Investigation of temperature-dependent optical properties of TiO2 using diffuse reflectance spectroscopy

Temperature-dependent diffuse reflectance spectroscopy (DRS) measurements have been carried out on the polycrystalline sample TiO2. Important values from optical parameters such as band gap (Eg), Urbach energy (EU), and Urbach focus (E0) have been estimated in the range of 300–450 K. In order to understand the experimental value of band gap (Eg) of TiO2, i.e., obtained from DRS, a first-principle calculation has been performed. The dependency of EU and the slope of exponential tails (β1, β2) of the density of states has also been studied which determines the distribution of exponential tails near the valence and conduction bands in semiconducting oxides. The behavior of optical band gap and EU has also been investigated with the influence of temperature using Cody model. From the temperature dependence of band gap measurements, the value of thermodynamical parameter such as Debye temperature (θD) has also been estimated. Thus it appears that the temperature-dependent optical absorption spectroscopy is very powerful and economical tool to probe the electronic structure near band edge and also to estimate the important thermodynamical parameter.