Optical absorption of polydisperse TiO2: Effect of surface doping by transition metal cations

We have investigated the effect of doping of nanocrystalline TiO2 with transition metal cations (Cu2+, Fe3+, Co2+ and Cr3+) on the properties related to optical absorption. The metal-doped TiO2 samples obtained by us have been characterised using an X-ray diffractometry, X-ray fluorescence analysis, a scanning electron microscopy, and a UV-visible absorption spectroscopy. It has been shown that the doping effects on the properties of anatase and rutile are quite different, being much stronger and complicated in the case of anatase. The anatase doped with Fe and Cr cations reveals a 'red' shift of the absorption edge and narrowing of the bandgap.