Excitation and emission distinguished photoluminescence enhancement in a plasmon-exciton intermediate coupling system

Plasmonic nanocavities with tunable resonances provide a powerful platform to manipulate the light-matter interaction at the nanoscale. Here, we investigate the coupling between monolayer MoS2 and the nanocavity formed by a silver nanowire (NW) and a gold film. The splitting of scattering spectra indicates intermediate coupling between the plasmon mode and two exciton states. The coupled system shows a photoluminescence (PL) intensity enhancement of 86-fold for the nanocavity with an appropriate NW diameter. In particular, the excitation and emission enhancement factors are experimentally distinguished, and the simulation results confirm the plasmon resonance dependent excitation and emission enhancements. Moreover, it is shown that the PL emission from the hybrid system becomes strongly polarized, and the degree of linear polarization larger than 0.9 is obtained. These results demonstrate the tunable coupling between plasmon mode and exciton states and help in deepening the understanding of the PL enhancement mechanisms.