Influence of Co doping on the structural, optical and magnetic properties of ZnO nanocrystals

•Co doping on the structural, optical and magnetic properties of ZnO nanocrystal.•Generation of defects such as Oxygen vacancies and impurity.•Their presence due to the disorder of oxygen lattice.•Blue shift in absorption spectra with increasing Co, due to d–d interactions.•FM arise from the intrinsic exchange interaction of magnetic moments. A systematic investigation on the synthesis, characterization, optical and magnetic properties of Co doped ZnO nanocrystals have been reported. Nanocrystals of Zn1−xCoxO (where x=0.05 and 0.10) were synthesized using the Sol–gel technique. Structural, optical and magnetic properties of the samples were investigated by X-ray diffraction (XRD), UV–VIS–NIR spectroscopy, Raman spectroscopy and SQUID magnetometer. Energy dispersive X-ray, Scanning electron microscopic, XRD and Raman measurements showed that the Co ions were successfully doped at the Zn site in the wurtzite type ZnO lattice. An appreciable blue shift in the absorption spectrum was observed, which indicates that the Co doping in ZnO leads to systematic increase in the band-gap with dopant concentration. Magnetization studies showed that the Co doped ZnO nanocrystals display room temperature ferromagnetism and the ferromagnetic ordering strengthens with the Co concentration.