  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
noninteracting. Here, we go beyond the localized Purcell effect to exploit
exciton dynamics. As interacting excitons diffuse through optical hotspots, the
balance of excitonic and nanophotonic properties leads to either enhanced or
suppressed photoluminescence. We identify the dominant enhancement mechanisms
in the limits of high and low diffusion and annihilation to turn their
detrimental impact into additional emission. Our guidelines are relevant for
efficient and high-power light-emitting diodes and lasers based on monolayer
semiconductors, perovskites, or organic crystals.
