Tunable Plexcitonic Nanoparticles: A Model System for Studying Plasmon–Exciton Interaction from the Weak to the Ultrastrong Coupling Regime

Abstract

Controlling the number of dye molecules on metallic nanoparticles, which in turn affects the magnitude of Rabi splitting energy, is crucial for obtaining hybrid metal core−organic shell nanoparticles with tunable optical properties in the visible spectrum since the magnitude of the Rabi splitting energy directly determines the strength of the coupling between plasmonic nanoparticles and dye molecules. In this work, we present a new method for the synthesis of plexcitonic nanoparticles, and thus we are able to control the number of dye molecules self-assembled on Ag nanoprisms (Ag NPs) by adjusting the concentration of dye molecules used in the synthesis. Indeed, individual dye molecules self-assemble into J-aggregates on Ag NPs. Thus, in the finite-element simulations and experimental data of the hybrid metal organic nanoparticles, we observed a transition from weak coupling to the ultrastrong coupling regime. Besides, ultrafast energy transfer between plasmonic nanoparticles and excitonic aggregated dye molecules has been extensively studied as a function of Rabi splitting energy. We observe that the lifetime of the polariton states increases with the coupling strength and the upper polaritons are short-lived, whereas the lower polaritons are long-lived. Hybrid metal−organic nanoparticles presented in this study (i) have tunable Rabi splitting energies, (ii) are easy to prepare in large quantities in aqueous medium, (iii) can be uniformly assembled on solid substrates, (iv) have resonance frequencies in the visible spectrum, and (v) have small mode volume, thus making them an excellent model system for studying light−matter interaction at nanoscale dimensions from the weak to ultrastrong coupling regime.

What’s so Hot about Electrons in Metal Nanoparticles?

“…For example, there have only been a handful of dynamics measurements, and at present it is not clear how the lifetimes of the coupled states are related to the initial SPP/exciton states. 147,150,[170][171][172] Another interesting problem regarding the exciton-plasmon interaction is the exciton-plasmon coupling in the quantum regime of a single exciton, where the absorption line-shape can become Fano-like. [173][174][175] This quantum regime was only recently observed and reported in Ref.…”

Revealing Strong Plasmon-Exciton Coupling between Nanogap Resonators and Two-Dimensional Semiconductors at Ambient Conditions

“…To date, however, there remain a plenty of ambiguities in the development of plasmon-exciton coupling in TMDC MLs, mainly induced by unique excitonic properties in these crystalised ultrathin nanosheets. For example, it is unknown whether or not the exciton number N can be flexibly tuned, because excitons in TMDC MLs are quasiparticles formed in semiconductor bandgap, unlike in the case of dye molecule [23,24] and rare-earth ion [25][26][27] systems, where N can be adjusted by changing the doping concentration; and it is uncertain whether or not the large exciton coherence size hinders further enhancement of coupling strength, since it is believed that EM dipoles must have larger dimensions than exciton coherence size to enable the coupling [21], which con-FIG. 1.…”

Strong Coupling in Microcavity Structures: Principle, Design, and Practical Application

“…As mentioned earlier, there are two coupling mechanisms between cavity modes and matter excitons: weak and strong coupling effects . Excitons can be influenced by the cavity electromagnetic field in weak coupling regions .…”