Electron–phonon coupling of Cr3+ doped garnets

Abstract

The electron–phonon coupling for the 2E→4A2 transition on Cr3+ has been determined for different chromium doped garnets by measuring the ratio between vibronic and zero-phonon line intensity, and by performing temperature dependent line broadening and line shift measurements. It was found that the electron–phonon coupling for the transition is dependent on the covalency of the host lattice: due to the difference in covalency the electron–phonon coupling for a gallate lattice (e.g. Y3Ga5O12) is higher than the aluminate lattice (e.g. Y3Al5O12).Measurements on the dependence of electron–phonon coupling on the size of the site for which Cr3+ substitutes indicate that the value of the electron–phonon coupling parameter α (determined from temperature dependent line shift measurements) is lower for garnets where Cr3+ resides in the smaller Ga3+- and Al3+-sites (e.g. Y3Al5O12 and Y3Ga5O12) than for the garnets with Cr3+ on a bigger Sc3+-site (e.g. Y3Sc2Al3O12 and Gd3Sc2Al3O12).