Photon antibunching in enhanced photoluminescence of a single CdSe/ZnS nanocrystal by silver nanostructures

The photon antibunching behavior in the photoluminescence (PL) of single CdSe/ZnS semiconductor nanocrystals (NCs) interacting with the localized surface plasmon resonance (LSPR) of Ag nanostructure was investigated using fs-pulsed laser excitation at two excitation wavelengths. The time traces of the PL intensity, the PL decay curves, and the photon correlations of single NCs on a rough Ag film and on a coverslip were measured simultaneously, and an increase in the PL intensity accompanied by shortening of the PL lifetime was observed for the single NCs on the rough Ag film. The enhancement factor of the PL intensity depended on the excitation wavelength. Nearly all of the single NCs with enhanced PL exhibited photon antibunching behavior independent of the enhancement factor. Based on the enhanced radiative- and nonradiative-decay rates estimated from the experimental data, the mechanism of the photon antibunching behavior was considered as follows. To exhibit the photon antibunching behavior, the nonradiative Auger recombination between the generated excitons in a single NC is important. When the radiative- and the nonradiative-decay rates enhanced by the LSPR are faster than the Auger recombination rate, the probability of photon antibunching decreases. However, such fast radiative- and the nonradiative decay rates were not observed for single NCs interacting with the LSPR of the rough Ag film in this work. Therefore, the PL intensity from a single NC can be increased while maintaining the photon antibunching behavior. Our findings assist in the creation of effective single-photon sources and provide important information on the emission properties of an NC coupled with the plasmon of a metal nanostructure.