TEMPERATURE-PROGRAMMED DESORPTION AND PHOTO-LUMINESCENCE STUDIES OF THORIUM-DIOXIDE SURFACE-STATES

An apparatus was built which allowed us to prepare thoria surfaces in a high vacuum (≈10-8 Torr), to treat them in the presence of various gases, to analyze the gases desorbed at increasing temperatures, and to record photoluminescence spectra in various ambient conditions. Attention has been focused on the species responsible for the observed bands in the excitation and emission spectra. It is supposed that two of them are constituted by anionic vacancies, in the bulk and at the surface, and the third by surface OH groups. This ascription is confirmed by doping thoria with uranium, and allows us to propose a surface model consistent not only with the presently reported investigations, but also with the previously reported catalytic properties of thoria. © 1979.