Optical characteristics of TeO2-boro bismuthate thin films based only on their reflectance spectra

Abstract

In the current investigation, homogenous thin films from TeO2-boro-bismuthate glasses are synthesized by the thermal evaporation process. The film reflectivity, R(λ), was measured within the 0.22−2.5μm spectral range. The complex refractive index (nˇ=n+ik) and the film thicknesses were estimated with high accuracy. The increment of TeO2 was found to increase the optical gap (Eg) values, whereas the refractive index (n) decreased. The dispersion of n was explained following the Wemple–DiDomenico model. The absorption mechanism in the explored films was found to obey the allowed indirect optical transition rule. The Eg compositional dependence is analyzed based on the Tauc's slope B0.5 and the width of the localized states, which decreased with increasing TeO2 content. The other optical parameters, such as dielectric loss, the plasma frequency, dissipation factor, as well as the optical conductivity of the films, were estimated.