Self-Trapped Charge Carriers in Defected Amorphous TiO2

Self-trapped polarons and excitons associated with defects can localize energy in ways that can modify the material properties. The doped amorphous titanium dioxide (aTiO(2)) that possesses self-trapped polarons and excitons due to its inherited disorder and extrinsic doping has recently drawn increased attention as potential cheap visible light photocatalyst. However, the synergetic role that intrinsic and extrinsic defects play in enhancing the photoactivity of doped aTiO(2) is still a mystery. To gain insights into the photocatalytic behavior of defected aTiO(2), in this study, we analyzed three Fe-doped aTiO(2) models having Fe in Fe(II), Fe(III), and Fe(IV) oxidation states. The density functional theory with Hubbard energy correction (DFT+U) calculations conducted in this study clearly indicate that the visible light absorption of aTiO(2) will be improved by doping it with Fe. Furthermore, our investigation reveals that even though all the doped aTiO(2) models showed highly localized states at mid gap and band edges, doping with Fe(II) led to maximum visible light absorption. This distinct behavior of Fe(II)-doped aTiO(2) is attributed to the unique position of its mid gap states, high self-trap energy, low mobility, and weak chemical bonds.