Co2+-doped LiAl5O8 (Co2+ :LAO) nanocrystalline powder sample was obtained by sol-gel method. The gel with the composition of CoO-Li2O-Al2O3 was prepared from lithium acetate, nitrates of aluminum and cobalt, citric acid, and was heat-treated at temperatures from 500 to 1000 degrees C. The heated powder samples at different temperatures were characterized by differential thermal and thermogravimetric analysis (DTA/TG), X-ray diffraction analysis (XRD), transmission electron microscope (TEM), infrared spectra (IR) and absorption spectra. The results show that when the gel was heat-treated at 700 degrees C, LiAl5O8 nanocrystals with size of 20-40nm were formed. The absorption 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 LiAl5O8 nanocrystals and are coordinated with four oxygens. (c) 2005 Elsevier B.V. All rights reserved.