Theoretical studies of the local structure and the epr parameters for tetragonal Cu2+ center in mixed alkali cadmium phosphate glasses

Abstract: The local structure of the Cu2+ center in mixed alkali cadmium phosphate (10Li2O-10Na2O-20CdO-59.5P2O5) glass is theoretically investigated from the optical spectral data and high-order perturbation formulas of the electron paramagnetic resonance (EPR) parameters (g-factors g║,g┴ and the hyperfine structure constants A║,A┴ ) for a 3d9 ion in a tetragonally elongated octahedron. In these formulas, the ligand orbital and spin-orbit coupling contributions are taken into account based on the cluster approach in view of moderate covalency. The required crystal-field parameters are determined by the superposition model. According to the calculations, the impurity-ligand distances parallel and perpendicular to the C4 axis of [CuO6] 10- cluster are found to be, respectively, R ║ ≈2.051 Å and R ┴ ≈ 2.029 Å due to Jahn-Teller effect. Based on the above local structure data, the optical spectra are satisfactorily interpreted. The signs of A║ and A┴ for the Cu 2+ center are suggested in the discussion.