Characterization and optical absorption studies of VO2+:Li2O-K2O-Bi2O3-B2O3 glass system

Mixed alkali bismuth borate glasses xLi2O-(30 - x) K2O-10Bi2O3-55 B2O3 (0 < x < 30) doped with 5 mol% vanadium ions were prepared from the melts. These glasses were characterized using X-ray diffraction, differential scanning calorimetry and density measurements. Optical absorption studies were carried out as a function of alkali content to look for mixed alkali effect (MAE) on the spectral properties of these glasses. From the study of ultraviolet absorption edge, the optical band gap energies and Urbach energies were evaluated. The average electronic polarizability of the oxide ion, optical basicity and the interaction parameters were also evaluated for all the glasses. Many of these parameters vary non-linearly exhibiting a minima or maxima with increasing alkali concentration, indicating the mixed alkali effect. An attempt is made to interpret MAE in this glass system in terms of its glass structure.