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To improve the luminescence properties of Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor, Sr.sub.2-xY.sub.xSi.sub.5-xAl.sub.xN.sub.8:Eu.sup.2+ specimens in which Sr.sup.2+ and Si.sup.4+ were partially substituted with Y.sup.3+ and Al.sup.3+ were prepared by carbothermal reduction nitridation. The obtained Sr.sub.2-xY.sub.xSi.sub.5-xAl.sub.xN.sub.8:Eu.sup.2+ samples showed standard Sr.sub.2Si.sub.5N.sub.8 structure. The effects of Y.sup.3+ and Al.sup.3+ partial substitution on the structures and luminescence properties of the resulting specimens were investigated. Under excitation by near UV and blue radiation, Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ exhibited a broad emission band at about 613 nm, originating from the 4f.sup.65d.sup.1 [right arrow] 4f.sup.7 transition of Eu.sup.2+. As Eu.sup.2+ concentration increased, the emission peak positions red-shifted from 606 to 628 nm, occupying two different crystallographic sites labeled as Eu(Sr1) and Eu(Sr2). Also, incorporation of both Y.sup.3+and Al.sup.3+ ions into Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ significantly increased the luminescence intensity of Eu.sup.2+. This was attributed to modification of the crystal field environment of Eu.sup.2+. Overall, the improved luminescence intensities obtained through partial substitution of Sr.sup.2+ and Si.sup.4+ by Y.sup.3+ and Al.sup.3+, respectively, indicated the promise of Sr.sub.2-xY.sub.xSi.sub.5-xAl.sub.xN.sub.8:Eu.sup.2+ as red phosphor candidates in white light-emitting diodes at x = 0.16.

One-dimensional CaMoO.sub.4:RE.sup.3+ (RE = Eu, Sm, Dy, Tb) nanofibers were successfully synthesized through a facile supersaturated recrystallization process. These CaMoO.sub.4:Ln.sup.3+ nanofibers have the length ranging from 40 to 70 nm and the width of nearly 2 nm. Under UV excitation, these single-doped CaMoO.sub.4 nanofibers shown stronger emission, and the photoluminescence quantum efficiency is 25.7% (CaMoO.sub.4:Eu.sup.3+), 22.4% (CaMoO.sub.4:Sm.sup.3+), 23.2% (CaMoO.sub.4:Dy.sup.3+) and 27.7% (CaMoO.sub.4:Tb.sup.3+), respectively. Moreover, our work reveals that various emission colors can be obtained and tuned from pure red to delight green via co-doping Tb.sup.3+ and Eu.sup.3+ in the CaMoO.sub.4 host, and the energy transfer properties from Tb.sup.3+ to Eu.sup.3+ are also demonstrated. Finally, we apply the green CaMoO.sub.4:Tb.sup.3+, red CaMoO.sub.4:Eu.sup.3+ and white CaMoO.sub.4:0.05Tb.sup.3+, 0.02Eu.sup.3+ for LED devices, and these nanofiber-based LEDs present high efficiency and stability, which indicates the promising application in future optoelectronic fields.

The Sm.sup.3+, Dy.sup.3+ doped and Sm.sup.3+/Dy.sup.3+ co-doped NaLa(MoO.sub.4).sub.2 spherical phosphors were hydrothermally synthesized by the EDTA-2Na mediated method. Under the excitation of 297 nm, the quenching concentration of Sm.sup.3+ in NaLa(MoO.sub.4).sub.2 host was determined to be 13%, and the concentration quenching mechanism was discussed to be the electric quadrupole-quadrupole interaction. After Sm.sup.3+ and Dy.sup.3+ ions were co-doped into the NaLa(MoO.sub.4).sub.2 host, the energy transfer behaviors resulted from Dy.sup.3+ to Sm.sup.3+ ions were investigated by the help of the luminescent spectra of the obtained phosphors. By varying co-doping concentrations of Sm.sup.3+/Dy.sup.3+ ions, the emission color of NaLa(MoO.sub.4).sub.2:Sm.sup.3+/Dy.sup.3+ can be tuned from reddish-orange, pink and white to bluish-green. The CIE chromaticity coordinate, the correlated color temperature and the quantum efficiency of NaLa.sub.0.87(MoO.sub.4).sub.2:1%Sm.sup.3+, 12%Dy.sup.3+ were calculated to be (0.356, 0.320), 4353 K and 20%, respectively. Furthermore, in the temperature-dependent analysis, it presented good thermal stability, which can become a promising single-phased white-emitting phosphor for white LEDs devices. Based on these results, the possible energy transfer mechanism between Dy.sup.3+ and Sm.sup.3+ in NaLa(MoO.sub.4).sub.2:Sm.sup.3+/Dy.sup.3+ was also proposed.

