Excitons in semiconductor quantum dots and localized surface plasmons in metallic nanoparticles represent two fundamentally different but highly complementary nanoscale excitations. Quantum dots provide discrete, size-tunable excitonic states with high quantum yields, while plasmonic nanoparticles support subwavelength optical modes with extreme field confinement and ultrafast dynamics. The ability of plasmonic nanostructures to confine, enhance, and redirect light supports their use in sensing, surface-enhanced spectroscopy, antenna-based light manipulation, and ultrafast photonics. When excitonic and plasmonic components are brought together within nanometer distances, their interactions generate a spectrum of coupling phenomena ranging from simple radiative-rate modifications to the emergence of deeply hybridized light–matter states. Hybrid plasmon–quantum dot systems combine these attributes, enabling tailored light–matter interactions that underpin a wide range of applications, including enhanced light emission, single-photon sources, sensing, and nanoscale photonic devices. This Spotlight article surveys the physical principles governing excitons in colloidal quantum dots and plasmons in metallic nanostructures, followed by an overview of the synthesis and design strategies used to construct well-controlled plasmon–quantum dot hybrid architectures. We then review plasmon–exciton interactions within the context of the quantum Rabi model, highlighting how different coupling regimes, from weak and Purcell-enhanced emission to strong, ultrastrong, and deep-strong coupling, emerge depending on the mode volume, loss rates, and coupling strength. A representative weak-coupling example is discussed using CdSe/CdS quantum dots coupled to plasmonic nanostructures, where enhanced radiative decay and suppressed blinking arise without coherent energy exchange. Other recent demonstrations of strong plasmon–exciton coupling, where hybridized polaritonic states and mode splitting are observed, are further described. Together, these examples illustrate how plasmonic nanoparticles provide a versatile platform for accessing and engineering distinct light–matter coupling regimes, offering both practical device functionalities and a testbed for exploring quantum electrodynamical phenomena at the nanoscale.
Gogoi et al. (Thu,) studied this question.