Synthesis of Co-doped ZnO nanoparticles via co-precipitation: Structural, optical and magnetic properties

• Decrease in band gap on doping ZnO with Co2 + fractions
• Confirmation of hexagonal wurtzite structure by Rietveld analysis
• Strong emission bands in the visible regions due to defects
• Decrease in magnetic moment with increase in Co2 +
• Magnetic ordering was disturbed by annealing.

Zn1-xCoxO (0 ≤ x ≤ 0.2) nanoparticles were prepared by co-precipitation method followed by drying at 200 °C and subsequent annealing at 500 °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.

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