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

Abstract

The local structure around Cu 2+ ion has been examined by means of electron paramagnetic resonance and optical absorption measurements in x K 2 O–(40− x )Na 2 O–50B 2 O 3 –10As 2 O 3 (0⩽ x ⩽40) glasses. The site symmetry around Cu 2+ ions is found to be tetragonally distorted octahedral and the ground state of Cu 2+ is d x 2 - y 2 . The spin-Hamiltonian parameter g || goes through a minima whereas A ∥ goes through a maxima around R K =0.5, showing the mixed alkali effect. The glass exhibited broad absorption band centred 12,239 cm −1 corresponding to the transition 2 B 1g → 2 B 2g . By correlating the EPR and optical absorption data, the molecular orbital coefficients α 2 and β 1 2 are evaluated for the present glass system. The IR studies show that the glass system contains BO 3 and BO 4 units in the disordered manner.