EPR and optical studies on binary mixed alkali-alkaline earth oxide borate glasses doped with Cu2+ ions

Abstract

Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li2O–xK2O–12.5BaO–12.5MgO–49B2O3–1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X-ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calorimetry (MDSC) was used to determine the glass-transition temperature (Tg). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramagnetic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of \(C{u^{2 + }}is{\kern 1pt} {d_{{x^2} - {y^2}}}\) orbital (2B1g) and the site symmetry around Cu2 is tetragonally distorted octahedral. The variation of g|| and A|| as a function of Li2O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu2 ions corresponding to 2B1g → 2B2g transition. From the optical absorption studies the values of the optical band gap (Eopt) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α2, β2 and β12 were evaluated.