Plexciton Quenching by Resonant Electron Transfer from Quantum Emitter to Metallic Nanoantenna

Abstract

Coupling molecular excitons and localized surface plasmons in hybrid nanostructures leads to appealing, tunable optical properties. In this respect, the knowledge about the excitation dynamics of a quantum emitter close to a plasmonic nanoantenna is of importance from fundamental and practical points of view. We address here the effect of the excited electron tunneling from the emitter into a metallic nanoparticle(s) in the optical response. When close to a plasmonic nanoparticle, the excited state localized on a quantum emitter becomes short-lived because of the electronic coupling with metal conduction band states. We show that as a consequence, the characteristic features associated with the quantum emitter disappear from the optical absorption spectrum. Thus, for the hybrid nanostructure studied here and comprising quantum emitter in the narrow gap of a plasmonic dimer nanoantenna, the quantum tunneling might quench the plexcitonic states. Under certain conditions the optical response of the system approaches that of the individual plasmonic dimer. Excitation decay via resonant electron transfer can play an important role in many situations of interest such as in surface-enhanced spectroscopies, photovoltaics, catalysis, or quantum information, among others. KEYWORDS: Plexcitons, plasmon, exciton, quantum plasmonics, individual hybrid nanostructures B ringing together metallic nanostructures and quantum emitters, such as quantum dots and molecular complexes, offers unprecedented opportunities in controlling light on the nanoscale. Indeed, the tunability of the plasmonic response and of the near field enhancement in metal nanoparticle assemblies 1−5 allows to engineer the coupling between the excitonic resonance of a quantum emitter (QE) and the collective motion of the metallic electrons, i.e. the plasmons. During the past decade, the study of the interaction between light and these hybrid structures turned into an active field of research 6−25 owing to its fundamental interest and similarity with cavity quantum electrodynamics, 13,19 and due to the vast range of possible applications such as sensing, 26 single photon emitters for information technology, 27,28 and active devices.29−32 With increasing plasmon−exciton coupling strength, when the excitation energy of the emitter is tuned across the plasmon resonance, the Fano profiles in the scattering cross section evolve into the spectral features of avoided crossings 13,14,19,20 with well-resolved mixed states, so-called plexcitons. 21−23 As demonstrated in recent experiments, 23 the near-field enhancement in the junction between nanoparticles 3−5,33 might lead in this system to the strong plasmon−exciton coupling with large Rabi splitting of the issuing plexcitonic states. On the theoretical side, classical and quantum calculations for a QE placed in the middle of the junction of a plasmonic dimer show that the hybrid structure undergoes dramatic changes in the absorption cross section as compared to individual components. [12][13][14][15]23 Thus...

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