Pressure Effects on Spectra of Tunable Laser Crystal GSGG： Cr^3＋ IV： Pressure—Induced Shifts of R1 Line, R2 Line, and U Band at 300 K

By means of both a theory for pressure-induced shifts (PS) of energy spectra and a theory for shifts of energy spectra due to electron-phonon interaction (EPI), the 'pure electronic' PS and the PS due to EPI of R1 line, R2 line, and U band of GSGG:Cr3+ at 300 K have been calculated, respectively. The calculated results are in good agreement with all the experimental data. Their physical origins have also been explained. It is found that the mixing-degree of and base-wavefunctions in the wavefunctions of R1 level of GSGG:Cr3+ at 300 K is remarkable under normal pressure, and the mixing-degree rapidly decreases with increasing pressure. The change of the mixing-degree with pressure plays a key role not only for the 'pure electronic' PS of R1 line and R2 line but also the PS of R1 line and R2 line due to EPI. The pressure-dependent behaviors of the 'pure electronic' PS of R1 line (or R2 line) and the PS of R1 line (or R2 line) due to EPI are quite different. It is the combined effect of them that gives rise to the total PS of R1 line (or R2 line). In the range of about 15 kbar ~ 45 kbar, the mergence and/or order-reversal between levels and levels take place, which cause the fluctuation of the rate of PS for with pressure. At 300 K, both the temperature-dependent contribution to R1 line (or R2 line or U band) from EPI and the temperature-independent one are important.