Optical Response of Lorentzian Nanoshells in the Quasistatic Limit

Abstract

Recently, plexcitonic systems consisting of a plasmonic nanoshell or a core covered by an excitonic shell are engineered. Such systems hold promise for tunable nanophotonic devices for imaging, chemical sensing, and resonance energy transfer. Their plasmonic response is grasped well, while understanding of their excitonic response remains to be improved. To this end, we have developed a methodology in which the functionalities of the dispersive properties of the spherical shell and the nanoenvironment in tuning the optical response are clearly separated. Using this methodology, we have studied the response of the Lorentzian/excitonic nanoshells with optically inactive core and embedding medium and compared it with the well-known properties of the Drude/plasmonics nanoshells. Contrary to Drude nanoshells exhibiting a resonance pair red-shifted with respect to the bulk, Lorentzian nanoshells are identified by a resonance pair blue-shifted with respect to the in-solution excitonic resonance. While the Drude red-shifting is more effective at increasing dielectric constants (core, shell, and embedding medium), the Lorentzian blue-shifting is governed by the excitonic strength and is suppressed at increasing dielectric constants. The implications of the results for manipulating the optical response of plexcitonic systems are briefly discussed.

Plasmon–Exciton Interactions in a Core–Shell Geometry: From Enhanced Absorption to Strong Coupling

“…To understand the core–shell modes, it is necessary to look at the optical properties of Lorentz-material spheres and shells. Dye spheres and shells have for f < 1 one or two resonances, respectively, although the second resonance for the shell appears when the real part of the permittivity becomes negative enough (see Figure S2). For the shell, one resonance remains at the exciton position (slight blue-shift) and the second weak one blue-shifts with increasing f .…”

Hybridised exciton–polariton resonances in core–shell nanoparticles

“…where f is the reduced oscillator strength, ω 0 is the central (angular) frequency of the resonance, ω is the angular frequency, and γ is the damping rate of the resonance. Substitution of Equation ( 7) into Equation ( 6) with re-arrangement for ω gives two solutions for the resonant frequencies (ω) in the limit that γ ω; these can be written as [29],…”

Subdiffraction Light Concentration by J-Aggregate Nanostructures

“…28,29 The response of Lorentzian/excitonic nanoshells with an optically inactive core and embedding medium has been also studied in the quasistatic limit and compared with the properties of the Drude/plasmonic nanoshells. 30 Recently, it has been theoretically shown that a nanosphere of TDBC-doped PVA displays enhanced optical fields and subwavelength field confinement analogously to plasmonic nanoparticles. 31 At present, however, spherical nanoparticles of J-aggregates have not been realized and the synthesis of high-quality nanospheres does not seem readily achievable.…”

“…It may also occur in the high-energy tail of a strong absorption resonance. For example, it has been shown that lattice vibrations in polar dielectric materials can also originate negative dielectric permittivity in the far- or mid-infrared spectral range, which can support phonon-polaritons confined to the surface. , It has also been shown that in the near-infrared and optical spectral ranges sharp excitonic resonances in organic molecules can originate spectral regions where the dielectric permittivity is negative. , The response of Lorentzian/excitonic nanoshells with an optically inactive core and embedding medium has been also studied in the quasistatic limit and compared with the properties of the Drude/plasmonic nanoshells . Recently, it has been theoretically shown that a nanosphere of TDBC-doped PVA displays enhanced optical fields and subwavelength field confinement analogously to plasmonic nanoparticles .…”