The surface state of Y-3(Al,Ga)(5)O-12:Tb phosphor was determined before and after 27 h of prolonged electron beam exposure. The electron irradiation was carried out at a base pressure of 2.3 x 10(-8) Torr and an oxygen pressure of 1.0 x 10(-6) Torr. New surface layers were formed after the chemisorbed species were removed as a result of electron stimulated surface chemical reactions. The rate of the removal of the chemisorbed species from the phosphor's surface during prolonged electron irradiation was affected by the background working atmosphere as measured with Auger electron spectroscopy combined with cathodoluminescence (CL) spectroscopy. The CL intensity of the Y-3(Al,Ga)(5)O-12: Tb stabilized after removal of the chemisorbed species and stayed constant during further electron irradiation, indicating that this phosphor is good for the technology used in field emission displays. There was an increase in the Al, Y, O and Tb Auger peak intensities pointing to the formation of a complicated surface structure that was probably a combination of more than one chemical compound. X-ray photoelectron spectroscopy results suggested electron-beam induced formation of new interleave oxide layers, such as AlOx, YOx and Y(Al,Ga)O-3 on the surface. These oxide layers acted as a protective layer inhibiting further CL intensity degradation during prolonged electron irradiation. (C) 2012 Elsevier B.V. All rights reserved.