Electrical and spectroscopic properties of LiF–Bi2O3–P2O5:TiO2 glass system

LiF–Bi2O3–P2O5 glasses mixed with different concentrations of TiO2 (ranging from 0.5 to 3.0 mol%) were prepared. D.C. conductivity and dielectric properties over a range of temperature and also optical absorption, luminescence, ESR and IR spectral studies have been investigated. The optical absorption and ESR studies have indicated that the titanium ions exist in Ti3+ and Ti4+ states and redox ratio increases with increase in the concentration of TiO2 up to 2.0 mol%. The luminescence spectra exhibited two broad emission bands one in the wavelength region 450–600 nm and the other in the NIR region. The band in the visible region is identified due to the charge transfer from O2− ion in to empty 3d orbital of substitutionally positioned octahedral Ti4+ ions where as the NIR band is attributed to Bi5+ transitions. The optical absorption and luminescence studies have also indicated the presence of bismuth ions in Bi5+ state in addition to Bi3+ state. The IR spectral studies have indicated that there is a growing degree of disorder in the glass network with increase in the concentration of TiO2 up to 2.0 mol%. The analysis of the results of D.C. conductivity has indicated that in the region T > θD/2, the small polaron hopping model fits well and the conduction is adiabatic in nature. These results further indicated that there is a mixed conduction (both ionic and electronic) and the ionic conduction seems to prevail over polaron hopping in the glasses containing TiO2 more than 2.0 mol%. The variations of dielectric constant and loss with temperature have been analyzed on the basis of space charge polarization based on the results of the spectroscopic studies.