EPR and optical studies on binary mixed alkali-alkaline earth oxide borate glasses doped with Cu2+ ions |
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Authors: | G. Srinivas J. Siva Kumar Md. Shareefuddin M. N. Chary R. Sayanna |
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Affiliation: | 1.Department of Physics,Osmania University,Hyderabad, Telangana state,India |
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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 (T g ). 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 (E opt) 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 β 1 2 were evaluated. |
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