Probing electronic transitions and defect-induced Urbach tail bands in functional oxides using diffuse reflectance spectroscopy and the Kubelka-Munk function

Abstract This work explores electronic transitions and defect-induced Urbach tail bands in functional oxides (V 2 O 5 , BaSnO 3 , PbZr 0.52 Ti 0.48 O 3 , BiMnO 3 , and BiFeO 3 ) using diffuse reflectance spectroscopy assisted by the Kubelka–Munk function, Tauc plot, and first derivative of the reflectance. It is found that BiMnO 3 has an indirect electronic transition at the band edge, while other oxides show direct band gap interband transitions. For the direct band gap materials, the estimated Urbach energy ( E U ) values due to defects ranged between 0.24–0.48 eV. Moreover, the band gap energy of the multiferroic BiFeO 3 was reduced by the induced chemical pressure and a decrease in particle size. To highlight the applications of the multiferroic BiFeO 3 in optoelectronic devices, an electronic band diagram has been unveiled.