Temperature-dependent optical studies of Ti1−xCoxO2

We present the results of Raman and photoluminescence studies on epitaxial anatase phase Ti1−xCoxO2 films for x=0–0.07, grown by pulsed-laser deposition. The low-doped system (x=0.01 and 0.02) shows a Curie temperature of 700 K in the as-grown state. The Raman spectra from the doped and undoped films confirm their anatase phase. The photoluminescence spectrum is characterized by a broad emission from self-trapped excitons (STE) at 2.3 eV at temperatures below 120 K. This peak is characteristic of the anatase-phase TiO2 and shows a small blueshift with increasing doping concentration. The Co-doped samples show two spin-flip emission lines at 2.77 and 2.94 eV.