Plasmon induced brightening of dark exciton in monolayer WSe<inf>2</inf> for quantum optoelectronics

In the present work, we report plasmon induced brightening of dark excitons (XD) in Au nanoparticle (Au-NP) coated monolayer (1L) WSe2. We observed one order enhancement in photoluminescence (PL) intensity and surface enhanced Raman scattering in Au-NP/1L-WSe2 at room temperature (RT). Temperature dependent PL measurements showed enhanced PL emission from RT down to 100 K in contrast to reduced PL emission which is generally observed for pristine 1L-WSe2. We attribute this effect to the out-of-plane electric field induced by the scattering from Au-NPs, which results in the out-of-plane dipole moment and spin-flip of conduction band electrons in Au-NP/1L-WSe2, making XD bright. Our approach provides a facile way to harness excitonic properties in low-dimensional semiconductors, offering simple strategies for quantum optoelectronics.