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The emerging phase change materials (PCMs) have attracted much attention due to their unique properties and applications. However, the optical properties of PCM at high pressures have not been well explored. In this work, the microstructure and optical properties of GeTe and Sn-substituted GeTe at high pressures up to 30 GPa have been systematically investigated. We find that the substitution of small amounts of Sn for Ge combined with the introduction of high pressure can induce an optical contrast of 117% in crystalline GeTe, which is even higher than the highest optical contrast reported so far (90%) caused by amorphous GeTe to crystalline GeTe. The pressure-induced contrast does not originate from any phase transition as previously, but from the combined effect of Peierls distortion elimination and Ge vacancy formation, which leads to an increase in carrier concentration. The relationship between pressure/atomic composition, Peierls distortion/vacancy formation, and optical contrast can be well explained by a combination of experiments and theoretical calculations. Therefore, this study reveals the effect of high pressure on the optical properties of PCMs and provides new ideas for the design of high-optical-contrast PCMs. [ABSTRACT FROM AUTHOR]

The phosphor-in-glass (PiG) coating was fabricated via multilayer screen-printing and low-temperature sintering. The PiG coating consisted of Eu 2 O 3 -doped P 2 O 5 -ZnO-B 2 O 3 (PZB) glass, Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) yellow phosphor, and CaAlSiN 3 :Eu 2+ (CASN:Eu) red phosphor. Eu 2 O 3 and CASN:Eu were used to provide red emission for tunable chromaticity of white light-emitting diodes (LEDs), and surprisingly, the luminous efficacy was also enhanced. The impact of the variation in the B 2 O 3 content on the PZB glass and the effect of Eu 2 O 3 , YAG: Ce, and CASN:Eu on the luminescent properties of the PiG coating were investigated. The glass matrix with 8 mol% B 2 O 3 showed the lowest transition temperature and a suitable coefficient of thermal expansion. The spectra showed that the coating can be excited by blue light and produce yellow light and red light. The spatial distribution of the PiG coating was inspected by scanning electron microscopy, and it was observed that only a low erosion of phosphor by the glass matrix occurred. Furthermore, the white LEDs devices were constructed with the PiG coating on the blue LED chips. This method showed a decreased correlated colour temperature of 5137, a increased colour rendering index of 82.8 and an improvement in the luminous efficacy. The PiG coating for tunable chromaticity and enhanced luminous efficacy of white LEDs shows potential for application. [ABSTRACT FROM AUTHOR]