“…This model allows one to analyse the absorption and emission band shapes and the transition probabilities between the ground and the excited states. Furthermore, the Cr 3+ site distribution can be taken into account in this model [4,7,8,11,14,[16][17][18]. In some works [4,8,11] an harmonic approximation with linear electron-lattice coupling between the ground and the excited levels has been considered, with site-to-site changes in the octahedral crystal-field parameter 10 Dq or equivalently, in the zero-phonon energy parameter O (see Fig.…”