Exciton–plasmon coupling: Mechanisms and emerging technologies

Metal–semiconductor heterostructures provide a versatile platform for tuning light–matter interactions at the nanoscale. At the heterostructure interface, excitonic resonances in semiconductors interact with plasmonic fields of metallic nanostructures giving rise to exciton-plasmon coupling (EPC). This coupling controls energy transfer, charge separation and carrier dynamics across the interface. The strength of EPC ultimately dictates the macroscopic optoelectronic response of the hybrid systems. The coupling strength is sensitive to several interdependent parameters, such as electromagnetic field confinement, oscillator strength, nanostructure geometry, and dissipative interactions, giving rise to diverse interaction regimes, from strong to weak, which show distinct physical characteristics. Despite extensive experimental and theoretical progress, a comprehensive understanding of the emergence and evolution of EPC remains elusive, as coherent hybridization, energy/charge transfer and dissipative processes often coexist within the hybrid system. The interplay between these processes manifests in complex spectral signatures like anticrossing, linewidth modification and intensity enhancement, often obscuring the underlying coupling mechanism. In this review, we present a unified perspective on EPC, treating strong, intermediate, and weak coupling within a continuous conceptual framework, ranging from hybrid eigenstates to perturbative modifications of excitonic and plasmonic resonances. This framework provides a basis for linking these ambiguous spectral signatures across coupling regimes to their underlying microscopic processes. The review further links the EPC mechanisms to device performance in functional and scalable technologies like biosensing, photodetection, photovoltaics, and quantum systems. Finally, we evaluate the fundamental and architectural bottlenecks that hinder translation beyond proof-of-concept demonstrations, thus offering a critical design roadmap for the rational design of scalable EPC-based systems. We argue that addressing these constraints requires a shift from demonstration-driven studies to custom designs that prioritize loss engineering, interface control, mechanism-resolved characterization, and scalable architectures treated as primary design parameters.