Structural, electronic and optical properties of La, C-codoped TiO2 investigated by first principle calculations

The electronic structures and optical properties of La, C-codoped TiO2 were investigated by the first-principles plane-wave ultrasoft pseudopotential method. Our calculations suggest that the micro-structures of La-C codoped system is different from that of TiO2, and the hole effective mass is increased by La-doping, which can create holes in the valence band; Nonmetal C doping can narrow the band gap of TiO2 and enhance the photo-catalytic activity by the formation of localized mid-gap state originated from C 2p states above the top of the valence band; Metal La and nonmetal C co-doping could induce a synergistic effect, the doping of La atoms leads the redistribution of C 2p states in C atoms, which provide more electrons to participate into the 3d states of Ti atoms. The charge compensation effects between Ti 3d and C 2p produce impurity levels, which reduce the band gaps and enhance the carrier concentration, meanwhile La ions are not easy to enter the lattice of TiO2, which may form hetero-junction structure of La2O3-TiO2 with better dispersion in the bulk phase of TiO2 to limit the recombination of photo-generated electron hole pairs. The calculated results of optical properties show that C-TiO2 and La-C-TiO2 systems exhibit good visible absorption and the doping is beneficial to the propagation of light in the doped TiO2.