Electronic properties of N- and C-doped TiO2

We present first-principles density-functional calculations for the electronic properties of nitrogen(N)-doped as well as carbon(C)-doped titanium dioxide (TiO2). We find that the bands originating from N (C) 2p states appear in the band gap of TiO2, but the mixing of N (C) with O2p states is too weak to produce a significant band-gap narrowing. Our results are consistent with several recent experimental data of N-doped TiO2, where the absorption of visible light is due to isolated N2p states above the valence-band maximum of TiO2 rather than due to a band-gap narrowing.