?1, where the highest production of carotenoids (6.09 ± 0.29 mg (g biomass)?1) and chlorophyll a (10.08 ± 0.75 mg (g biomass)?1) was obtained.
关键词： Tetradesmus sp.,Biopigments,LEDs
更新于2025-09-16 10:30:52
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Trichromophore-doped cassava-based biopolymer as low-cost and eco-friendly luminous material for bio hybrid white-light-emitting diodes by dual-FRET process
摘要： White-light-emitting diodes (WLEDs) are promoted as environmentally friendly because they are energy saving-features and mercury-free aspects, but, rare-earth-free, metal-free, cost-competitive, and eco-friendly for brighter WLEDs are attractive but quite challenging in practice. This paper reports a new methodology using biopolymer luminous material in bio hybrid white-light-emitting diodes (Bio-HWLEDs) based on a trichromophore-doped cassava crystalline thick film that emits bright white light emission through a dual F?rster resonance energy transfer (FRET) process. The dual-FRET takes place from coumarin to sulforhodamine via the curcumin chromophore. The Bio-HWLED showed color co-ordinates (0.33, 0.32) that exactly matched with pure white light emission. The effect of temperature on luminescence and the activation energy for thermal quenching were determined using the temperature-dependent photoluminescence measurements. Moreover, Bio-HWLED showed a low luminous drop rate of 0.00069 s?1 to overcome the aggregation-induced quenching effect. These results pave the way towards the realization of commercially viable, large-scale and high-contrast bio hybrid light applications that are environmentally friendly.
关键词： Chromophore,Cassava,Bio-LEDs,Dual-FRET,Quenching effect
更新于2025-09-16 10:30:52
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[IEEE 2019 41st Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC) - Berlin, Germany (2019.7.23-2019.7.27)] 2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) - A wearable phototherapy device utilizing micro-LEDs
摘要： A conformable device for wearable phototherapy applications is presented. The device consists of a 1mm thick elastomeric membrane edge-lit by specially fabricated micro-sized LEDs. Nanoparticle based scattering films are utilized to extract light and a uniform emission of 15μW/cm2 is reported over an area of 2cm2.
关键词： micro-LEDs,elastomeric membrane,light extraction,wearable phototherapy,uniform emission
更新于2025-09-16 10:30:52
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Novel multi-wavelength excitable single-component phosphor system for application in white-LEDs
摘要： A novel color-tunable phosphor of BaZnO2:xEu3+ (x=0 to 20 mol%) has been sucessfully prepared via high-temperature calcination method using alkaline earth metal as the charge compensator. Uncommonly, BaZnO2:Eu3+ is a multi-wavelength excitable phosphor due to its wide absorption spectrum ranging 250-550 nm. It shows broad white (400-700 nm), orange (~580 nm) and red (~611 nm) photoluminescence (PL) under 370 nm, 395 nm and 467 nm excitations, respectively and were assigned to one or more 5D0→7FJ (J =1 to 4) transitions of Eu3+ ion. An efficient energy transfer between Zn2+ and Eu3+ has been observed upon systematically increasing the concentration of Eu3+ ion. Scanning Electron Microscopy images indicated elongated rod-like structures with an average diameter of ~20 nm. The chromaticity coordinates (x, y) were found to be positioned at white (0.33, 0.42), orange (0.51, 0.42) and red (0.65, 0.34) regions correspond to 370 nm, 395 nm and 467 nm excitations, respectively. The temperature-dependent luminescence spectrum of BaZnO2:Eu3+ under the excitation of 467 nm was also studied. It exhibited good thermal stability and a marginal drop in photoluminescence intensity by 4.29% at 150oC was observed. The mathematical calculation of the activation energy was approximately 0.20 eV. The results indicate the suitability of the phosphor for LEDs applications, which is otherwise difficult to obtain in single-component system.
