Defects present in ZnO nanocrystals prepared by a wet chemical method were characterized by photoluminescence and positron annihilation spectroscopy (PAS) techniques. The as-prepared sample was heat treated at different temperatures to obtain nanocrystals in the size range of 19–39nm. X ray diffractograms confirmed the single-phase wurtzite structure formation. Photoluminescence measurements showed a strong violet band at 434nm, which was identified as due to electronic transitions from the Zn interstitial defect level to the top of the valence band. A marked decrease in the intensity of the violet emission with increasing heat-treatment temperature was observed, which was attributed to recombination of Zn interstitials with Zn vacancies. Positron annihilation spectroscopy was employed to understand the dynamics of the vacancy-type defects and their annealing behavior. The observed variation of the defect related lifetime components with heat-treatment temperature was successfully explained by using a three-state trapping model. The results of photoluminescence and PAS studies in the present case were found to be complementary to each other.

Characterization of Defects in ZnO Nanocrystals - Photoluminescence and Positron Annihilation Spectroscopic Studies. A.K.Mishra, S.K.Chaudhuri, S.Mukherjee, A.Priyam, A.Saha, D.Das: Journal of Applied Physics, 2007, 102[10], 103514