Enhancement, brightening and control of radiative emission of dark exciton in WSe2 monolayer by plasmonic effect

Abstract Dark excitons in two-dimensional (2D) transition metal dichalcogenide semiconductors (TMDs) have long radiative lifetimes, making them promising for quantum information and optoelectronics. Their detection and control are challenging due to weak out-of-plane dipole moments and momentum mismatch with free-space photons. Using ab initio calculations (DFT + G 0 W 0 + BSE), a Wannier–Mott exciton model, and a numerical solution of the Laplace equation, we model the tip-enhanced near-field and its interaction with excitons via first-order time-dependent perturbation theory. Focusing on WSe 2 monolayers, we show that the strong out-of-plane near field from a metallic tip enhances radiative recombination of spin-forbidden dark excitons by providing additional in-plane momentum to overcome momentum mismatch. We also analyze substrate screening effects on excitonic properties and lifetimes. Our results offer a theoretical framework for controlled activation of dark excitons toward quantum and nanophotonic applications.