Mixed alkali effect in Cu2+ doped boroarsenate glasses—EPR and optical absorption studies

The local structure around Cu2+ ion has been examined by means of electron paramagnetic resonance and optical absorption measurements in xK2O–(40−x)Na2O–50B2O3–10As2O3 (0⩽x⩽40) glasses. The site symmetry around Cu2+ ions is found to be tetragonally distorted octahedral and the ground state of Cu2+ is dx2-y2dx2-y2. The spin-Hamiltonian parameter g|| goes through a minima whereas A∥A∥ goes through a maxima around RK=0.5, showing the mixed alkali effect. The glass exhibited broad absorption band centred 12,239 cm−1 corresponding to the transition 2B1g→2B2g. By correlating the EPR and optical absorption data, the molecular orbital coefficients α2 and β12 are evaluated for the present glass system. The IR studies show that the glass system contains BO3 and BO4 units in the disordered manner.