By a modified sol-gel method, from ethanolic solutions, Zn1-xCoxO nanoparticles have_x000D_ been synthesized. The effect of cobalt content in the crystal structure, wide band gap,_x000D_ and luminescence of ZnO nanoparticles have been observed. The immediate qualitative_x000D_ effect was the greenish hue of the final product obtained, which was more intense as_x000D_ cobalt percentage increased. The optical absorbance analysis by UV-vis spectroscopy_x000D_ showed three characteristic bands assigned to cobalt ion, which indicates the effective_x000D_ incorporation of ion dopants in the crystal structure of the ZnO host. The excitonic_x000D_ nature of the nanoparticles was clearly detected. However, in general, a redshift of the_x000D_ energy band gap as the cobalt content increasing was observed. By Photoluminescence_x000D_ spectroscopy, at room temperature, two emission bands were eviden...