In the past decades, solid-state lighting based on phosphors as energy converters has been a fast-growing industry. Phosphorconverted white light-emitting diodes (pc-wLEDs) enable high-power applications and miniaturization; for this, the phosphor must have good stability and high efficiency. In order to satisfy this demand, phosphor plates have been proposed instead of conventional organic-based phosphor binders. In this review, such phosphor plates are categorized according to their synthesis methods, and the advantages and disadvantages of each category are detailed. In addition, we describe the major aspects of phosphor plates that require improvement for applications in high-power devices. For the fabrication of high-power LEDs, the phosphor configuration, color purity, porosity, and particle size of glass powders are key properties to enhance the luminescence efficiency and reduce the generation of heat inside wLED packages, thereby improving thermal stability. The advent of authentic, energy-efficient lighting in the home and workplace significantly affected the modern way of life. Beginning with the mass production of incandescent light bulbs, and with the subsequent evolution of fluorescence lights, lighting technology has developed rapidly in the last few decades. Since Edison's incandescent bulb in 1879, 1 artificial lighting has been developed to increase power output and decrease the size of the system. The development of red light-emitting diodes (LEDs) in 1962 2 and blue LEDs in 1993 3 allowed innovation in lighting and display. In particular, combinations of blue LEDs and yellow phosphors are used for many applications because they can realize cheap and efficient white solid-state lighting with several advantages including long lifetimes, eco-friendly behavior, and the capacity of miniaturization. 4-6In phosphor-converted white LEDs (pc-wLEDs), the phosphor converter dispersed in silicon resin (phosphor-in-silicon; PiS) is directly packed on a blue InGaN chip.7 When driven by a bias current, the emitted blue light absorbed by the phosphor is emitted as yellow light; together with the transmitted blue light, this constitutes white luminescence. However, this method lacks a red component, which entails the drawbacks of a poor color rendering index (CRI) and limited correlated color temperature (CCT). To overcome these drawbacks, one proposed method mixes yellow phosphors with phosphors having green to red emissions under blue excitation. 8 In pc-wLEDs, the color is primarily determined by the ratio of the blue emission from the LED chip to the yellow to red emission from the phosphor. However, the efficacy and brightness are determined by the converted yellow to red emission, as it contributes the bulk of lumens. In this configuration, the heat generated from the LED chip and phosphor cannot be efficiently dissipated because of the poor thermal stability and weak thermal conductivity of the resin, which causes luminous decay and color shifting in white light-emitting diodes (wLEDs).9 When the tempe...

Cesium copper halides (CCHs) show promise for optoelectronic applications, and their syntheses usually involve high-temperatures and hazard solvents. Herein, the synthesis of highly luminescent and phase-pure Cs 3 Cu 2 X 5 (X = Cl, Br, and I) and CsCu 2 I 3 via a solvent-free mechanochemical approach through manual grinding is demonstrated. This costeffective approach can produce CCHs on a scale of tens to hundreds of grams. Rietveld refinement analysis of the X-ray diffraction patterns of the as-synthesized CCHs reveals their structural details. Notably, the emission characteristics of green-emitting, chloride-based CCHs remain stable even at elevated temperaturesmaintaining 80% of initial PL efficiency at 150 °C. Lastly, a postsynthetic reversible transformation between zero-and one-dimensional CCH materials is demonstrated, indicating the labile nature of their crystal structure. The proposed study suggests that mechanochemistry can be an alternative and promising synthetic tool for fabricating high-quality lead-free metal halides.

Increasing the stability of lead halide perovskites (LHPs) is required for integrating them into light-emitting devices. To date, most studies toward this direction have primarily concentrated on improving the chemical stability of green-emitting LHPs. In this work, red-emitting CsPbI 3 −Cs 4 PbI 6 hybrid nanocrystals (NCs) were synthesized with a high photoluminescence (PL) quantum yield of ∼90%. Their hybrid structure was examined via structural (Rietveld) refinement analysis and transmission electron microscopy. Rietveld refinement also revealed that the black polymorph of CsPbI 3 NCs is an orthorhombic perovskite rather than a cubic one. The thermodynamic stability of the CsPbI 3 NCs in Cs 4 PbI 6 matrices is enhanced in both solutions and films for up to several weeks. The enhanced stability of the embedded CsPbI 3 NCs is attributed to the lowering of their Gibbs free energy, as determined on the basis of experimental data. Additionally, the hybrid NCs exhibit unprecedented emission stabilitymaintaining 65% of their original PL efficiency at 150 °C and improved aqueous stability.

Among the many potential Eu 2+ -activated sodium superionic conductor (NASICON)-based host materials, the Sc 3+based NASICON phosphor (Na 3 Sc 2 (PO 4 ) 3 :Eu 2+ ) is a promising phosphor material for high-power lighting applications owing to its unusual thermal stability at elevated temperatures. It has previously been shown that negative thermal quenching (TQ) can be tailored to zero TQ depending on the Eu 2+ concentration. However, the obtained zero-TQ composition has low photoluminescent quantum yields, which hinders its applicability to high-power lighting. Herein, we report a holistic study of the tuning of thermal stability from negative TQ to zero TQ while preserving the original emission efficiency by introducing Lu 3+ ions in Na 3 Sc 2 (PO 4 ) 3 :Eu 2+ . Furthermore, we fabricated a high-power white light-emitting diode using optimized Lu 3+ -doped Na 3 Sc 2 (PO 4 ) 3 :Eu 2+ as the blue component, delivering a high color-rendering index value of 90 with a high luminous efficiency value of 25 lm/W obtained at a flux current of 1000 mA. Therefore, the findings of this work provide novel scientific insights into the importance of structure−property relationships in designing highly efficient thermally stable phosphors for high-power lighting applications.

In the quest for new functional materials, Mn2+-activated metal halide perovskites (MHPs) were found to possess remarkable optical properties. However, they show low photoluminescence quantum yield (PLQY) and weak thermal stability. This is due to weak dopant–host interactions and strong phonon–lattice coupling at high temperatures of MHPs. Developing Mn2+-activated MHPs with a high PLQY and good thermal stability has become a highly versatile research area to meet current needs. Herein, we synthesized Mn2+ ion-activated Rb3(Cd1–x Mn x )2Cl7 layered metal halide perovskite (LMHP) and solved its crystal structure using direct methods. The Rb3(Cd1–x Mn x )2Cl7 LMHP exhibits an orange emission with a high PLQY of 88%, the highest among Mn2+-activated MHPs. Moreover, Rb3(Cd0.80Mn0.20)2Cl7 exhibits a zero-thermal-quenching (TQ) behavior, which is considered the first for the MHP family. Therefore, our results could pave the way for a search for new LMHPs with zero-TQ behavior for high-power optoelectronic applications.