Well-aligned ZnO nanorod arrays with different average diameters were grown by hydrothermal method in the presence of Cu ions in the deposition solution. Cu ions significantly inhibit diameter growth of ZnO nanorods and influence the luminescence properties. Quantitative analyses reveal that Cu ions were not incorporated into the synthesized nanorods. Photoluminescence spectra show that a weak ultraviolet emission and a strongly broad visible emission band in yellow region under ultraviolet light excitation for as-grown ZnO nanorods. The intensity of yellow emission bands decreases with Cu ions concentration increasing and the peak position has a blue-shift after low temperature thermal treatment. Photoluminescence spectra under different excitation energies and photoluminescence excitation spectra reveal that the yellow emission bands and green (blue) emission bands are associated with zinc interstitial related shallow donor level and oxygen vacancies related deep donor level as initial states, respectively. A plausible growth mechanism has been proposed to explain the narrowed diameter for ZnO nanorods in the presence of Cu ions based on crystallographic habits of wurtzite hexagonal. (C) 2012 Elsevier B.V. All rights reserved.