Point defects as the centers of titanium dioxide sensitization in the visible spectral range

The formation of surface point defects in the initial stage of TiO 2 reduction ( x ≤ 10 12 cm −2 ) has been studied by mass spectrometry and ultraviolet photoelectron spectroscopy (UPS). Heating to 720 K or UV illumination in ultrahigh vacuum creates surface color centers in TiO 2 with an energy spectrum extending from the Fermi level to the valence band top. The continuous photoelectron spectrum exhibits a peak at 2.7 eV, which varies in a manner correlated with the behavior of the optical absorption bands at 2.55 and 2.81 eV assigned to oxygen vacancies in the TiO 2 crystal structure. The interaction of the surface point defects with molecular oxygen has been studied and a special form of the photoadsorbed oxygen (with E des = 1.37 eV) is found. It is shown that the surface color centers may serve as centers of TiO 2 sensitization in the visible spectral range.