Zn1-xCoxO (0 <= x <= 0.2) nanoparticles were prepared by co-precipitation method followed by drying at 200 degrees C and subsequent annealing at 500 degrees C. A non-ionic surfactant, Tween-80 which was not reported in earlier studies, was used during the preparation process. X-ray diffraction analysis showed the formation of wurtzite ZnO phase nanostructures. The Rietveld analysis showed the appearance of impurity phase (Co3O4), which was notably present at higher Co doping concentration (x = 0.2). Morphological observations using scanning electron microscopy show the formation of nanoparticles with remarkable morphologies. Photoluminescence spectra revealed emission bands in both UV and visible regions due to the defect centers acting as trap levels. Optical studies carried out by diffuse reflectance spectroscopy (DRS) indicated a decrease in the value of the band gap with increasing Co doping concentration. The elemental composition of Zn, Co and O was quantitatively obtained from EDAX analysis which confirmed the purity of the as-prepared nanopowders and that the chemical composition is close to the starting stoichiometries. Magnetisation-Field (M-H) hysteresis curves revealed the appearance of ferromagnetic behaviour, where the magnetic characteristics such as coercivity and saturation magnetization values, were found to be sensitive to Co doping level. (C) 2015 Elsevier B.V. All rights reserved.