Optimizing Strong Coupling of Plasmon-Exciton Hybrids for Largely Enhancing Luminescence

Strong coupling of plasmons and excitons induces intriguing hybridized resonances in absorption and scattering processes but often suffers from poor luminescence efficiency. Here, we demonstrate largely enhanced two-photon luminescence (TPL) of Cy5@AgAl hybrids at ambient conditions by adjusting the resonance strength of radiative plasmons and ensemble excitons (α_p and α_c) and their coupling efficiency (β). The TPL enhancement factor reaches a maximum of 253 at I_AgAl^(TPL)/I_Cy5^(TPL) = 1.1 and when most ensemble excitons have the same large coupling strength with plasmons. The newly developed linear response theoretical model reveals the unique spectral repartitioning induced by hybridized interference during absorption and radiation processes, and the largest radiative enhancement is attributed to the optimized hybridized interference determined by βα_pα_c. Our observations provide a strategy to design active photonic nanodevices with optimized radiation ranging from optically hybridized nanoantennas to quantum information processing.