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Double sites occupancy of Mn4+ in Cs2NaAlF6 with enhanced photoluminescence for white light-emitting diodes
摘要： In this work, we present a novel single-phase red phosphor of Cs2NaAlF6:Mn4t with two Al3t lattice sites, which shows two groups of vibrational phonon sidebands and ultra-intense zero phonon line (ZPL) under blue light illumination. The evidences have shown that the interesting spectral features originate from the non-equivalent occupation of Mn4t for both Al3t sites, which induces the neighboring cation vacancies surrounding Mn4t and highly distorted [MnF6] octahedral in the Cs2NaAlF6 host. The luminescent behavior of double sites occupied by Mn4t can absorb researchers’ interest on novel red-emitting phosphors. Pro?ting from the photoluminescence (PL) features, superior color rendering index of Ra ? 90.3, R9 ? 81, and low correlated color temperature of Tc ? 3967 K are achieved from white light-emitting diode (LED) by using yellow Y3Al5O12:Ce3t (YAG) and red Cs2NaAlF6:Mn4t phosphors as blue light converters. These results suggest that Cs2NaAlF6:Mn4t phosphor has a stupendous potential for LED lighting.
关键词： Red phosphor,Cs2NaAlF6:Mn4t,Luminescence properties,LED,Double sites occupancy
更新于2025-09-23 15:21:01
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Enhanced emission of Eu3+ in lutetium tungsten molybdenum oxide phosphors: Synthesis, optical properties, thermal behavior, and LED packaging
摘要： By adjusting molar ratios of raw materials of Lu2O3 (Eu2O3) to WO3 and MoO3 as well as WO3 to MoO3, several lutetium tungsten molybdenum oxide phosphors Lu2W0?5Mo0?5O6, Lu2WxMoyO9 (x t y ? 2), Lu2W1?5Mo1?5O12, and Lu6W0?5Mo0?5O12 were synthesized through a solid-state reaction method. The materials were characterized by X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) images, energy-dispersive spectra (EDS), diffuse reflection (DR) spectra, room temperature photoluminescence (PL) excitation and emission spectra, luminescence decay curves, and temperature dependent PL spectra. Red shift excitation bands were recorded in Lu2WxMoyO9 (x t y ? 2) phosphors with the concentration of Mo6t increasing. Enhanced Eu3t excitation and emission spectra were observed in the Lu2WxMoyO9 (x t y ? 2) phosphors with the concentration of W6t increasing. Possible energy transfer processes were proposed to explain the PL excitation and emission spectra. By combining phosphors with 365 nm ultraviolet (UV) chips, the obtained light emitting diodes (LEDs) gave bright red light under forward bias current. The results suggest that the obtained Eu3t doped Lu2WMoO9 have potential applications in phosphor converted based UV LEDs.
关键词： UV LED,Thermal properties,Phosphors,Optical properties,Photoluminescence
更新于2025-09-23 15:21:01
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Tunable bluea??greena??emitting Na4CaSi3O9:Ce3+,Li+,Tb3+ phosphor with energy transfer for near-UV white LEDs
摘要： Phosphor-converted white light emitting diodes (w-LEDs), with high luminous ef?ciency, low energy consumption, extended lifetime, and eco-friendly nature, have revolutionized various industries. Among them, an alkaline earth silicate-based phosphor host, Na4CaSi3O9, shows good crystal structure stability and ?exible properties for diverse application. Here, Ce3t/Lit and Tb3t/Lit co-doped Na4CaSi3O9 phosphors are fabricated by the standard solid-state reaction approach. The Ce3t/Lit-activated phosphors show strong absorption within 200e400 nm and exhibit a blue emission centered at 423 nm. The quenching concentration of Ce3t appears at x ? 0.05 and can be attributed to the dipoleequadrupole interaction. When Tb3t ions are co-doped, the Na4CaSi3O9:Ce3t/Lit phosphor emission can be adjusted from blue to green under the irradiation of 365 nm through the dipoleedipole interaction induced energy transfer from Ce3t to Tb3t ions with a maximum value of 28.32%. This study highlights the Na4CaSi3O9:Ce3t/Lit,Tb3t/Lit phosphors as a new and ef?cient material for w-LED applications.
