Pressure dependence of the4T2and4T1absorption bands of ruby to 35 GPa

The pressure dependence of the ${}_{}{}^4{}_{}{}^{}$ ${\mathit{A}}_2$ ${\to }^4$ ${\mathit{T}}_2$ and ${}_{}{}^4{}_{}{}^{}$ ${\mathit{A}}_2$ ${\to }^4$ ${\mathit{T}}_1$ absorption bands of ruby have been studied to 35 GPa using a luminescence excitation technique developed for use at high pressure in the diamond anvil cell. The quasihydrostatic (Ar medium) pressure dependence of the zero-phonon lines, the crystal-field splitting parameter (Δ), and the Racah parameters B and C are determined. A significantly smaller variation of Δ is found for nonhydrostatic stress conditions for a ruby powder compact, and the implications of this on the pressure calibrations, lifetime measurements, and excitation of the R lines at high pressure are discussed.