Octylamine capped ZnO nanoparticles with mean diameters in the range of 4-14 nm were obtained by thermolysis of single source metal-organic precursors. The nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, and UV-visible, luminescence, and excitation spectroscopies. The nanocrystals are sufficiently defect-free to exhibit band edge luminescence. The size dependence of the changes in the band gap have been calculated by different methods and compared with the Kayanuma model.