Electrical and spectroscopic properties of LiF–Bi 2O 3–P 2O 5:TiO 2 glass system

Abstract

LiF–Bi 2O 3–P 2O 5 glasses mixed with different concentrations of TiO 2 (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 Ti 3+ and Ti 4+ states and redox ratio increases with increase in the concentration of TiO 2 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 O 2− ion in to empty 3d orbital of substitutionally positioned octahedral Ti 4+ ions where as the NIR band is attributed to Bi 5+ transitions. The optical absorption and luminescence studies have also indicated the presence of bismuth ions in Bi 5+ state in addition to Bi 3+ 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 TiO 2 up to 2.0 mol%. The analysis of the results of D.C. conductivity has indicated that in the region T > θ D/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 TiO 2 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.