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AlGaN deep-ultraviolet light-emitting diodes grown on SiC substrates
摘要： The disinfection industry would greatly benefit from efficient, robust, high-power deep-ultraviolet light-emitting diodes (UV-C LEDs). However, the performance of UV-C AlGaN LEDs is limited by poor light-extraction efficiency (LEE) and the presence of a large density of threading dislocations. We demonstrate high power AlGaN LEDs grown on SiC with high LEE and low threading dislocation density. We employ a crack-free AlN buffer layer with low threading dislocation density and a technique to fabricate thin-film UV LEDs by removing the SiC substrate, with a highly selective SF6 etch. The LEDs (278 nm) have a turn-on voltage of 4.3 V and a CW power of 8 mW (82 mW/mm2) and external quantum efficiency (EQE) of 1.8% at 95 mA. KOH submicron roughening of AlN surface (nitrogen-polar) and improved p-contact reflectivity are found to be effective in improving the LEE of UV light. We estimate the improved LEE by semi-empirical calculations to be 33% (without encapsulation). This work establishes UV LEDs grown on SiC substrates as a viable architecture to large-area, high-brightness, and high power UV LEDs.
关键词： AlGaN LEDs,UV-C LEDs,light extraction efficiency,disinfection technology,AlN,external quantum efficiency,SiC,substrate removal
更新于2025-09-19 17:13:59
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Elucidating the structure and optimising the photoluminescence properties of Sr2Al3O6F: Eu3+ oxyfluorides for cool white-LEDs
摘要： Herein, Sr2Al3O6F in hexagonal symmetry was synthesized via a solid-state methodology. The X-ray diffraction pattern of Sr2Al3O6F was refined by the Rietveld refinement with lattice parameters a = 17.8232(1) ? and c = 7.2168(0) ?. The stability of the crystal structure is further confirmed from the results of bond valence sums and the global instability index. The theoretical calculations of the electronic and optical behaviors of the Sr2Al3O6F were analyzed by density functional theory and the obtained results of the lattice parameters and direct bandgap were found close to the experimental data. The chemical states and elemental composition of Sr2Al3O6F were also authenticated by X-ray photoelectron spectroscopy (XPS). To evaluate the suitability of the Sr2Al3O6F structure as high efficient red phosphor, a series of Eu3+ doped Sr2-xEuxAl3O6F (x = 0.0 to 0.10) were synthesized, which showed intense red-orange emission (5D0→7F1,2) at UV and blue excitations. The photoluminescence intensity corresponding to 5D0→7F2 transition decreased significantly for x = 0.10 due to the luminescence quenching. Nevertheless, further enhancement in photoluminescence of Sr1.9Al3O6F: Eu0.1 sample was realized with the substitution of 0.1 mol Ba2+ ion for 0.1 mol Sr2+ ion. The various radiative properties of the emission bands were also analyzed through the Judd-Ofelt theory. The optimized Sr1.8Al3O6F: Ba0.1/Eu0.1 phosphor showed high red color purity (> 95%), and moderate thermal stability of around 72% at 150 oC, suggesting that it could be an ideal red component for white-LEDs. A white-LED comprising the commercial yellow phosphor and the optimized sample showed bright white light having the CRI of 80.5%, CCT of 5510 K, and CIE of (0.33, 0.36) indicating that Sr1.8Al3O6F: Ba0.1/Eu0.1 phosphor is an appropriate red component for cool white-LEDs.
关键词： Eu3+-doping,Rietveld refinement,Hexagonal Sr2Al3O6F,density functional theory,white-LEDs,red phosphors
更新于2025-09-19 17:13:59
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Enhanced thermal stability of InP quantum dots coated with Al-doped ZnS shell
摘要： Colloidal InP quantum dots (QDs) have attracted a surge of interest as environmentally friendly light-emitters in downconversion liquid crystal displays and light-emitting diodes (LEDs). A ZnS shell on InP-based core QDs has helped achieve high photoluminescence (PL) quantum yield (QY) and stability. Yet, due to the difficulty in the growth of a thick ZnS shell without crystalline defects, InP-based core/shell QDs show inferior stability against QY drop compared to Cd chalcogenide precedents, e.g., CdSe/CdS core/thick-shell QDs. In this work, we demonstrate the synthesis of InP-based core/shell QDs coated with an Al-doped ZnS outer shell. QDs with an Al-doped shell exhibit remarkable improvement in thermal and air stability even when the shell thickness is below 2 nm, while the absorption and PL spectra, size, and crystal structure are nearly the same as the case of QDs with a pristine ZnS shell. X-ray photoelectron spectroscopy reveals that Al3+ in Al-doped QDs forms an Al-oxide layer at elevated temperature under ambient atmosphere. The as-formed Al-oxide layer blocks the access of external oxidative species penetrating into QDs and prevents QDs from oxidative degradation. We also trace the chemical pathway of the incorporation of Al3+ into ZnS lattice during the shell growth. Furthermore, we fabricate QD-LEDs using Al-doped and undoped QDs and compare the optoelectronic characteristics and stability.
