ZnO thin films were deposited on (0001) Al2O3 substrates depending on oxygen partial pressure by pulsed laser deposition. Optical properties of ZnO were investigated by photoluminescence (PL). The relationship between PL and electron concentration has been investigated. Origin of the dominant ultraviolet (UV) emission in ZnO thin film measured at room temperature was identified as a free electron-neutral-acceptor transition (eA(0)) through temperature dependence of PL measurement. The UV emission intensity at room temperature is related to variation of electron concentration because a free-electron-neutral-acceptor transition (eA(0)) as origin of UV emission at room temperature is related to impurity concentration of ZnO. (c) 2007 Elsevier B.V. All rights reserved.