High-quality epitaxial layers are directly related to internal quantum efficiency. The methods used to design such epitaxial layers are reviewed in this article. The ultraviolet C (UVC) light-emitting diode (LED) epitaxial layer structure exhibits electron leakage; therefore, many research groups have proposed the design of blocking layers and carrier transportation to generate high electron–hole recombination rates. This also aids in increasing the internal quantum efficiency. The cap layer, p-GaN, exhibits high absorption in deep UV radiation; thus, a small thickness is usually chosen. Flip chip design is more popular for such devices in the UV band, and the main factors for consideration are light extraction and heat transportation. However, the choice of encapsulation materials is important, because unsuitable encapsulation materials will be degraded by ultraviolet light irradiation. A suitable package design can account for light extraction and heat transportation. Finally, an atomic layer deposition Al₂O₃ film has been proposed as a mesa passivation layer. It can provide a low reverse current leakage. Moreover, it can help increase the quantum efficiency, enhance the moisture resistance, and improve reliability. UVC LED applications can be used in sterilization, water purification, air purification, and medical and military fields.

NaBaScSi₂O₇ doped with Eu²⁺ ions has been synthesized via a high-temperature solid-state reaction. The photoluminescence (PL) spectra of NaBaScSi₂O₇:Eu²⁺ phosphors demonstrate two emission bands centered at 421 and 500 nm due to the substitution of Ba²⁺ and Na⁺ ion sites with Eu²⁺ ions, respectively. Nd³⁺ and Pr³⁺ ions are introduced to re-construct the defect state of NaBaScSi₂O₇:Eu²⁺, which optimizes the long persistent luminescence (LPL) and photo-stimulated luminescence (PSL) properties of the as-obtained phosphor, respectively. The different release process of carriers trapped by defects contributes to a marked emission colour change of LPL and PSL from PL. The repeatability of write-in and read-out of carriers is confirmed by the LPL and PSL spectra after multiple cycles. The multi-functionalized dynamic fluorescence properties of the NaBaScSi₂O₇:Eu²⁺ phosphor as an optical storage material (OSM) provide a possibility for their application in concealed information encryption and dynamic anti-counterfeiting.

Lead–halide perovskite nanocrystals (PeNCs), especially those composed of iodine, suffer from degradation problems. Water vapor, oxygen, light, and heat can damage PeNCs and consequently quench their photoluminescence (PL). Thus, robust encapsulation against all these stresses is urgently required. In this study, inorganic encapsulation of mesoporous SiO₂, in conjunction with a high-temperature sintering synthesis process under an inert atmosphere, is introduced. This synthesis process is compatible with various halide contents, yielding PeNCs sealed in SiO₂ particles that emit PL emission covering the entire visible range from 420 to 700 nm. The PeNCs–SiO₂ sample showed remarkable stability after undergoing aging tests under various exaggerated stresses as well as mitigated thermal quenching during thermal cycling. The color gamut constituted by three PeNCs–SiO₂ samples approached 135.36% NTSC and 101.07% Rec. 2020, with remarkable chromatic stability. The PeNCs–SiO₂ can be blended into a photoresist and remains luminous during the development procedure, which is compatible with the photolithography process; this facilitates the mass production of color conversion layers. All these advantageous features show that the material proposed herein has great potential for application in full-color displays such as micro and mini light-emitting diode displays.