Pressure-Induced Shifts of R, R', and B Line-Groups and Ground-State Zero-Field-Splitting of Ruby

By means of improved ligand-field theory, the 'pure electronic' pressure-induced shifts (PS's) and the PS's due to electron-phonon interaction (EPI) of the R1, R2, B1, B2, B3, and R3' lines and the ground-state zero-field-splitting of ruby have been uniformly calculated. The calculation results are in very good agreement with all the experimental data. At normal pressure, ruby is a crystal with very strong crystal field. Thus, the admixture of |t22 (3T1)e4T2) and |t232E) bases in the wavefunction of R1 level of ruby is small at normal pressure, and it gradually decreases with increasing pressure, which causes the R1-line PS of ruby to monotonously red shift with approximate linearity. The combined effect of the pure electronic PS of R1 line and the PS of R1 line due to EPI gives rise to the total PS of R1 line. The analyses and comparisons among the features of R1-line PS's of three laser crystals (ruby, GSGG:Cr3+ and GGG:Cr3+) have been made, and the origin of their difference has been revealed.