Zn1-xCoxO films prepared with different molar ratio of cobalt acetate to zinc acetate were deposited on substrates by the sol-gel technique. X-ray photoelectron spectroscopy, X-ray diffraction, photoluminescence and ferromagnetism measurements were used to characterize the Zn1-xCoxO diluted magnetic semiconductors. The authors found that the magnetic properties of the films arise from the replacement of Zn by Co in the ZnO lattice and zinc vacancies were determined in the photoluminescence band. Therefore, an increase in cobalt concentration and the number of zinc vacancies in the oxygen-rich Zn1-xCoxO film may lead to the enhancement of the magnetic properties. It is worth noting that changes in cobalt concentration and the number of zinc vacancies are important issues for producing strong ferromagnetic Zn1-xCoxO films prepared by the sol-gel method. (c) 2008 Elsevier B.V. All rights reserved.