Optical properties and photocatalytic activity of nanocrystalline TiO$_2$ doped by 3d-metal ions

The influence of impurities on optical and photocatalytic properties was studied in a series of nanocrystalline TiO$_2$ with similar coherent scattering region sizes, phase compositions, surface areas and lattice parameters doped by Fe, Cr, Mn and V ions. Doping leads to an increase of absorption in the visible part of the spectrum due to the formation of additional levels in the band gap. In the case of Fe and Cr ions, d-d transitions are observed, whereas in the case of Mn and V ions, an additional band is associated with the transition from impurity level to $E_c$. The presence of impurities effectively suppresses photocatalytic activity in the methyl orange decoloration reaction.