Plasmon-Induced Hot-State Multiexciton Emission from Quantum Dots Coupled to Metallic Nanocavities

Nonradiative Auger quenching strongly limits multi-exciton (MX) emission in semiconductor quantum dots (QDs), restricting their performance in high-power photonic and electro-optical applications. We report efficient hot-state MX emission by coupling colloidal QDs into plasmonic aluminum nanohole cavities, manifesting significantly enhanced photoluminescence from the 1P_e-1P_3/2 transition and higher hot MX states, with emission energies up to 500 meV above the band-edge transition. Power-dependent photoluminescence shows up to 15-fold increase of the hot MX emission compared with pristine QDs on glass, at 10-fold lower nominal MX density. At relatively low excitation powers corresponding to an average exciton population of ∼0.3, a significant photoluminescence blue shift is observed, assigned to efficient emission from multiply charged excitons, indicating cavity-induced photo charging of the QD. Investigating the influence of nanohole size, QD location within the cavity, and power and wavelength-dependent excitation establishes the central role of plasmon-induced energy transfer and hot charge injection from the excited metal cavity to the coupled QD, which, alongside plasmonic enhancement of QD absorption and emission, yields the efficient hot MX emission. This mechanism is supported by numerical simulations and comparing metallic cavities differing by their plasmonic spectral response, providing direct evidence for the importance of state filling, through plasmon-driven metal-QD interactions, for hot MX emission. This distinctive ability to activate otherwise quenched MX states allows broadband and tunable emission from individual QDs embedded in nanosized plasmonic cavities, offering a controlled chip-scale approach for color tuning. These findings promote pathways for high-power applications in photocatalysis, tunable microlasers, broadband light sources, and correlated multiphoton sources for quantum technologies.