Correlation among oxygen vacancy and doping concentration in controlling the properties of cobalt doped ZnO nanoparticles

We have observed ferromagnetism at room temperature in 2% cobalt doped ZnO nanoparticles prepared by a simple chemical precipitation method. This can be described as a consequence of bound magnetic polaron (BMP) resulting from the occurrence of oxygen vacancies and surface defects in the sample. Photoluminescence and Raman measurements indicate the existence of such defects in the sample. Electron Spin Resonance (ESR) studies are done to probe into the magnetic nature of the doped samples further. Redshift in the band gap and formation of characteristic absorption bands after Co doping shows that Co ions are incorporated in the host ZnO lattice. The infrared sensitive vibrational modes are identified with Fourier Transform Infrared Spectroscopy (FTIR) measurements. The spin-orbital splitting in X- ray Photoelectron Spectroscopic (XPS) measurements show the matching oxidation (divalent) state among the dopant and the host. Local structural studies after Co doping by the Extended X-ray Absorption Fine Structure (EXAFS), shows the Co2+ integration in the ZnO lattice without any impurity states. Photocatalytic measurements show that ZnO is a very promising degrading agent for Rhodamine B dye solution under UV as well as solar irradiation.