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

Electron paramagnetic resonance and optical absorption studies of MgO-Na2O- B2O3 glasses were made by introducing Cu2+ as a spin probe. The electron pa ramagnetic resonance spectra of all the glass samples recorded at X-band fr equencies have similar spectral features. It is observed that the spin-Hami ltonian parameters calculated from the EPR spectra are influenced by the gl ass composition. The Cu2+ ions are in well-defined axial sites but subjecte d to small distortion leading to the broadening of the spectra. The spin-Ha miltonian parameter values indicate that the ground state of Cu2+ is d(x2-y 2) orbital (B-2(1g)) and the site symmetry around Cu2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad ban d corresponding to the d-d transition bands of Cu2+ ion. The bond parameter s indicate a slight covalency for the sigma and in-plane pi -bonds, compare d to the out-of-plane pi -bonds. The theoretical optical basicity parameter values were evaluated and it was observed that tau (pi) which is a measure of Lewis basicity of non-bridging oxide ions in the glasses varies in a no n-linear manner with increasing optical basicity. (C) 2000 Elsevier Science B.V. All rights reserved.