Alexandrite as a high-temperature pressure calibrant, and implications for the ruby-fluorescence scale

The wavelength shifts of the R1 and R2 fluorescence lines of alexandrite (BeAl2O4:Cr+3) have been experimentally calibrated against the ruby-fluorescence scale as a function of both hydrostatic and nonhydrostatic pressures between 0 and 50 GPa, and simultaneously as a function of temperatures between 290 and 550 K. The results can be expressed in nm as λ(R1)=680.26(±0.01)+8.7×10−3 (±0.3) (T−273)+0.292(±0.003)P +1.3(±0.1)×10−3 P2 and λ(R2)=678.63 (±0.01)+7.8×10−3(±0.2)(T−273)+0.031 (±0.003)P+0.8(±0.1)×10−3 P2, with pressure P in GPa and temperature T in K. Notably, we find that the pressure–temperature cross derivative of the fluorescence wavelength shifts are negligible for both ruby and alexandrite.