Structural, electronic and optical properties of S-doped, Sc-doped and Sc-S co-doped anatase TiO2: a DFT + U calculation

Defect formation energies, electronic structures and optical properties of non-metal S, lanthanide metal Sc-doped and Sc-S co-doped anatase TiO2 were systematically investigated via a GGA + U method based on density functional theory (DFT). The on-site Coulomb corrections were applied to both 3d orbitals of Ti atom (U-Ti_3d) and 2p orbitals of O atom (U-O_2p). The results show all doped TiO2 systems exhibit a certain degree of red-shift due to the presence of impurity levels in the bandgap; in particular, the S-doped and Sc-S co-doped TiO2 exhibit better light absorption properties in the visible light range than either pure or Sc-doped TiO2. In addition, the positive synergistic effect between the Sc and S atoms not only expands the absorption edge, but also increases the light absorption coefficient in the visible region. As a result, the Sc-S co-doped anatase TiO2 shows the best optical absorption spectrum in all doping systems.