The emission efficiency of interlayer excitons (IEs) in twisted 2D heterostructures has long suffered from momentum mismatch, limiting their applications in ultracompact excitonic devices. Here, we report strong room-temperature emission of momentum-forbidden IE in 30°-twisted MoS2/WS2 heterobilayers. Utilizing a plasmonic nanocavity, the Purcell effect boosts the IE emission intensity in the cavity by over 2 orders of magnitude. We further study the interplay of this Purcell enhancement and phonon assistance in 30°- and 0°-twisted heterostructures. Temperature-dependent and time-resolved spectroscopy reveal that the IE enhancement in 30°-twisted cases involves competition between IEs and intralayer excitonic emission, which is remarkably distinct from the 0°-twisted cases. We propose a comprehensive exciton decay model capturing the features of the phonon-assisted momentum compensation and the Purcell enhancement of the IE emission, showing consistency with the experimental measurements. Our results enrich the understanding of the nanocavity-assisted light-matter interaction for momentum-indirect excitonic transitions.
Keywords: Purcell effect; heterostructure; interlayer exciton; momentum mismatch; twist angle.