Photocatalytic properties of TiO2 are expected to play an important role on emerging technologies based on OH radicals to destroy harmful nonbiodegradable organic and inorganic contaminants in water. The drawback is the wide band gap of TiO2 (3.2eV) limiting its use to the UV part of electromagnetic spectrum under sunlight. Therefore, modifications of TiO2 are needed to tune the gap in order to allow an efficient use of the entire solar spectrum. One possibility is N-doping of TiO2 to make the photocatalytic activity possible under visible light and more suitable for water treatment.In our study nitrogen-doped TiO2 (TiO2−xNx) films were deposited by DC-reactive magnetron sputtering using a dual-magnetron co-deposition apparatus on unheated glass and silicon substrates using a pure titanium target. The depth profile of nitrogen was measured with heavy ion elastic recoil detection analysis combined with Rutherford backscattering spectrometry (RBS) and correlated with the optical and structural properties obtained by UV–VIS spectroscopy and X-ray diffraction (XRD).