Influence of cobalt doping on structure, optical and magnetic properties of spray pyrolysed nano structured ZnO films

Zn_1-xCo_xO (x = 0–10 at%) films were prepared using the spray pyrolysis method at 723 K on glass substrates. The structural and transport properties of Zn_1-xCo_xO deposits were studied using X-ray Diffraction(XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), UV-VIS Spectrophotometer and Vibrating Sample Magnetometer (VSM). XRD analysis confirmed a hexagonal wurtzite-type structure with a preferential orientation in the (0 0 2) plane, indicating Co²⁺ ion in the ZnO host matrix, and absence of secondary phase of the metals in the ZnO host matrix. The surface morphology modified from fibrous to spherical grain shape with enrichment of cobalt in the deposits. The composition analysis indicates the existence of Zinc and Cobalt. The XPS analysis provides the dopant exists in Co²⁺ state. The optical absorption edge shift to a higher wavelength of three band transitions corresponds to the ⁴A₂→² E(G), ⁴A₂→⁴T₁(P) and ⁴A₂→²A₁(G) states. The reduction of energy band gap Eg₁ in the UV region and Eg₂ in the visible region was observed, which is due to the spin exchange interaction occurs in the sp-d transition state. At room temperature photoluminescence (PL) spectra showed emission in the UV and entire visible region due to the various defect states present in the deposits. All deposits show paramagnetic behavior even at low temperature.