VO 2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques

Abstract

Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO–PbO–B 2O 3) glass system have been studied. 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 zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C 4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V 2O 5 content and temperature but changing with ZnO content. The decrease in Δ g ∥/Δ g ⊥ value with increase in ZnO content indicates that the symmetry around VO 2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V 2O 5 is attributed to a fall in the ratio of the number of V 4+ ions ( N 4) to the number of V 5+ ions ( N 5). The number of spins ( N) participating in resonance was calculated as a function of temperature for VO 2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/ χ– T graph. The optical absorption spectra show single absorption band due to VO 2+ ions in tetragonally distorted octahedral sites.