EPR and optical absorption studies of VO 2+ ions in alkaline earth aluminoborate glasses

Abstract

Electron paramagnetic resonance (EPR) and optical absorption studies have been carried out for VO 2+ ions in calcium aluminoborate glasses. The EPR spectra of all the glass samples exhibit resonance signals, characteristic of VO 2+ ions. The values of spin-Hamiltonian parameters indicate that the VO 2+ ions in calcium aluminoborate glasses were present in octahedral co-ordination with a tetragonal compression and belong to C 4v symmetry. The number of spins ( N) participating in resonance was calculated as a function of concentration as well as temperature. It is observed that variation of N with temperature obeys the Boltzmann law. From the EPR data, the paramagnetic susceptibility ( χ) is calculated at various temperatures and the Curie constant ( C) was evaluated from the 1/ χ– T graph. The Fermi contact interaction parameter ( k), dipolar hyperfine coupling parameter ( P) have been calculated and these values are found to be independent of V 2O 5 content and temperature. The optical absorption spectrum exhibits two bands corresponding to the d–d transition 2B 2g → 2E g and 2B 2g → 2A 1g in the order of increasing energy. The theoretical values of optical basicity ( Λ th) of the glasses have also been evaluated.