Pulsed laser deposition has been successfully used to achieve in-situ nitrogen doping of zinc oxide thin films at a temperature as low as 300 degrees C. Nitrogen-doped zinc oxide (ZnO:N) thin films with a maximum nitrogen content of 0.7 at.% were obtained by varying the nitrogen background pressure in the range of 0-150 mTorr. The ZnO:N thin films were found to present hexagonal crystalline structure with dense and smooth surface. X-ray photoelectron spectroscopy analysis confirms the effective incorporation of nitrogen into ZnO thin films. Optical transmission together with room temperature photoluminescence measurements show that the band gap of the ZnO:N films shifts from 3.3 eV to 3.1 eV as nitrogen concentration varies in the range of 0.2-0.7 at.%. The narrower band gap is obtained at an optimal nitrogen concentration of 0.22 at.%. This band gap narrowing is found to be caused by both nitrogen incorporation and nitrogen-induced defects in the ZnO:N films. (C) 2014 Elsevier Ltd. All rights reserved.