The nitrogen photoactive centre in N-doped titanium dioxide formed via interaction of N atoms with the solid. Nature and energy level of the species

N-doped titanium dioxide has been prepared generating a nitrogen plasma in the atmosphere over a sample of pre-reduced TiO2. This solid, investigated by EPR and XPS, is similar to materials prepared via sol-gel or different chemical methods. The cleaner preparation method, however, avoids complications in the assignments due to by-products of the chemical synthesis. The experiment unambiguously confirms previous theoretical forecast and indicates the formation of an interstitial paramagnetic nitrogen species already described in the case of sol-gel prepared materials. The energy of this species lies slightly over the valence band limit and well below the Ti3+ states of reduced TiO2.