Correlated structural-optical study of single nanocrystals in a gap-bar antenna: effects of plasmonics on excitonic recombination pathways

Abstract

We performed time-correlated single-photon counting experiments on individual silica coated CdSe/CdS core/thick-shell nanocrystal quantum dots (a.k.a., giant NQDs [g-NQDs]), placed on the plasmonic gap-bar antennas. Optical properties were directly correlated with the scanning electron microscopy (SEM) images of g-NQD-plasmonic antenna coupled structures. The structures, in which the g-NQDs are located in the gap of the antenna, afford a coupling with up to 9.6 fold enhancement of radiative recombination rates. These coupled g-NQDs are also characterized by a strong enhancement of bi-exciton emission efficiency that increases with their radiative enhancement factor. By analysing these findings with a simple model, we show that the plasmonic field of the antenna does not alter the Auger recombination processes of the bi-exciton states. As a result, enhancements of the single and bi-exciton radiative recombination rates lead directly to bi-exciton emission enhancement. These findings suggest that a plasmonic field can be utilized effectively in achieving a strong bi-exciton emission that is needed for photon pair generation and plasmon-assisted lasing.