关键词： white LEDs,Phosphor,color tunability,photoluminescence
更新于2025-09-16 10:30:52
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Photo-microfluidic chip reactors for propene complete oxidation with TiO2 photocalyst using UV-LED light
摘要： In this study, we present a photo-microreactor illuminated with a low power LED light as a highly efficient system to achieve the total oxidation of propene using a TiO2 photocatalyst. This abatement system (photo-microreactor) consists in an immobilized benchmark photocatalyst (TiO2, P25) inside a commercial glass microchannel chip (UV transparent microfluidic chips, internal volume of 9.5 μl) using a packed-bed configuration without any previous treatment. The P25 inside the microreactor shows a nearly homogenous filling of the particles resulting in a low pressure drop throughout the system. In terms of propene abatement (Catalytic activity), the P25 inside the commercial microreactor reaches total propene conversion (100%) under flow conditions at low concentrations (100 ppmv) due to shorter diffusion distances, large surface-to-volume ratios, efficient heat transfer, and the improved light penetration inside the microchannel. Moreover, the prepared microreactor uses a low consumption power (LED), low residence time and presents a relatively low pressure drop making this device (P25 inside a commercial microreactor) very interesting for the abatement of volatile organic compounds at low concentration for example at indoor ambient due to its small size (45 × 15 mm).
关键词： Microreactors,LEDs,VOCs,Photocatalysis,TiO2
更新于2025-09-16 10:30:52
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Luminescence varied by selective excitation in Eu3+,Tb3+-doped LiSrPO4 phosphors for W-LEDs applications
摘要： Tb3+ and Eu3+-doped LiSrPO4 (LSPO) were produced via a modified sol-gel route. Structural and optical characterization was performed by X-ray diffraction (XRD) and photoluminescence spectroscopy (PL), respectively. The results reveal that the presence of dopants has an effect on the LSPO structure. PL spectra of the LSPO:Tb, Eu (LSPOTE) phosphor consisted of major emission lines associated with 5D3,4-7FJ (J = 3, 4, 5 and 6) and 5D0-7FJ (J = 0, 1, 2, 3 and 4) transitions of Tb3+ and Eu3+ ions, respectively. A change in emission spectra was observed when the excitation wavelength was changed. Under middle-ultraviolet excitation (227 nm), the Tb3+ and Eu3+-doped LiSrPO4 phosphor exhibited white emission. The results suggest that the LiSr0.97PO4:Tb0.01,Eu0.02 phosphors prepared in the present work could be used in combination with AlGaN chips to fabricate white LEDs.
关键词： Terbium,Lithium strontium orthophosphate,Europium,White LEDs
更新于2025-09-16 10:30:52
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Current Spreading Length and Injection Efficiency in ZnO/GaN-Based Light-Emitting Diodes
摘要： We report on carrier injection features in light-emitting diodes (LEDs) based on nonintentionally doped-ZnO/p-GaN heterostructures. These LEDs consist of a ZnO layer grown by chemical-bath deposition (CBD) onto a p-GaN template without using any seed layer. The ZnO layer (～1-μm thickness) consists of a dense collection of partially coalesced ZnO nanorods, organized in wurtzite phase with marked vertical orientation, whose density depends on the concentration of the solution during the CBD process. Due to the limited conductivity of the p-GaN layer, the recombination in the n-region is strongly dependent on the spreading length of the holes, Lh, coming from the p-contact. Moreover, the evaluation of Lh is not easy and generally requires the design and the fabrication of several LED test patterns. We propose a simple and effective method to calculate Lh, just based on simple considerations on I–V characteristics, and a way to improve the injection efficiency in the n region based on a noncircular electrode geometry. In particular, an interdigitated electrode structure is proved to be more efficient in terms of hole injection from n- to p-region.
关键词： zinc oxide (ZnO) nanorods,ZnO/GaN heterostructures,ZnO/GaN-based light-emitting diodes (LEDs),contact injection,current spreading length,Chemical-bath deposition (CBD)
更新于2025-09-16 10:30:52