A novel, simple and effective surface passivation technique is introduced to enhance UV spectrum selectivity of ZnO nanoparticles (NPs). The technique which exploits an absorbed layer of dimethylformamide, enables the synthesis and surface passivation of ZnO NPs through a single-step process. Pure ZnO NPs and passivated ones were characterized to evaluate the integrity of passivating layer as well as quality of the final product. Morphological examinations were performed using field-emission scanning and transmission electron microscopies. X-ray diffractometry, energy dispersive X-ray and fourier-transform infrared spectroscopies were employed to analyze the phase and chemical composition of the samples. We also compared optical properties of the surface-passivated and pure ZnO NPs. Photoluminescence measurements revealed a peak value for UV emission at 394 nm and one for violet emission at 412 nm for the passivated and pure samples; respectively. A significant enhancement was observed in the spectrum selectivity and absorption efficiency of the passivated ZnO NPs in the UV range. The passivated NPs exhibited high UV-to-visible rejection ratio and UV-blocking capacity which provide a promising candidate for visible-blind UV photodetectors and UV shielding applications.