1 research outputs found
Plexcitons: The Role of Oscillator Strengths and Spectral Widths in Determining Strong Coupling
Strong
coupling interactions between plasmon and exciton-based
excitations have been proposed to be useful in the design of optoelectronic
systems. However, the role of various optical parameters dictating
the plasmon-exciton (plexciton) interactions is less understood. Herein,
we propose an inequality for achieving strong coupling between plasmons
and excitons through appropriate variation of their oscillator strengths
and spectral widths. These aspects are found to be consistent with
experiments on two sets of free-standing plexcitonic systems obtained
by (i) linking fluorescein isothiocyanate on Ag nanoparticles of varying
sizes through silane coupling and (ii) electrostatic binding of cyanine
dyes on polystyrenesulfonate-coated Au nanorods of varying aspect
ratios. Being covalently linked on Ag nanoparticles, fluorescein isothiocyanate
remains in monomeric state, and its high oscillator strength and narrow
spectral width enable us to approach the strong coupling limit. In
contrast, in the presence of polystyrenesulfonate, monomeric forms
of cyanine dyes exist in equilibrium with their aggregates: Coupling
is not observed for monomers and H-aggregates whose optical parameters
are unfavorable. The large aggregation number, narrow spectral width,
and extremely high oscillator strength of J-aggregates of cyanines
permit effective delocalization of excitons along the linear assembly
of chromophores, which in turn leads to efficient coupling with the
plasmons. Further, the results obtained from experiments and theoretical
models are jointly employed to describe the plexcitonic states, estimate
the coupling strengths, and rationalize the dispersion curves. The
experimental results and the theoretical analysis presented here portray
a way forward to the rational design of plexcitonic systems attaining
the strong coupling limits