First-principles calculation of nitrogen-tungsten codoping effects on the band structure of anatase-titania

The electronic properties and photocatalytic activity of nitrogen (N) and/or tungsten (W)-doped anatase are calculated using density functional theory. For N-doping, isolated N 2p states above the top of the valence band are responsible for experimentally observed redshifts in the optical absorption edge. For W-doping, W 5d states below the conduction band lead to band gap narrowing; the transition energy is reduced by 0.2 eV. Addition of W to the N-doped system yields significant band gap narrowing gap by 0.5 eV. This rationalizes recent experimental data which showed that N/W-doped titania exhibits higher visible-light photocatalytic efficiency than either N- or W-doping alone.