关键词： Phosphor,Solid-state reaction,Luminescence,LED,Energy transfer
更新于2025-09-23 15:21:01
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Thermal and optical properties of high-density GaN micro-LED arrays on flexible substrates
摘要： Flexible GaN-based micron-size light-emitting diodes (μLEDs) with high brightness and low power-consumption are a promising technology for next-generation wearable displays. While, integrating GaN μLEDs onto flex can provide more functionality, the bending-induced strain and potential self-heating of the device are the challenges that degrade the device performance on plastic platforms. Here, a novel “paste-and-cut” approach to selectively transfer GaN μLEDs from sapphire substrates onto flexible platforms demonstrated the effectiveness of various intermediate metallic-bonding layers and LED geometries on the optical properties and performance of the flexible devices. Computational thermal simulation of the flexible μLEDs showed effective heat dissipation for devices mounted on plastic platforms bonded using a 0.5 μm thick Cu metallic pad to create stable optical emission (λ = 450 nm) under current densities of > 1 A/cm2. Through a finite-element analysis (FEA), it was determined that the applied stress-induced strain near the quantum wells of the μLEDs can be negligible for devices with diameters smaller than 20 microns. Experimental verification supported the simulation results; the diodes were found to be electrically and thermally stable when copper electrode layers > 600 nm thick was used to bond the LEDs onto the plastic platforms. The I-V characteristics of the μLEDs showed no measurable degradation after transfer onto the flexible substrate with a turn-on voltage of 2.5 V. Commensurate to the FEA simulations, no measurable optical wavelength shift was observed for LED having a diameter of 20 microns when driven at a current density of 1 A/cm2 under different mechanical strain.
关键词： Flexible Display,Heat Transfer,Invariant Emission,GaN Micro-LED
更新于2025-09-23 15:21:01
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AlInGaN-based superlattice p-region for improvement of performance of deep UV LEDs
摘要： A deep ultraviolet light-emitting diode (DUV LED) consisting of a specifically designed intermediate p-type region involving a superlattice quaternary nitride alloy has been proposed. The light output power of the proposed structure has been found significantly large; around 28.30 times high in comparison to the conventional structure, at the current density of 200 A/cm2. The maximum internal quantum efficiency of the proposed structure is 153.63% higher compared to the conventional one. Moreover, the efficiency droop has been reduced by 99.08%. Absence of abrupt potential barrier owing to the strain compensation provided by the superlattice p-AlInGaN layer offers an attractive solution for enhancing the hole injection into the active region leading to the improvement in performance of DUV LED.
关键词： Efficiency droop,Superlattice-AlInGaN,Strain compensation,DUV LED
更新于2025-09-23 15:21:01
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A High-Power-Factor Dimmable LED Driver with Integrated Boost Converter and Half-Bridge-Topology Converter
摘要： This paper proposes a dimmable light-emitting diode (LED) driver featuring a high power factor and zero-voltage switching on (ZVS). The circuit is obtained by integrating a boost converter and a dc-dc converter with half-bridge topology. The high power factor is achieved by operating the boost converter in discontinuous current mode (DCM). The LEDs are dimmed by the control scheme of asymmetrical pulse-width modulation (ASPWM). The developed circuit eliminates the inherited dc-o?set current of the transformer in a conventional asymmetrical half-bridge converter by introducing a balance capacitor. Both active switches can operate at ZVS by freewheeling the boost inductor current and the transformer magnetizing current to discharge the energy stored in their parasitic capacitance. The circuit operation is analyzed in detailed, and mathematical equations are derived. Finally, a 115-W prototype circuit for driving high brightness LEDs was built and tested. The experimental results verify the feasibility of the proposed LED driver with satisfactory performance. It can achieve a high power factor and ZVS operation.
