Research on the thermal red-shift of R-line for K2Ge4O9: Mn4+ crystal

The thermal red-shift of R-line (2E-4A2 transition) for K2Ge4O9: Mn4+ crystal is investigated by considering the competition between the static contribution due to lattice thermal expansion and the vibrational contribution due to electron-phonon interaction. It is found that with the growing temperature, the static contribution results in the blue-shift of R-line, whereas the vibrational contribution leads to the red-shift. The static contribution in magnitude is much smaller than the vibrational contribution. So, the observed red-shift of R-line with the increasing temperature for K2Ge4O9: Mn4+ crystal is due to the dominant vibrational contribution rather than the opposite changes of Racah parameters B and C with temperature based on only the static contribution suggested previously.