Light-induced spectral change and its restore process in the dark of nanocrystalline Y2O3:Tb were studied. It was observed that the intensity in 4f5d band increased by ultraviolet and visible irradiation. The smaller the particle size and the shorter the wavelength is, the larger the light-induced luminescent enhancement is. Two restore components were observed, corresponding to two defects, the internal and the surface. The studies on electron spin resonance (ESR) spectra indicate that optical irradiation eliminated the dangling Y-O bonds in the surface. (C) 2003 Elsevier B.V. All rights reserved.