Correlation between oxygen vacancies and dopant concentration in Mn-doped ZnO nanoparticles synthesized by co-precipitation technique

Zn1-xMnxO nanoparticles with different Mn concentration (0.01-0.1) were synthesized by co-precipitation technique. The structural, optical and magnetic properties of Zn1-xMnxO nanoparticles were investigated. The Zn1-xMnxO nanoparticles keep wurtzite structure without any impurity phase until the Mn concentration reaches 0.1. The magnetic measurements show ferromagnetism of Zn1-xMnxO nanoparticles is improved with increase of the Mn concentration (x = 0.01-0.08). The optimal doping concentrations for enhancement in ferromagnetism of Zn1-xMnxO nanoparticles is 0.08. The reduction in ferromagnetism of Zn0.9Mn0.1O is caused by coexistence of the Mn3+ and Mn2+ ions, which can form antiferromagnetic interaction. Results of UV-vis absorption spectra indicate that the bandgap and carrier concentration increase gradually with increasing Mn concentration, which can be explained by Burstein-Moss shift. Singly charged oxygen vacancies in the Zn1-xMnxO were analyzed according to the visible photoluminescence spectra results. Experiment results reveal that the singly charged oxygen vacancies and surrounding Mn2+ ions form bound magnetic polarons model, which is responsible for the origin of ferromagnetism in Mn-doped ZnO nanoparticles.