Photoluminescence (PL) of zinc oxide (ZnO) nanorods with an average thickness of 5 nm and a length of 30 nm is blue-shifted compared to the bulk due to quantum confinement effects. The exciton states remain relatively stable at a high carrier density due to a smaller exciton size and an enhanced exciton binding energy in the quantum confined nanorods, whereas the electron-hole plasma states are formed in the bulk at the similar carrier density. A linear dependence of the PL intensity on the excitation intensity also corroborates the assumption that the stable exciton states are responsible for the undisturbed emission at a high carrier density. (C) 2008 Elsevier B.V. All rights reserved.