The preparation and characterization (structural, morphological, and optical) of ZnO nanoparticles were studied for different reaction conditions (stirring velocities, temperatures, concentrations of reactants and capping). The wet chemistry route was used to produce the nanosized particles. X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and fluorescence spectroscopy techniques were used for characterization. ZnO nanoparticles in the size range from 5 to 15 nm were measured by TEM and XRD measurements. We find that the average size of the nanoparticles changes with temperature, stirring velocity, capping and concentration of reactant. As temperature, stirring velocity and reactant concentration are increased the average size of the particles increase and capping the particle prevents/reduces larger nanoparticles. Additionally, all possible transitions coming/resulting from both band-edge and deep-traps were determined by using fluorescence measurements. We showed that the wavelength of the emitted light observed around 380 nm, 423 nm, 450 nm, 463 nm, and 485 nm result from band-edge emissions whereas emission peaks between around 490 nm and 559 nm result from deep-trap transitions. (c) 2012 Elsevier B.V. All rights reserved.