It is shown that at high pressures, results of absorption measurements are inconsistent with R-line fluorescence data. The observed constancy of $R_1$-$R_2$ splitting under hydrostatic conditions is supported by crystal-field analysis. The present findings suggest the need for absorption measurements in ruby crystals under more well-defined stress conditions.

• Received 27 February 1989

DOI:https://doi.org/10.1103/PhysRevB.40.3329