Un-doped Al (0-9 at.%) nanoparticles and doped ZnO powders were prepared by the sol-gel method. The nanoparticles were heated at 700-800 degrees C for 1 h in air and then analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectra and photoluminescence (PL). The results of undoped (ZnO) and Al-doped ZnO (AZO) nanoparticles were also compared to investigate the structural characteristics and physical properties. XRD patterns of AZO powders were similar to those of ZnO powders, indicating that micro-Al ions were substituted for Zn atoms and there were no variations in the structure of the ZnO nanoparticles. From the XRD and SEM data, the grain size of the AZO nanoparticles increased from 34.41 to 40.14 nm when the annealing temperature was increased. The Raman intensity of the AZO nanoparticles (Al = 5 at.%) increased when the annealing temperature was increased. Increasing the degree of crystalline not only reduced the residual stress, but also improved the physical properties of the nanoparticles. (c) 2008 Elsevier B.V. All rights reserved.