Energy Spectrum of La3Lu2Ga3O12:Cr3+ and Its Pressure-Induced R-Line-Shift Reversal

By means of both the theory for pressure-induced shifts (PS) of energy spectra and the theory for shifts of energy spectra due to electron-phonon interaction (EPI), the normal-pressure energy spectra of α and β centers of Cr3+ ions for LLGG:Cr3+ and the PS's of R1 lines and U band of these centers have been calculated at 10 K, respectively. The total calculated results are in very good agreement with the experimental data. For LLGG:Cr3+, the pressure-induced low-high crystal-field transition and the reversal of R1-line PS take place. The pressure-dependent variation of Rmixel (2E-4T2) [mixing-degree of |t22(3T1)e4T2 ) and |t232E) base-wavefunctions in the wavefunction of R1 state without EPI] plays a key role for the reversal of R1-line PS. The behavior of the pure electronic PS of R1 line is quite different from that of the PS of R1 line due to EPI. It is the combined effect of them that gives rise to the total PS of R1 line. The comparison between R1-line PS's of GSGG:Cr3+ and LLGG:Cr3+ has been made. It is found that a peak of R1-line PS appears at Rmixel (2E-4T2) ∼ 0.08.