Optical Properties of a Nanocrystalline Co-Doped TiO2 after Various Treatments

Abstract

The absorption spectra of cobalt-doped anatase TiO₂ nanopowders in the infrared and visible ranges have been studied after various oxidative and reductive treatments. The annealing leads to the appearance of the Drude-like contribution in the infrared region and significant change in the absorption in an visible range due to the formation of defects of the oxygen-vacancy-type and Ti³⁺ ions. The observed additional contribution in the absorption spectra of TiO₂:Co nanopowders as compared to the spectra of undoped powders is ascribed to the d–d transitions in ions Co²⁺. The change in the absorption related to cobalt after annealing is explained by a change in the local environment of Co ions from the octahedral to the tetrahedral environment.