Exciton Diffusion and Annihilation in Nanophotonic Purcell Landscapes

Excitons spread through diffusion and interact through exciton–exciton annihilation. Nanophotonics can counteract the resulting decrease in light emission. However, conventional enhancement treats emitters as immobile and non-interacting. It neglects exciton redistribution between regions with different enhancements and the increase in non-radiative decay at high exciton densities. Here, the authors went beyond the localized Purcell effect to exploit exciton dynamics and turn their typically detrimental impact into additional emission. As interacting excitons diffuse through optical hotspots, the balance of excitonic and nanophotonic properties leads to either enhanced or suppressed photoluminescence. The dominant enhancement mechanisms are identified in the limits of high and low diffusion and annihilation. Diffusion lifts the requirement of spatial overlap between excitation and emission enhancements, which are harnessed to maximize emission from highly diffusive excitons. In the presence of annihilation, improved enhancement is predicted at increasing powers in nanophotonic systems dominated by emission enhancement. The guidelines are relevant for efficient and high-power light-emitting diodes and lasers tailored to the rich dynamics of excitonic materials such as monolayer semiconductors, perovskites, or organic crystals.