Electronic state of nitrogen in doped titanium dioxide

Abstract

A yellow N-doped TiO2 powder was prepared by the sol-gel method using titanium tetra-isopropoxide and hydrazine monohydrate. An EPR signal was induced by the irradiation of light with hv ≥ 2.2 eV to the yellow TiO2 powder and the signal intensity gradually decreased in the dark. The EPR signal was due to thermally trapped carriers interacting with the doped N. The thermal activation energy of the trapped carriers was estimated to be 0.22 eV. XPS measurement was performed on the yellow powder as well as colorless and blue N-doped powders obtained by oxidation and reduction, respectively. The N1s bands at 399.5 eV can be assigned to nitrogen adsorbed on the surface. The atomic valence of nitrogen in the colorless, yellow and blue powders was positive, neutral and negative, respectively. The atomic valence of nitrogen in doped TiO2 depends on the oxidation-reduction procedure.