ZnO being a well known optoelectronic semiconductor, investigations related to the defects are very promising. In this report, we have attempted to detect the defects in ZnO nanoparticles synthesized by the conventional coprecipitation route using various spectroscopic techniques. The broad emission peak observed in photoluminescence spectrum and the non zero slope in Williamson-Hall analysis indicate the defects induced strain in the ZnO lattice. A few additional modes observed in Raman spectrum could be due to the breakdown of the translation symmetry of the lattice caused by defects and/or impurities. The presence of impurities can be ruled out as XRD pattern shows pure wurtzite structure. The presence of the vibrational band related to the Zn vacancies (V-Zn), unintentional hydrogen dopants and their complex defects confirm the defects in ZnO lattice. Positron life time components T-1 and T-2 additionally support V-Zn attached to hydrogen and to a cluster of Zn and O di-vacancies respectively. (C) 2012 Elsevier Ltd. All rights reserved.