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Novel highly luminescent double-perovskite Ca2GdSbO6:Eu3+ red phosphors with high color purity for white LEDs: Synthesis, crystal structure, and photoluminescence properties
摘要： High-efficiency red-emitting phosphors are required to fabricate high-performance white light-emitting diodes (LEDs). Herein, the novel highly efficient Eu3+-activated Ca2GdSbO6 double-perovskite red phosphors with good thermal stability toward warm-white LEDs were reported. A series of Ca2Gd(1-x)EuxSbO6 red phosphors with different Eu3+ doping concentrations (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by using high-temperature solid-state reaction method. Under the excitation of 396 nm near-ultraviolet light, these Ca2Gd(1-x)EuxSbO6 phosphors showed intense red emissions peaking at 612 nm due to the 5D0→7F2 transition of Eu3+ ions. The strongest luminescence intensity reached when Eu3+ doping concentration was x = 0.5, and the critical distance between Eu3+ activators was calculated to be 7.97 ?. The concentration quenching mechanism was due to the dipole-dipole interaction of Eu3+ ions. The CIE color coordinates of the optimal Ca2Gd0.5Eu0.5SbO6 phosphors were determined to be (0.6629, 0.3367), and the corresponding color purity reached about 94.9%. Importantly, the Ca2Gd0.5Eu0.5SbO6 phosphors revealed outstanding internal quantum efficiency of 73% and good thermal stability. The emission intensity of Ca2Gd0.5Eu0.5SbO6 phosphors at 423 K still remained about 73% of its initial value at 303 K. Finally, a prototype white LED device was fabricated by coating the phosphor blend of commercial blue-emitting BaMgAl10O17:Eu2+ and our as-prepared red-emitting Ca2Gd0.5Eu0.5SbO6 on a 395 nm LED chip. Under 20 mA driven current, the device showed bright warm-white light with CIE color coordinates of (0.3888, 0.3943), correlated color temperature of 3911 K, and color rendering index of 88.4. The results demonstrated that the developed novel red-emitting Ca2Gd0.5Eu0.5SbO6 phosphors could be used as potential color converters in white LEDs.
关键词： White LEDs,Photoluminescence,Ca2GdSbO6,Double-perovskite,Eu3+ ions,Red-emitting phosphors
更新于2025-09-23 15:19:57
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Closed Loop Control of a Series Class-E Voltage-Clamped Resonant Converter for LED Supply with Dimming Capability
摘要： In this work, a new closed-loop control system is applied to a class-E resonant DC–DC converter with voltage clamp used for light-emitting diode (LED) supply. The proposed power topology was first described by Ribas et al. in a recent work. In the present paper, the LED current is sensed and used to implement a feedback control loop instead of the simplified feedforward scheme used in this previous reference. To design the control, a novel, simplified small-signal model is presented. This model is used to analyze the converter behavior as a function of the output power. The proposed approximation is significantly simpler than the multifrequency averaging technique normally used to analyze resonant converters. The feedback control loop is designed to reduce the LED low frequency current ripple while providing dimming control. Both the model and the control are verified by simulation and laboratory experimentation and the results obtained are in good accordance with the expected values.
关键词： small-signal dynamic model,light-emitting diode (LED) driver,high efficiency LEDs,resonant DC–DC converter,Class-E inverter,single-switch topology,closed-loop control,voltage clamp
更新于2025-09-23 15:19:57
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Thermophotonic cooling with light-emitting diodes
摘要： The currently ubiquitous light-emitting diodes (LEDs) have revolutionized the lighting industry. Contrary to common belief, however, LEDs are much more than just simple electricity-to-light converters. They are solid-state thermodynamic machines, theoretically capable of continuous and near-reversible energy conversion between electrical, thermal and optical energy. For over 50 years, the possibility of exploiting LEDs as efficient solid-state coolers has remained largely out of reach due to the high-material-quality requirements and commercial focus on light emission. Recent promising advances in electroluminescent cooling by LEDs, however, suggest that the remaining challenges in the area may be surmountable and practical cooling could be feasible. This Perspective discusses recent achievements in electroluminescent cooling, outlining the expected promise, the remaining challenges and their potential solutions.
