title: Origin of photoactivity of nitrogen-doped titanium dioxide under visible light.
abstract: Nitrogen-doped titanium dioxide (N-TiO2), a photocatalytic material active in visible light, has been investigated by a combined experimental and theoretical approach. The material contains single-atom nitrogen impurities that form either diamagnetic (Nb-) or paramagnetic (Nb*) bulk centers. Both types of Nb centers give rise to localized states in the band gap of the oxide. The relative abundance of these species depends on the oxidation state of the solid, as, upon reduction, electron transfer from Ti3+ ions to Nb* results in the formation of Ti4+ and Nb-. EPR spectra measured under irradiation show that Nb centers are responsible for visible light absorption with promotion of electrons from the band gap localized states to the conduction band or to surface-adsorbed electron scavengers. These results provide a characterization of the electronic states associated with N impurities in TiO2 and, for the first time, a picture of the processes occurring in the solid under irradiation with visible light.
authors.affiliation: Dipartimento di Chimica IFM, Università di Torino and NIS Center of Excellence, Via P. Giuria 7, 10125 Torino, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Livraghi
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Paganini
authors.forename: Elio
authors.initials: E
authors.lastname: Giamello
authors.forename: Annabella
authors.initials: A
authors.lastname: Selloni
authors.forename: Cristiana
authors.initials: C
authors.lastname: Di Valentin
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Pacchioni