Determination of the electron–phonon coupling parameters from the thermal shifts of R-lines for Cr3+-doped garnets

Abstract

The thermal shifts of R1 and R2 lines of Cr3+-doped garnets Y3Ga5O12 (YGG), Y3Sc2Al3O12 (YSAG) and Gd3Sc2Al3O12 (GSAG) are studied by considering both the static contribution (which is frequently neglected in the previous papers) due to lattice thermal expansion and the vibrational contribution due to electron–phonon interaction. In the studies, the static contribution is calculated with the thermal expansion coefficient of the corresponding cluster in the host garnet crystals. The results indicate that the static contributions in sign are opposite to and in magnitude are about 10% of the corresponding vibrational contributions. The true electron–phonon coupling parameters α′ obtaining by taking both contributions into account increase more than 10% in comparison with the corresponding apparent electron–phonon coupling parameters α determined by considering only the vibrational contribution in the previous paper. So, to obtain the complete understanding of thermal shift of a spectral line and the true rather than apparent electron–phonon coupling parameters, one should take account of both the static and vibrational contributions.