关键词： quantum yield,QD-LEDs,photoluminescence,Al-doped ZnS shell,X-ray photoelectron spectroscopy,InP quantum dots,thermal stability
更新于2025-09-19 17:13:59
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Comparison of UV-LEDs and LPUV on inactivation and subsequent reactivation of waterborne fungal spores
摘要： Recently, the contamination of fungi in water supply systems has been an area of increasing concern, such as Aspergillus spp. and Penicillium spp. It can cause some waterborne issues such as odor, taste and formation of mycotoxins. Ultraviolet light emitting diodes (UV-LEDs) are considered as a potential alternative to conventional mercury lamps for water disinfection. This study has compared the performance of LPUV (low pressure ultraviolet) and UV-LEDs with emissions at 265, 280 nm and combination emissions at 265/280 nm to test inactivation efficiency, reactivation, viability and electrical energy consumption in the treatment of three water-borne fungal species (Aspergillus niger, Penicillium polonicum, Trichoderma harzianum) at a batch water disinfection system. The results showed that the performances of UV-LEDs were superior for the inactivation of fungal spores compared to the 254 nm (LP), while no statistically differences were observed among the UV-LEDs (p > 0.05). The average photoreactivation rate (k1) of fungal spores irradiated by UV-LEDs and 254 nm (LP) follows the order: T. harzianum > A. niger > P. polonicum. Compared with LPUV, UV-LEDs irradiation at 280 nm and 265/280 nm more efficiently inhibits photoreactivation, which was attributed to that irradiation of 280 nm and 265/280 nm would cause greater membrane damage and increase intracellular reactive oxygen species level of fungal spores according to the flow cytometric results. The electrical energy consumption of UV-LEDs was higher than that of LPUV, which was due to its lower wall plug efficiency. The results of this study can provide additional and beneficial information for the reasonable exploitation of UV-LEDs in water disinfection.
关键词： UV-LEDs disinfection,Membrane permeabilized spores,Reactivation,Intracellular reactive oxygen species,Fungal spores
更新于2025-09-19 17:13:59
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Degradation mechanisms of bias stress on nitride-based near-ultraviolet light-emitting diodes in salt water vapor ambient
摘要： Degradation mechanisms of nitride-based near-ultraviolet (near-UV) light-emitting diodes (LEDs) were systematically analyzed by applying forward- and reverse-bias stresses to them in a salt water vapor ambient. The surface temperature of the forward-bias stress sample was higher than that of the reverse-bias stress sample. The high temperature of the forward-bias stress sample accelerated the chemical reaction of the device structure with salt water vapors and led to faster degradation. Composition analyses of the sample surface and cross-section were conducted to investigate the failure mechanism. The analyses results indicated that the erosion of the indium–tin–oxide layer enhanced the diffusion of the conducting metal into the LED crystal. The proposed method can effectively characterize the quality of near-UV LEDs in a short duration.
关键词： failure mechanisms,bias stress,reliability,near-UV LEDs
更新于2025-09-19 17:13:59
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Cyan phosphors for full-visible-spectrum lighting: shining new light on high-CRI white pc-LEDs
摘要： Nowadays, solid-state lighting sources based on white light-emitting diodes (LEDs) are extensively replacing the traditional illumination devices (incandescent and fluorescent lamps) due to their unique and appealing properties, such as high efficiency, high brightness, long working lifetime, small size, fast response time and eco-friendliness. Because of this, white LEDs have permeated deeply into many important sectors, including indoor and outdoor lightings, signals, displays and therapeutic applications. In order to make sure that white LEDs can provide artificial lighting source with good color quality and high vision performance, there are several important figures of merit that are used to characterize white LEDs: color rendering index (CRI), correlated color temperature, luminous efficacy of radiation and luminous efficacy.
