Surface-related emissions and ferromagnetism in undoped ZnO nanorods

Pristine ZnO nanorods were synthesized by hydrothermal method. The samples have a single phase nature with wurtzite structure and no other impurity phases were detected. The presence of OH groups on the as-grown samples surface was confirmed. After vacuum annealing and H2O2 solution treatment, the surface states and oxygen vacancies were modified in ZnO nanorods, resulting in suppressing the visible emission band and reducing the room temperature ferromagnetism (RTFM). Experimental results suggest that OH groups could be responsible for the strong broad yellow emission band and RTFM for as-grown ZnO nanorods. Green emission bands in vacuum annealed and H2O2-solution-treated samples could be attributed to singly ionized oxygen vacancy (V0+). A plausible explanation for the observed weak RTFM is presented in terms of V0+ for the annealed sample, whereas V0+ and residual OH groups for H2O2-solution-treated samples.