EN
The aim of the present study is to explain the local distortion around Cr^{3+} ions doped in the title crystal using the latest experimental data regarding optical and EPR spectra. We calculated g_ǁ, g_⊥, and D spin-Hamiltonian parameter as function of angle between the C_3 axis and metal-ligand chemical bond in local distorted octahedral cluster [CrO_6]^{9-} formed after doped crystal. The method is based on the single spin-orbit coupling parameter model, in the cluster approach using Macfarlane high order perturbation formulae. The results compared with experimental data give a reasonable agreement.