Electron paramagnetic resonance and optical absorption studies of Cu2+ spin probe in MgO–Na2O–B2O3 ternary glasses

Electron paramagnetic resonance and optical absorption studies of MgO–Na2O–B2O3 glasses were made by introducing Cu2+ as a spin probe. The electron paramagnetic resonance spectra of all the glass samples recorded at X-band frequencies have similar spectral features. It is observed that the spin-Hamiltonian parameters calculated from the EPR spectra are influenced by the glass composition. The Cu2+ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu2+ is dx2−y2 orbital (2B1g) and the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d–d transition bands of Cu2+ ion. The bond parameters indicate a slight covalency for the σ and in-plane π-bonds, compared to the out-of-plane π-bonds. The theoretical optical basicity parameter values were evaluated and it was observed that τπ which is a measure of Lewis basicity of non-bridging oxide ions in the glasses varies in a non-linear manner with increasing optical basicity.