Pulsed laser deposition has been used to prepare thin films of ZnO on (0 0 0 1) sapphire at 400 degreesC. The target-substrate distance and the background oxygen pressure were varied. A time-of-flight ion probe was used to investigate the interaction of the laser ablation plume with the background gas and measure the ion flux at the substrate. The film properties were measured using X-ray diffraction and photoluminescence spectroscopy. It has been shown that crystalline quality and the photoluminescence properties are better at higher oxygen pressures, which give a longer plasma residence time at the substrate. (C) 2002 Elsevier Science B.V. All rights reserved.