Theoretical study of the local structures and the EPR parameters for RLNKB glasses with VO2+ and Cu2+ dopants

The electron paramagnetic resonance (EPR) parameters and local structures for impurities VO2+ and Cu2+ in RO-Li2O-Na2O-K2O-B2O3 (RLNKB; R = Zn, Mg, Sr and Ba) glasses are theoretically investigated by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral 3d(1) and tetragonally elongated octahedral 3d(9) clusters, respectively. The VO2+ and Cu2+ dopants are found to undergo the tetragonal compression (characterized by the negative relative distortion ratios rho approximate to -3%, -0.98%, -1% and -0.8% for R = Zn, Mg, Sr and Ba) and elongation (characterized by the positive relative distortion ratios rho approximate to 29%, 17%, 16% and 28%), respectively, due to the Jahn-Teller effect. Both dopants show similar overall decreasing trends of cubic field parameter D-q and covalency factor N with decreasing electronegativity of alkali earth cation R. The conventional optical basicities Lambda(th) and local optical basicities Aloe are calculated for both systems, and the local Lambda(loc) are higher for Cu2+ than for VO2+ in the same RLNKB glass, despite the opposite relationship for the conventional Ath. This point is supported by the weaker covalency or stronger ionicity for Cu2+ than VO2+ in the same RLNKB system, characterized by the larger N in the former. The above comparative analysis on the spectral and local structural properties would be helpful to understand structures and spectroscopic properties for the similar oxide glasses with transition-metal dopants of complementary electronic configurations.