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

Abstract

The formation of surface point defects in the initial stage of TiO₂ reduction (x ≤ 10¹² 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 TiO₂ 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 TiO₂ 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 TiO₂ sensitization in the visible spectral range.