Well-aligned ZnO nanorod arrays were prepared on Si substrates modified with ZnO seeds using a low temperature hydrothermal method. In particular, photoluminescence (PL) properties of the ZnO nanorods can be easily tuned by varying the treatment duration of O-2 plasma. Penetration depth of oxygen ions near the surface is suggested to influence the effect of O-2 plasma on modification of PL properties for ZnO nanorods with different sizes. O-2 plasma-tuned optical quality for ZnO nanorods has been attributed to the change of depletion region width. (C) 2013 Elsevier B.V. All rights reserved.