Induced ferromagnetic and gas sensing properties in ZnO-nanostructures by altering defect concentration of oxygen and zinc vacancies

We report on the effect of the synthesis reaction-time on the structural, optical, magnetic and sensing properties of ZnO-nanostructures. Electron paramagnetic resonance and photoluminescence analyses reveal that singly ionized oxygen vacancies (VO+) and zinc vacancies (V_Zn) are the main defects and that their relative concentration decreases with increasing particle sizes, resulting in decreased ferromagnetism (FM). Moreover, the sensing performance decreased with an increase in nanostructures synthesis reaction-time due to a decreased surface area, as well as VO+ and V_Zn concentrations. Thus, the synthesis reaction-time clearly controls the relative occupancy of the VO+ and V_Zn present on the surface of ZnO-nanostructures, which is enunciated to be critical for enhanced FM and sensing characteristics.