Investigations of the optical and EPR data and local structure for the trigonal tetrahedral Co2+ centers in LiGa5O8: Co2+ crystal

In this paper, we calculate uniformly the optical and EPR data for Co2+ ion at the trigonal tetrahedral Ga3+ site in LiGa5O8 crystal from the complete diagonalization (of energy matrix) method founded on the two-spin-orbit-parameter model, where the contributions to the spectroscopic data from both the spin-orbit parameter of dn ion (in the classical crystal field theory) and that of ligand ions are contained. The calculated ten spectroscopic data (seven optical bands and three spin-Hamiltonian parameters g//, g⊥ and D) with only four adjustable parameters are in good agreement with the available observed values. Compared with the host (GaO4)5− cluster, the great angular distortion and hence the great trigonal distortion of (CoO4)6− impurity center obtained from the calculations are referred to the large charge and size mismatch substitution. This explains reasonably the observed great g-anisotropy Δg (= g// − g⊥) and zero-field splitting D for the (CoO4)6− cluster in LiGa5O8: Co2+ crystal.