High-Pressure Synthesis of Corundum-Type Ga₂O₃:Cr³⁺ and Application of Its Fluorescence to the Pressure Scale

Cr³⁺-doped Ga₂O₃ crystals with a corundum structure were synthesized at high temperature and high pressure, and their excitation as well as fluorescence properties were evaluated. The crystals were green under white light illumination but deep red when exposed to ultraviolet light. This can mainly be attributed to R₁ and R₂ fluorescence spectra caused by the Cr³⁺ transition. The pressure-dependence of their fluorescence spectra is comparable with ruby (Al₂O₃:Cr³⁺), which is currently often used as a pressure scale. The excitation spectrum was shifted to the long-wavelength side compared with ruby, which enabled excitation with long-wavelength lasers, even if the pressure effect is considered. In addition, the R₁ and R₂ peaks were well-separated with increasing pressure, which might have advantages over the ruby scale.