Influence of precursor age on defect states in ZnO nanorods

The aim of the work is to clarify the influence of the precursor age and post-deposition treatment on defect states of hexagonally shaped ZnO nanorods grown by hydrothermal process. Photoluminescence, radioluminescence and thermally stimulated luminescence indicate that ZnO nanorods synthetized from aged precursors possess larger amount of defects and charge traps. Electron paramagnetic resonance (EPR) shows the dominant signal with the 1.96 g-factor together with subsidiary resonances probably coming from precursor salt residuals used during the sample growth. All samples exhibit a change of the 1.96 g-factor signal intensity after X-ray irradiation. Stepwise annealing in air at elevated temperature removes the subsidiary resonances and corresponding defects. A new EPR signal with the 2.0038 g-factor appears after the X-ray irradiation, air annealing and plasma hydrogenation. It was attributed to surface defects.