Super-Poissonian Statistics of Photon Emission from Single CdSe-CdS Core-Shell Nanocrystals Coupled to Metal Nanostructures

We demonstrate that photon antibunching observed for individual nanocrystal quantum dots (NQDs) can be transformed into photon bunching characterized by super-Poissonian statistics when they are coupled to metal nanostructures (MNs). This observation indicates that, while the quantum yield of a biexciton (Q2X) is lower than that of a single exciton (Q1X) in freestanding NQDs, Q2X becomes greater than Q1X in NQDs coupled to MNs. This unique phenomenon is attributed to metal-induced quenching with a rate that scales more slowly with exciton multiplicity than the radiative decay rate and dominates over other nonradiative decay channels for both single excitons and biexcitons.