Optical emission properties of nanocrystalline TiO2 powder and of polycrystalline TiO2 obtained by powder sintering have been studied by cathodoluminescence in the scanning electron microscope. Radiative transitions in nanocrystalline TiO2 powder were associated with shallow traps induced by surface oxygen vacancies. In polycrystalline TiO2 the presence of shallow traps diminishes and the radiative transitions involve energy levels induced by Ti3+ ions. A red shift of the infrared emission band of titanium ions appears to he determined by oxygen vacancies affecting the band gap energy. (C) 2008 Elsevier B.V. All rights reserved.