Correlation Between Optoelectronic and Positron Lifetime Properties in As‐received and Plasma‐treated ZnO Nanopowders

We employed photoluminescence and positron lifetime measurements on a number of commercially available ZnO nanopowders. The experiments were performed before and after processing of these samples in remote N and O/He plasma. In all the nanopowders, the average lifetime component is substantially longer than in a single‐crystalline sample, consistent with the model of grains with defect‐rich surface and subsurface layers. However, the sample‐to‐sample differences in the quality of the powders, as detected by the photoluminescence spectroscopy, obscure observation of possible size effects. Compression of the powders into pellets yields reductions of the average positron lifetimes. Plasma‐induced modifications are most visible in the low‐temperature photoluminescence spectra of the smallest nanocrystals, indicative of a surface‐specific nature of the chosen treatment procedure.