Optical response of lorentzian nanoshells in the quasistatic limit.

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.