Electron paramagnetic resonance and optical absorption spectra of Cu²⁺ ions in alkali barium chlorophosphate glasses

The results of measurement of electron paramagnetic resonance and optical absorption spectra at room temperature of alkali barium chlorophosphate glasses (BaCl₂-M₂O-P₂O₅) doped with 1 mol% CuO are presented for various alkali compositions (M = Li, Na, K, Li-Na, Na-K and K-Li). The results indicate that the mixed alkalies do not produce alterations of the glass network. The ground state of Cu²⁺ is the d〈x2-y2〉 orbital and the site symmetry that exists around the Cu²⁺ ions is octahedral with a tetragonal elongation. The theoretical optical basicity of the glasses have been evaluated and the changes in optical basicity are independent of changes in spin-Hamiltonian parameters of the Cu²⁺. The optical absorption spectra of Cu²⁺ ions for all the glass samples was single asymmetric band which corresponds to a ²B_1g → ²B_2g transition. By correlating the spectral data, the molecular orbital coefficients α² and β²₁ for Cu²⁺ have been evaluated and results indicate that there is covalency for the in-plane σ-bonding and that the in-plane π-bonding is significantly ionic in nature.