关键词： solid-state thermodynamic machines,light-emitting diodes,electroluminescent cooling,LEDs,thermophotonic cooling
更新于2025-09-23 15:19:57
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Design of a Broadband NIR Phosphor for Security-Monitoring LEDs: Tunable Photoluminescence Properties and Enhanced Thermal Stability
摘要： Near-infrared (NIR) phosphors with capability for blue light to 850 nm broadband NIR emission conversion are highly desirable for security-monitoring LEDs. Targeted phosphor LaSc2.93-yGayB4O12(LSGB): 0.07Cr3+ (y = 0.6) is designed from the initial model of LaSc2.93B4O12(LSB): 0.07Cr3+ by chemical composition modification. The correlations among crystal-field environment, structural evolution, and luminescence properties of LSGB: 0.07Cr3+ (0 ≤ y ≤ 1.5) are elucidated by the Dq/B values, decay curves, and polyhedron distortion. The substitution of Sc3+ by Ga3+ in LSGB: Cr3+ (0 ≤ y ≤ 1.5) leads to decreasing structural polyhedron distortion and strengthened crystal field, consequently resulting in the blue-shift of broadband emission and enhanced thermal stability of LSGB: 0.07Cr3+ (y = 0.6) compared to that of LSB: 0.07Cr3+. The above results demonstrate that the superiority of blue-shift and enhanced thermal stability of LSGB: 0.07Cr3+ (y = 0.6) make it more suitable for the blue-pumped security-monitoring LEDs.
关键词： luminescence properties,crystal-field environment,security-monitoring LEDs,thermal stability,structural evolution,LaSc2.93-yGayB4O12(LSGB): 0.07Cr3+,Near-infrared (NIR) phosphors
更新于2025-09-23 15:19:57
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633-nm InGaN-based red LEDs grown on thick underlying GaN layers with reduced in-plane residual stress
摘要： This work investigates the in?uence of residual stress on the performance of InGaN-based red light-emitting diodes (LEDs) by changing the thickness of the underlying n-GaN layers. The residual in-plane stress in the LED structure depends on the thickness of the underlying layer. Decreased residual in-plane stress resulting from the increased thickness of the underlying n-GaN layers improves the crystalline quality of the InGaN active region by allowing for a higher growth temperature. The electroluminescence intensity of the InGaN-based red LEDs is increased by a factor of 1.3 when the thickness of the underlying n-GaN layer is increased from 2 to 8 lm. Using 8-lm-thick underlying n-GaN layers, 633-nm-wavelength red LEDs are realized with a light-output power of 0.64 mW and an external quantum ef?ciency of 1.6% at 20 mA. The improved external quantum ef?ciency of the LEDs can be attributed to the lower residual in-plane stress in the underlying GaN layers.
关键词： InGaN,n-GaN layers,residual stress,red LEDs,electroluminescence
更新于2025-09-23 15:19:57
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High performance GaN-based hybrid white micro-LEDs integrated with quantum-dots
摘要： Hybrid white micro-pillar structure light emitting diodes (LEDs) have been manufacture utilizing blue micro-LEDs arrays integrated with 580 nm CIS ((CuInS2-ZnS)/ZnS) core/shell quantum dots. The fabricated hybrid white micro-LEDs have good electrical properties, which are manifested in relatively low turn-on voltage and reverse leakage current. High-quality hybrid white light emission has been demonstrated by the hybrid white micro-LEDs after a systemic optimization, in which the corresponding color coordinates are calculated to be (0.3303, 0.3501) and the calculated color temperature is 5596 K. This result indicates an effective way to achieve high-performance white LEDs and shows great promise in a large range of applications in the future including micro-displays, bioinstrumentation and visible light communication.
关键词： hybrid white micro-LEDs,GaN,quantum dots
更新于2025-09-23 15:19:57
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Bicarbazole-based oxalates as photoinitiating systems for photopolymerization under UV-Vis LEDs
摘要： Photoinitiators are critical to initiate chain reactions in photopolymerization. For such applications, the absorption of photoinitiator must be compatible with the emission of light sources and enables the fast manufacturing of three-dimensional network or structures. Light-emitting diode (LED) is a new kind of energy-saving and environmental protection light source, exhibiting a substantial response in the near UV and visible range to replace the traditional mercury lamp and other light sources in photopolymerization. Here, we introduce methyl oxalate into bicarbazole chromophore (BiCz). By variation of the single or double substituents in the BiCz, we demonstrate that the absorption spectra can be adjusted and redshift to visible range and show good absorption in the near UV and visible range (365–475 nm). We explore their photochemistry based on experimental results and theoretical calculations and the mechanism of photoreactions have been verified. The super photostability by themselves and good hydrogen abstraction ability from amine co-initiator make them as excellent near UV and visible light active photoinitiators. Critically, the photoinitiation of the free-radical polymerization of acrylate monomers with low content (0.1% concentration) upon LED irradiation at 365–475 nm, exhibits excellent application potential in light curing and other fields.
