Photocatalytic, spectroscopic and transport properties of lanthanide-doped TiO2 nanocrystals

The photocatalytic properties of the anatase form of nanocrystalline TiO2 doped with lanthanide ions (Eu3+, Sm3+ and Er3+), obtained by a sol-gel preparation method, are studied by means of the degradation of methylene blue. It is observed that the presence of Sm3+ ion as a dopant significantly improves the photocatalytic activity of anatase TiO2 with respect to the Eu3+ or Er3+ ions. For the understanding of such a catalytic process the charge transport in these systems is studied by an appropriate Monte Carlo simulation which includes phonons, charged impurities and traps. The obtained results evidence the important role of the traps for the transit of the electrons in the systems investigated here. They decrease the diffusion coefficient by about three orders of magnitude with respect to the bulk, from which it is possible to obtain a simple estimate of the reaction rate in agreement with experimental results. All the lanthanide-doped samples show a strong luminescence in the visible region. The emission bands are affected by a notable inhomogeneous broadening, indicating a high disorder of the crystalline environment of the lanthanide ions in the titania host.