Theoretical study of the local distortions and the EPR parameters for VO2+ and Cu2+ centers in oxyfluoroborate glasses

Abstract

Theoretical calculations of the local structures and the electron paramagnetic resonance (EPR) parameters for the impurities VO2+ and Cu2+ centers in oxyfluoroborate glasses (OFG) were performed by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral [VO6]8- and tetragonally elongated octahedral [CuO6]10− clusters, respectively. In the calculations, the required crystal-field (CF) parameters are estimated from the superposition model which enables correlation of the CF parameters and hence the EPR parameters with the tetragonal distortion (characterized by the relative tetragonal elongation (or compression) ratio τ along the C4 axis) of [VO6]8- (or [CuO6]10−) cluster. Based on the calculations, the [VO6]8- and [CuO6]10− clusters are found to undergo the tetragonal compression (τ ≈ 1.7%) and elongation (τ ≈ 2.9%) along the C4 axis, the signs of A|| and A⊥ for VO2+ and Cu2+ centers in OFG were also determined. The above theoretical approach on local structural properties would enhance the understanding of the structural properties for other oxide glasses with transition-metal (TM) dopants.