The secondary oxide phases in ZnO:Cr films have been observed to evolve from an initial Cr(2)O(3) phase near the film surface to a final ZnCr(2)O(4) phase throughout the film as the Cr content is increased. Two absorption bands, corresponding to the (4)A(2)->(4) T(1) and (4)A(2)->(4) T(2) transitions of Cr(3+), can be observed in the Cr(2)O(3)-rich sample, whereas the ZnCr(2)O(4)-rich sample is opaque at wavelengths <= 500 nm. Our results suggest that the formation of secondary oxide phases in ZnO:Cr films is inevitable, leading to a much lower solubility of Cr. (C) 2009 Elsevier B.V. All rights reserved.