The Origins of Photoluminescence Peaks in ZnO Nanocrystals Revealed by Microscopic Photoluminescence Imaging Spectroscopy

We report on the origins of photoluminescence (PL) peaks in ZnO nanocrystals (NCs) dispersed in glass films as determined using microscopic PL imaging spectroscopy. In macroscopic PL spectra, three main peaks were observed at low temperatures. When NC density in the films was decreased, two of the peaks were diminished, leaving only one dominant PL peak. Furthermore, only this PL peak was observed for isolated single NCs in the microscopic space-resolved PL spectra. The observed PL peaks were attributed to two origins: the intrinsic electronic state in isolated individual NCs, and the localized electronic states at the interface between aggregated NCs.