Band-gap energy estimation from diffuse reflectance measurements on sol-gel and commercial TiO2: a comparative study

A comparison of the band gap energy estimated from UV-vis reflectance spectra of TiO2 powders prepared by sol-gel route versus commercial TiO2 powders, nanopowder, bulkpowder and P25 is reported. The experimental results obtained from the optical absorption spectra were reported for all the TiO2 samples. Graphic representations were used to calculate E-g: absorbance versus lambda; F(R) versus E; (F(R) h nu)(n) versus E, with n = A1/2 for an indirect allowed transition and n = 2 for a direct allowed transition. From the results, it could be seen that E-g strongly varied according to the equation used for the graphic representation. Differences in E-g up to 0.5 eV for the same semiconductor depending on the transition chosen were observed. Accurate E-g estimation in the four semiconductors studied was obtained by using the general equation alpha (h nu) a parts per thousand B (h nu - E-g)(n) (where alpha similar to F(R)) and indirect allowed transition.