关键词： free-radical polymerization,high efficiency,photoinitiators,UV–visible LEDs
更新于2025-09-23 15:19:57
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Synthesis and photoluminescence properties of a new blue-light-excitable red phosphor Ca2LaTaO6:Eu3+ for white LEDs
摘要： In this paper, a series of Eu3+-activated double-perovskite Ca2LaTaO6 (abbreviated as CLT:xEu3+; x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8) red-emitting phosphors have been successfully synthesized via the conventional high-temperature solid-state reaction method. These samples were characterized by X-ray diffraction, Rietveld refinement, field-emission scanning electron microscope, elemental mapping, energy-dispersive spectrum, room-temperature photoluminescence, decay lifetimes, quantum efficiency, CIE color coordinates, and temperature-dependent emission spectra. Interestingly, under blue excitation into the 7F0→5D2 transition of Eu3+ at 466 nm, the CLT:xEu3+ phosphors could emit bright red light corresponding to the 5D0→7FJ (J = 1, 2, 3, 4) transitions. Their luminescence properties have been investigated as a function of the Eu3+ ions concentration. It was found that the CLT:0.4Eu3+ sample exhibited the strongest emission intensity, and the concentration quenching effect was caused by the dipole-dipole interaction among Eu3+ activators. Impressively, the emission intensity of the as-prepared CLT:0.4Eu3+ phosphors was about 4.3 times higher than the commercial Y2O3:Eu3+ red phosphors. Moreover, the CLT:0.4Eu3+ sample had excellent CIE color coordinates of (0.665, 0.334) and supereminent color purity of 95.3%. Notably, the study on temperature-dependent emission spectra of the CLT:0.4Eu3+ sample revealed its good thermal stability and color stability at high temperatures. These excellent photoluminescence properties of CLT:0.4Eu3+ phosphors indicated their promising application potential in white light-emitting diodes as blue-light-excitable red phosphors.
关键词： Ca2LaTaO6,White LEDs,Red-emitting phosphors,Eu3+ ions,Double-perovskite,Photoluminescence
更新于2025-09-23 15:19:57
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Green and Orange Emissive Carbon Dots with High Quantum Yields Dispersed in Matrices for Phosphor-Based White LEDs
摘要： Carbon dots (CDs) have aroused more interest in the LED phosphor. High quantum yields and suppressing solid-state luminescence quenching are the key factors for CDs to prepare high-quality phosphors. In this work, orange and green emissive CDs (O-CDs and G-CDs) with very high absolute quantum yields (abs. QYs: 85.19% at natural pH and 96.12% at pH 9.0 for G-CDs; 34.89% in aqueous solution and 77.54% in ethanol for O-CDs) were achieved. Then, sodium silicate and PVA were selected as matrices to suppress their aggregation-induced quenching effect. Phosphor powder was prepared by microwave-assisted pyrolysis of sodium silicate and films by self-assembling of PVA in the presence of the CDs. The phosphor powder simultaneously containing G-CDs and O-CDs (G-O-CDs-phosphor) presents bright yellow fluorescence but owns a relatively low abs. QY. However, O-CDs/PVA and G-CDs/PVA phosphor films possess very high abs. QYs of 51.51% and 72.81%, respectively. LEDs constructed by coating G-O-CDs-phosphor on a blue chip exhibited a cool white color and a color rendering index (CRI) of 78. Interestingly, high-quality warm white LEDs owning a superior CRI of 93 were achieved by the O-CDs/PVA and G-CDs/PVA films. By comparison, PVA is more suitable to maintain the high performance of G-CDs and O-CDs for high-quality phosphors.
关键词： White LEDs,Phosphor,Carbon dots,High quantum yield,Rhodamine B
更新于2025-09-23 15:19:57
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Thin-film flip-chip UVB LEDs realized by electrochemical etching
摘要： We demonstrate a thin-?lm ?ip-chip (TFFC) light-emitting diode (LED) emitting in the ultraviolet B (UVB) at 311 nm, where substrate removal has been achieved by electrochemical etching of a sacri?cial Al0:37Ga0:63N layer. The electroluminescence spectrum of the TFFC LED corresponds well to the as-grown LED structure, showing no sign of degradation of structural and optical properties by electrochemical etching. This is achieved by a proper epitaxial design of the sacri?cial layer and the etch stop layers in relation to the LED structure and the electrochemical etch conditions. Enabling a TFFC UV LED is an important step toward improving the light extraction ef?ciency that limits the power conversion ef?ciency in AlGaN-based LEDs.
关键词： Thin-film flip-chip,AlGaN,light extraction efficiency,UVB LEDs,electrochemical etching
更新于2025-09-23 15:19:57