ZnO is synthesized by low temperature solution precipitation technique using polyvinyl pyrrolidone (PVP) as capping agent and at varying pH of the precipitating solution. The as-synthesized ZnO has a cone shape with rough surface, due to the chemisorption of PVP. The results show that PVP has a significant role in the nucleation and growth of ZnO at low temperature and a pH of 11 is required for the formation of the ZnO phase. When it is calcined at 550 degrees C, the morphology is modified to smooth nanocones. As the ZnO is calcined, optical bandgap is decreased and altered the nonlinear absorption properties of nano ZnO. The optical limiting property of ZnO colloids is investigated using Z-scan technique. Enhanced optical limiting is observed for ZnO calcined at 550 degrees C. (C) 2013 Elsevier Ltd. All rights reserved.