This paper presents an extensive literature review on Light-Emitting Diode (LED) fundamentals and discusses the historical development of LEDs, focusing on the material selection, design employed, and modifications used in increasing the light output. It traces the evolutionary trajectory of the efficiency enhancement of ultraviolet (UV), blue, green, and red LEDs. It rigorously examines the diverse applications of LEDs, spanning from solid-state lighting to cutting-edge display technology, and their emerging role in microbial deactivation. A detailed overview of current trends and prospects in lighting and display technology is presented. Using the literature, this review offers valuable insights into the application of UV LEDs for microbial and potential viral disinfection. It conducts an in-depth exploration of the various microorganism responses to UV radiation based on the existing literature. Furthermore, the review investigates UV LED-based systems for water purification and surface disinfection. A prospective design for a solar-powered UV LED disinfection system is also delineated. The primary objective of this review article is to organize and synthesize pivotal information from the literature, offering a concise and focused overview of LED applications. From our review, we can conclude that the efficiency of LEDs has continuously increased since its invention and researchers are searching for methods to increase efficiency further. The demand for LED lighting and display applications is continuously increasing. Our analysis reveals an exciting horizon in microbial disinfection, where the integration of UV LED systems with cutting-edge technologies such as sensors, solar power, Internet-of-Things (IoT) devices, and artificial intelligence algorithms promises high levels of precision and efficacy in disinfection practices. This contribution sets the stage for future research endeavors in the domain of viral disinfection using solar-powered UV LED modules for universal applications.

The advantages of light emitting diodes (LEDs) over previous light sources and their continuous spread in lighting applications is now indisputable. Still, proper modelling of their lifespan offers additional design possibilities, enhanced reliability, and additional energy-saving opportunities. Accurate and rapid multi-physics system level simulations could be performed in Spice compatible environments, revealing the optical, electrical and even the thermal operating parameters, provided, that the compact thermal model of the prevailing luminaire and the appropriate elapsed lifetime dependent multi-domain models of the applied LEDs are available. The work described in this article takes steps in this direction in by extending an existing multi-domain LED model in order to simulate the major effect of the elapsed operating time of LEDs used. Our approach is based on the LM-80-08 testing method, supplemented by additional specific thermal measurements. A detailed description of the TM-21-11 type extrapolation method is provided in this paper along with an extensive overview of the possible aging models that could be used for practice-oriented LED lifetime estimations.

At present, electric lighting accounts for ~15% of global power consumption and thus the adoption of efficient, low-cost lighting technologies is important. Halide perovskites have been shown to be good emitters of pure red, green and blue light, but an efficient source of broadband white electroluminescence suitable for lighting applications is desirable. Here, we report a white light-emitting diode (LED) strategy based on solution-processed heterophase halide perovskites that, unlike GaN white LEDs, feature only one broadband emissive layer and no phosphor. Our LEDs operate with a peak luminance of 12,200 cd m−2 at a bias of 6.6 V and a maximum external quantum efficiency of 6.5% at a current density of 8.3 mA cm−2. Systematic in situ and ex situ characterizations reveal that the mechanism of efficient electroluminescence is charge injection into the α phase of CsPbI3, α to δ charge transfer and α–δ balanced radiative recombination. Future advances in fabrication technology and mechanistic understanding should lead to further improvements in device efficiency and luminance.Heterophase CsPbI3 perovskite gives rise to bright white phosphor-free LEDs.

Organic light-emitting diodes (OLEDs) 1 – 5 , quantum-dot-based LEDs 6 – 10 , perovskite-based LEDs 11 – 13 and micro-LEDs 14 , 15 have been championed to fabricate lightweight and flexible units for next-generation displays and active lighting. Although there are already some high-end commercial products based on OLEDs, costs must decrease whilst maintaining high operational efficiencies for the technology to realise wider impact.  Here we demonstrate efficient action of radical-based OLEDs 16 , whose emission originates from a spin doublet, rather than a singlet or triplet exciton. While the emission process is still spin-allowed in these OLEDs, the efficiency limitations imposed by triplet excitons are circumvented for doublets. Using a luminescent radical emitter, we demonstrate an OLED with maximum external quantum efficiency of 27 per cent at a wavelength of 710 nanometres—the highest reported value for deep-red and infrared LEDs. For a standard closed-shell organic semiconductor, holes and electrons occupy the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs), respectively, and recombine to form singlet or triplet excitons. Radical emitters have a singly occupied molecular orbital (SOMO) in the ground state, giving an overall spin-1/2 doublet. If—as expected on energetic grounds—both electrons and holes occupy this SOMO level, recombination returns the system to the ground state, giving no light emission. However, in our very efficient OLEDs, we achieve selective hole injection into the HOMO and electron injection to the SOMO to form the fluorescent doublet excited state with near-unity internal quantum efficiency. Organic light-emitting devices containing radical emitters can achieve an efficiency of 27 per cent at deep-red and infrared wavelengths based on the excitation of spin doublets, rather than singlet or triplet states.