Optical band-edge shift of anatase Ti1-xCoxO2-δ -: art. no. 193205

We report on the optical properties of magnetic cobalt-doped anatase phase titanium dioxide Ti1-xCoxO2-delta films for low doping concentrations, 0less than or equal toxless than or equal to0.02, in the spectral range 0.2less than or equal tohomega<5 eV. For well oxygenated films (delta<1) the optical conductivity is characterized by an absence of optical absorption below an onset of interband transitions at 3.6 eV and a blueshift of the optical band edge with increasing Co concentration. The absence of below band gap absorption is inconsistent with theoretical models which contain midgap magnetic impurity bands and suggests that strong on-site Coulomb interactions shift the O band to Co-level optical transitions to energies above the gap.