Use and misuse of the Kubelka-Munk function to obtain the band gap energy from diffuse reflectance measurements

The determination of the optical band gap energy (E-g) is important for optimization of the generation of electron/hole pairs in semiconductor materials under illumination. For this purpose, the classical theory proposed by Kubelka and Munk (K-M) has been largely employed for the study of amorphous and polycrystalline materials. In this paper, the authors demonstrate, step by step, how to use the K-M function and apply it thoroughly to the determination of the E-g of TiO2 semiconductor powder (pressed at different thicknesses) from diffuse reflectance spectroscopy (DRS) measurements. For the sample thicknesses 1-4 mm, E-g values of 3.12-3.14 eV were obtained. With this work it is envisaged a clarification to the procedure of determination of the E-g from the K-M theory and DRS data, since some drawbacks, and misconceptions have been identified in the recent literature. In particular, the widely used practice of determining the E-g of a material directly from the K-M function is found to be inadequate.

Automated summary

The authors demonstrate how to use the K-M function and apply it to determine the E-g of TiO2 semiconductor powder, highlighting drawbacks and misconceptions in the procedure of E-g determination from the K-M theory and DRS data, emphasizing that directly determining E-g from the K-M function is inadequate.