Photoluminescence spectrum of highly excited single CdS nanocrystals studied by a scanning near-field optical microscope

Many-body effects in strongly photoexcited single CdS nanocrystals embedded in Al2O3 matrices have been studied by a scanning near-field optical microscope at low temperatures. Under weak excitations, we find a sharp photoluminescence (PL) band originating from the exciton recombination. With an increase of the excitation laser energy, the PL intensity increases and the broad PL band is superimposed on the exciton-related sharp PL band. From a theoretical analysis, it was concluded that the broadening of the PL band is due to electron-hole pairs in CdS nanocrystals. The many-body effects of correlated exciton systems in CdS nanocrystals will be discussed.