This paper describes methods for synthesizing different nanostructures of ZnO in aqueous solutions at low temperatures and examines the effect of the size of the synthesized samples on the photoluminescence (PL) spectra. As the diameters of the nanostructures increased, a decrease in the ratio of the intensity of the ultraviolet radiation band to the intensity of the yellow radiation band in the PL spectrum observed. It is found that changing the diameters of nanostructures from 15 nm to 1000 nm leads to a decrease in their bandgap energy (Eg) from 3.28 to 3.21 eV. When the diameters of the nanostructures were less than ~400 nm, it was found that the energy of the band gap was strongly depend on the size of the nanostructure, and that the bond was weaker as the size of the nanostructures exceeded 400 nm.
