Auger electron spectroscopy (AES), cathodoluminescence (CL) spectroscopy, and x-ray photoelectron spectroscopy (XPS) were used to study the CL intensity degradation Of SiO2: Cb, Tb powder phosphors prepared by a sol-gel process. The AES and the CL data were collected simultaneously when the powders were bombarded for 10 h with a beam of electrons of current density of 54 mA/cm(2) accelerated by 2 kV in a vacuum chamber containing either 1 X 10(-8) or 1 X 10(-7) Torr O-2. A decrease of CL intensity was simultaneous with desorption of oxygen (O) from the surface, i.e., there is a correlation between the degradation of CL intensity and desorption of O. The AES and the XPS data suggest that a nonluminescent oxygen-deficient layer of SiOx (x < 2) that could decrease the CL intensity was formed on the surface. Mechanisms by which oxygen desorption leads to a reduction of the CL intensity are discussed. (c) 2007 American Vacuum Society.