关键词： power-factor correction,half-bridge converter,zero-voltage switching on (ZVS),asymmetrical pulse-width modulation (ASPWM),light-emitting diode (LED)
更新于2025-09-23 15:21:01
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Efficient N, Fe Co-Doped TiO2 Active under Cost-Effective Visible LED Light: From Powders to Films
摘要： An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO2 and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid, was evaluated on the degradation of (i) p-nitrophenol under UV-A light (365 nm) and (ii) rhodamine B under LED visible light (395 nm), and compared to undoped TiO2 film. The higher enhancement is obtained under the longer wavelength (395 nm). The possibility of producing photocatalytic films without any calcination step and active under low-energy LED light constitutes a step forward for an industrial development.
关键词： aqueous sol-gel process,Fe/N doping,LED visible light,titania,photocatalysis
更新于2025-09-23 15:21:01
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92.5% Average Power Efficiency Fully Integrated Floating Buck Quasi-Resonant LED Drivers Using GaN FETs
摘要： LEDs are highly energy ef?cient and have substantially longer lifetimes compared to other existing lighting technologies. In order to facilitate the new generation of LED devices, approaches to improve power ef?ciency with increased integration level for lighting device should be analysed. This paper proposes a fully on-chip integrated LED driver design implemented using heterogeneous integration of gallium nitride (GaN) devices atop BCD circuits. The performance of the proposed design is then compared with the conventional fully on-board integration of power devices with the LED driver integrated circuit (IC). The experimental results con?rm that the fully on-chip integrated LED driver achieves a consistently higher power ef?ciency value compared with the fully on-board design within the input voltage range of 4.5–5.5 V. The maximal percentage improvement in the ef?ciency of the on-chip solution compared with the on-board solution is 18%.
关键词： fully on-chip,gallium nitride (GaN),?oating buck converter,complementary-metal-oxide-semiconductor (CMOS),quasi resonance,integrated LED driver,heterogeneous integration
更新于2025-09-23 15:21:01
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Analysis of Approaches for Modeling the Low Frequency Emission of LED Lamps
摘要： Light emitting diode (LED) lamps are now an established lighting technology, which is becoming prevalent in all load sectors. However, LED lamps are non-linear electrical loads, and their impact on distribution system voltage quality must be evaluated. This paper provides a detailed analysis of time domain and frequency domain approaches for developing and evaluating models suitable for use in large scale steady-state harmonic power ?ow analysis of the low frequency (LF) emission of LED lamps. The considered approaches are illustrated using four general categories of LED lamps, which have been shown to cover the vast majority of LED lamps currently available on the market. The aim is an in-depth assessment of the ability of commonly applied models to represent the speci?c design characteristics of different categories of LED lamps. The accuracy of the models is quantitatively evaluated by means of laboratory tests, numerical simulations, and statistical analyses. This provides an example, for each LED lamp category, of comprehensive information about the overall accuracy that can be achieved in the general framework of large scale LF harmonic penetration studies, particularly in the assessment of voltage quality in low voltage networks and their future evolution.
关键词： power system harmonics,component-based model,frequency-domain model,time-domain analysis,LED lamps
更新于2025-09-23 15:21:01
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Three-Legs Interleaved Boost Power Factor Corrector for High-Power LED Lighting Application
摘要： In this article, a three-leg interleaved boost Power Factor Corrector (IBPFC) converter for energy-efficient LED lighting systems connected to the main grid was discussed. This IBPFC circuit presented features 60 kHz of commutation frequency and up to 3 kW of power rating. The controlled rectifier front-end boost PFC supplied a DC/DC converter to drive power LEDs suitable for street lighting or a lighting system for a stadium, etc. The IBPFC operated in continuous current mode (CCM). The ripple impact of the IBPFC converter was analyzed and a novel methodology of inductance design was presented. In the proposed design approach, the derivative calculation of the current ripple peak compared with the derivative of the input current was used to define a critical inductance value to ensure the CCM condition. Experimental validation was provided on a 3kW prototype.
关键词： IGBT,continuous current mode (CCM),interleaved converters,three-phase boost converter,ripple analysis,high-power LED lighting,power factor correction (PFC)
更新于2025-09-23 15:21:01