Band gap narrowing of titanium dioxide by sulfur doping

Umebayashi, Tsutomu; Yamaki, Tetsuya; Ito, Hisayoshi; Asai, Keisuke*

Titanium dioxide (TiO) doped with sulfur (S) was synthesized by oxidation annealing of titanium disulfide (TiS). According to the X-ray diffraction patterns, TiS turned into anatase TiO when annealed at 600 C. The residual S atoms occupied O-atom sites in TiO to form Ti-S bonds. The S doping caused the absorption edge of TiO to be shifted into the lower energy region. Based on the theoretical analyses using ab-initio band calculations, mixing of the S 3p states with the valence band was found to contribute to the band gap narrowing.