Electron paramagnetic resonance, optical and electrical properties of vanadyl doped alkali germanoborate glasses

Glasses with composition xGeO2.(0.30−x)M2O.0.70B2O3 (M=Li, K) containing 2.0 mol% of V2O5 have been prepared in the range 0.00≤x≤0.15 by normal melt quenching method. Electron paramagnetic resonance (EPR), optical transmission and absorption spectra and dc conductivity of these glasses have been studied. Spin Hamiltonian parameters (SHPs) of VO2+ ions, dipolar hyperfine coupling parameter, P, Fermi contact interaction parameter, K and molecular orbital coefficients (α2 and γ2) have been calculated. In GeO2·Li2O·B2O3 glasses there is no change in the tetragonality of the V4+O6 complex and the size of 3dxy orbit also remains unchanged with increase in GeO2 content. In GeO2·K2O·B2O3 glasses, there is an increase in the tetragonality of the V4+O6 complex and the 3dxy orbit expands with increase in GeO2 content. Values of the theoretical optical basicity, Λth, have also been reported. Optical band gap decreases with increase in GeO2 content. The dc conductivity of these glasses decreases and the activation energy increases with increase in GeO2:M2O ratio.