Density functional characterization of C-doped anatase TiO2 with different oxidation state

The electronic structures of carbon doped anatase TiO2 with different oxidation state were investigated in this paper. The influences of the dopant on the crystal structure, the energy gap, the charge density, and the optical properties were discussed by using first-principle calculations based on the density functional theory (DFT). The C 2p impurity states, which lie between the conduction band and the valence band in both C & O and C2- & O doped TiO2, play as springboard, permitting electron transition, transferring charge, and leading to separation of electron-hole pair and electron delocalization. It results in reduction of the energy gap and the optical absorption edge shifting to the red light regime. With the formation of CO3 unit in C & Ti doped TiO2, the charge density is modified substantially and the energy gap vanishes. The electrons are dispersive in the whole crystal lattice, with the crystal phase transition from semiconductor to metal conductor. However, electrons in the impurity states become more localized for C4+ & Ti doped TiO2, with the energy gap (E-g) broadening and the absorption edge shifting to the blue light regime. It indicates from theoretical aspect that the modification effect on electronic structures and properties is according to different oxidation state of the dopant. Some practical definite functional materials could be obtained by doping with chemical treatment. (C) 2010 Elsevier B.V. All rights reserved.