关键词： full-visible-spectrum lighting,Cyan phosphors,high-CRI white pc-LEDs
更新于2025-09-19 17:13:59
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Evaluation of growth and nutritional value of Brassica microgreens grown under red, blue and green LEDs combinations
摘要： Microgreens are rich functional crops with valuable nutritional elements that have health benefits when used as food supplements. Growth characterization, nutritional composition profile of 21 varieties representing 5 species of the Brassica genus as microgreens were assessed under light-emitting diodes (LEDs) conditions. Microgreens were grown under four different LEDs ratios (%); red:blue 80:20, and 20:80 (R80:B20, and R20:B80), or red:green:blue 70:10:20, and 20:10:70 (R70:G10:B20, and R20:G10:B70). Results indicated that supplemental lighting with green LEDs (R70:G10:B20) enhanced vegetative growth and morphology, while blue LEDs (R20:B80) increased the mineral and vitamin contents. Interestingly, by linking the nutritional content with the growth yield to define the optimal LEDs setup, we found that the best lighting to promote the microgreen growth was the green LEDs combination (R70:G10:B20). Remarkably, under the green LEDs combination (R70:G10:B20) conditions, the microgreens of Kohlrabi purple, Cabbage red, Broccoli, Kale Tucsan, Komatsuna red, Tatsoi, and Cabbage green, which can benefit human health in conditions with limited food, had the highest growth and nutritional content.
关键词： growth,Microgreens,LEDs,nutritional value,Brassica
更新于2025-09-19 17:13:59
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Ultrafast preparation of Europium(III) and Terbium(III) activated LaSr2F7 nanoparticles for white LEDs and anti-counterfeiting mark
摘要： Tunable color-emitting LaSr2F7 nanoparticle-based phosphor materials with single- or co-doped trivalent rare-earth ions (Eu3t/Tb3t) were synthesized via an ultrafast chemical precipitation technique. When Eu3t and Tb3t ions were doped into the LaSr2F7 nanoparticles, the photoluminescence behaviors were investigated and showed characteristic red and green emissions in their respective regions. Under 393 nm excitation, the LaSr2F7:xEu3t nanoparticles revealed the dominant red emission band (5D0 / 7F1) of Eu3t ions while the optimum doping concentration was obtained at 0.4 mol, indicating a quantum yield (QY) of 24.5%. Likewise, the LaSr2F7:yTb3t nanoparticles showed the f-f transition of Tb3t ions and an intense green-emission peak at 543 nm (5D4 / 7F5) was observed under 352 nm of excitation wavelength and the predominant doping concentration was 0.5 mol and the QY was estimated to be about 33.4%. By increasing the Eu3t ion concentration in the optimized LaSr2F7:Tb3t phosphors, the color emissions were turned from yellow to red under 365 nm excitation and the existed energy transfer ef?ciency in between the Tb3t and Eu3t ions was analyzed. Furthermore, the red-, green- and warm white-emitting devices were also fabricated by utilizing the optimal single- and co-doped samples for covering NUV chips. Ultimately, the LaSr2F7:Eu3t and LaSr2F7:Tb3t nanoparticles were further applied to a high-security ink for stabile anti-counterfeiting mark.
关键词： White LEDs,Ultrafast synthesis,Anti-counterfeiting mark,Energy transfer
更新于2025-09-19 17:13:59
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Performance analysis of GaN-based micro light-emitting diodes by laser lift-off process
摘要： In this study, a monochromatic GaN-based micro-light-emitting-diode (μLED) array was fabricated using flip-chip technology. The laser lift-off (LLO) process was employed to decrease the light divergence caused by the differing refractive indexes of sapphire (n = 1.77) and GaN (n = 2.4). The LLO-μLEDs considerably improve light collimation, compared with conventional flip-chip μLEDs containing a sapphire substrate. We highlight, in particular, the importance of the optical characteristics before and after LLO. Collimation of light was discovered to be 12% higher after removal of the sapphire substrate. The results are of high importance for understanding the optical properties of μLED arrays after LLO.
关键词： Light-emitting diodes,Micro-LEDs,Laser lift-off,GaN
更新于2025-09-19 17:13:59
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Analysis of dominant non-radiative recombination mechanisms in InGaN green LEDs grown on silicon substrates
摘要： Relationship between the external quantum efficiency (EQE) curves and the dominant non-radiative recombination mechanisms of InGaN green LEDs grown on silicon substrates were investigated. Through the analysis of the ABC+(cid:1)(cid:2)(cid:3)(cid:4) model, the significant drop in EQE at low current levels is due to an increasingly defect-related Shockley-Read-Hall (SRH) recombination. Under extremely low current densities, the defect traps can even become the dominant channel for the leakage current through the tunneling process, thereby reducing the efficiency of carrier injection into the active region. These observations were further supported by the carrier lifetime measurement. However, this fails to explain the droop in EQE at high current densities, especially when SRH recombination has been saturated. Our results show that carrier leakage has becomes dominant at high current density when Auger recombination has been less impossible. Reduced carrier leakage may lead to increased carrier injection efficiency, which in turn alleviates EQE droop.
关键词： silicon substrates,InGaN,non-radiative recombination,green LEDs,external quantum efficiency,carrier leakage
更新于2025-09-19 17:13:59