ZnO thin films synthesized using a sol-gel method were found to have a high density of nanocrystals embedded in an amorphous matrix despite the process performed at a low temperature. Photoluminescence (PL) of nanocrystal-embedded as-grown ZnO films consisted of ultraviolet emissions related to a quantum confinement effect in the nanocrystals, the amorphous phase in the matrix, and bulky ZnO film. In contrast, thermal annealing resulted in a blue-shifted emission at 3.390 eV from the fine nanocrystals and an intense emission at 3.339 eV from the coarse nanocrystals. The quantum confinement effect in nanocrystals was confirmed by the estimated blue-shift according to the nanocrystal size and a comparison of the PL peak positions. (C) 2009 Elsevier B.V. All rights reserved.