Electronic and optical properties of C and Nb co-doped anatase TiO2

The electronic and optical properties of C, C–Nb and C–2Nb doped anatase TiO2 are studied using the first principles calculations. For the C-doped TiO2, three subbands in the band gap are generated due to the C-2p states, which suppress the effective band gap for electron transfer, while the gap states are partially occupied and probably serve as the recombination centers for electrons and holes. Therefore, the C–2Nb co-doping is investigated for the charge compensation consideration. Two possible co-doping configurations are comprehensively studied and compared. The three subbands in the band gap of the C mono-doped TiO2 become fully occupied because the two Nb atoms contribute sufficient electrons for compensation. Furthermore, the optical properties of the co-doped TiO2 and pure TiO2 are calculated. It is found that the optical absorption of the C–2Nb co-doped TiO2 extends its coverage over the visible light region.