Unified treatment of scattering, absorption, and luminescence spectra from a plasmon–exciton hybrid by temporal coupled-mode theory

Plasmonic nanostructures are capable of tailoring the emission of a nearby emitter by increasing (or reducing) the brightness, shortening (or prolonging) the lifetime, and shaping the spectrum. Experimental characterization of such coupled plasmon–exciton (plexciton) systems usually relies on the acquisition and comparison of scattering, absorption, or luminescence spectra. However, theoretical accounts of these optical spectra, which are key to distinguishing between the coupling regimes and to standardizing the coupling criteria, often scatters in different frameworks, varying from classical to quantum-mechanical. Therefore, developing a unified and simple formalism that can simultaneously compare all these spectral signatures in different coupling regimes is nontrivial. Here, we use a temporal coupled-mode formalism to reproduce the scattering, absorption, and luminescence spectra of a plexciton system and find that its luminescence reaches a maximum at a critical coupling point, featuring a light-emitting plexciton with intense brightness and ultrafast lifetime. This simple approach provides a unified and phenomenological treatment of these spectra by simply including or excluding an external driving term. It therefore allows for a direct comparison of different spectroscopic signatures from the plexciton system and provides an easy-to-use guidance for the design of broadband light-emitting devices.