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.

Quantum Optical Signature of Plasmonically Coupled Nanocrystal Quantum Dots

“…The fits to two single g‐NQDs that are coupled to the antennas (Figure b blue points and Figure S6a, Supporting Information) also give A values of 8.6 and 9.5, respectively, indicating that coupling to the antennas does not provide any enhancement to σ at the laser excitation wavelength of 405 nm. This finding is consistent with the results of our simulated and experimentally measured light scattering spectra, both of which show no enhancement at 405 nm …”

“…The dimensions are selected to achieve a plasmon resonance that overlaps directly on PL emission band of the QDs (640 nm). This overlap, confirmed by the measured scattering spectra, ensures strong enhancement to the dipole–dipole interaction. While any antenna in resonances with the emission of QDs can in principle be utilized, we chose this geometry to make placement of nanocrystal quantum dots (NQDs) easier.…”

Coupling Single Giant Nanocrystal Quantum Dots to the Fundamental Mode of Patch Nanoantennas through Fringe Field

“…PL intensity-time traces, PL decay curves, and 2 nd order photon correlation functions providing a measure on relative emission efficiency of bi-exciton emission process 24 25 26 27 are compared with those of referenced g-NQDs spread on the glass substrates. They are also compared with those measured on g-NQDs placed in the center of parallel gap-bar antennas utilizing two-step e-beam lithography (see Supporting Information S2 ) 17 24 . The gap-bar antennas are also designed to be in resonance with the emission band of the g-NQDs.…”

“…All these applications, however, necessitate the ability to precisely position or align the quantum emitters with respect to the antennas so that strong coupling between them can be induced. In the past few years, several bottom-up self-assembly approaches 15 16 as well as top-down electron beam lithography-based approaches 11 17 have been developed to realize the desired alignments. Notably, single nanocrystal quantum dots (NQDs) have been incorporated into 14–30 nm gaps of dimer nanoantennas by using a two-step e-beam lithography method 11 .…”

Effect of Spectral Overlap and Separation Distance on Exciton and Biexciton Quantum Yields and Radiative and Nonradiative Recombination Rates in Quantum Dots Near Plasmon Nanoparticles

“…For example, it was shown that when QDs were attached to the plasmonic gap-bar antennas, the EX radiative recombination rate increased, but this process did not affect the BX QY. [37] Thus, the effects of PNPs on BX PL are ambiguous. On the one hand, the EX QY can be reduced by metal-induced quenching; on the other hand, BX QY can be enhanced by the Purcell effect, and at the same time, plasmon-induced local electromagnetic field can affect the photon statistics of higher-order excitonic quasiparticles.…”