Co2+-doped Y3Al5O12 (Co2+:YAG) nanocrystalline powder sample was obtained by sol-gel method. The gel with the composition Of CoO-Y2O3-Al2O3 was prepared from nitrates of yttrium, aluminum, cobalt and citric acid, and was heat-treated at temperatures ranging from 400 to 1000degreesC. The heated powder samples at different temperatures were characterized by X-ray diffraction analysis (XRD), transmission electron microscope (TEM), infrared spectra (IR) and emission spectra. Results showed that when the gel was heat-treated at 800degreesC, YAG nanocrystals with sizes 30-70 nm were formed. The emission spectrum of the heat-treated powders is identical to that of tetrahedral Co2+ ions, which shows that Co2+ ions are embedded in the lattice sites of YAG nanocrystals and are coordinated with four oxygens. (C) 2003 Elsevier B.V. All rights reserved.