Colloidal ZnO nanoparticles have been studied extensively in the past three decades. Luminescense of these quantum dots is dominated by both excitonic and a broad visible emission associated with the anion/cation deficiencies of the lattice. In this work, we present synthesis and characterization of highly blue-emitting ZnO colloidal nanoparticles and their thin films supported by UV-visible, fluorescence, Raman, and FTIR spectroscopies as well as TEM and Powder XRD. A mechanism for the growth of the colloidal particles, in particular the role of temperature, is also presented.