A theoretical study of concentration-dependent xCaF2-20TeO2-(79‒x)Na2B4O7-CuO glass: Local distortions, EPR parameters and optical properties

The electron paramagnetic resonance parameters (EPR) and local structure properties of the Cu 2+ center in xCaF 2 –20TeO 2 -(79-x)Na 2 B 4 O 7 -CuO glasses are theoretically studied based on the high-order perturbation formulae of a 3d 9 ion in a tetragonally elongated octahedron. Determined from the best fitted piecewise linear function (the reverse point at 40 mol%), the corresponding overall varying tendencies and fluctuations of local distortions, EPR parameters and optical properties are reproduced, which can be ascribed to the generated non-bridging oxygen's. The microscopic mechanisms of the above concentration dependences for these quantities are illustrated from the transformation of BO 3 and TeO 3 units. Meanwhile, the electronic properties are obtained through the covalence parameters N and the decrease optical basicity, which both mean the decreasing covalency of the whole glass systems and strong ionicity around Cu 2+ .