Density Functional Theory Studies of Doping in Both Bulk- and Surface-State Titania

The structural, energetic and electronic properties of substitutional Ge, N/W, Bi/S (co)doped bulk anatase-titania systems have been investigated, along with those of a range of adsorptive and substitutional S- and P-doped rutile-titania (110) surfaces, by first-principles density functional theory (DFT) calculations. The stability of the various doping configurations was compared on the basis of their calculated formation/adsorption energies, and preferred dopant states were identified and characterised in terms of structural features. In many cases, red-shifts in optical absorption edge and reductions in photon transition energy were observed, along with synergistic effects between electronic states introduced by co-dopants. These observations have been used to rationalise various recent experimental observations under these dopant conditions.