Thermal shifts and electron-phonon coupling parameters for Cr3+-doped Lu3Al5O12 and Lu3Ga5O12 garnet crystals

A full expression containing the vibrational contribution due to electron-phonon interaction and the static contribution due to lattice thermal expansion is employed to study the thermal shifts of R-line (corresponding to 2E→4A2 transition) for Cr3+-doped Lu3Al5O12 (LuAG) and Lu3Ga5O12 (LuGG) garnet crystals. The results indicate that the vibrational contribution results in the thermal red-shift, whereas the static contribution results in the thermal blue-shift. The magnitude of static contribution is nearly 14% that of the vibrational contribution, which leads the obtained true electron-phonon coupling parameter α′ to increase about 16% in comparison with the apparent electron-phonon coupling parameter α obtained by a simple expression including only the vibrational contribution. So, for reasonably describing the thermal shift and giving the true electron-phonon coupling parameter for a spectral line in crystals, one should adopt the full expression. The electron-phonon coupling parameter α′ in LuAG: Cr3+ is smaller than that in LuGG: Cr3+. The outcomes are discussed.