Plasmon induced brightening of dark exciton in monolayer WSe2 for quantum optoelectronics

Abstract

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.

Plasmonic Nanocavity Induced Coupling and Boost of Dark Excitons in Monolayer WSe2 at Room Temperature

“…In the absence of external magnetic field, inplane light emission from the dark excitons in ML-WSe 2 was observed using an edge excitation and observation, confirming their out-of-plane dipolar nature. 25 Plasmonic methods have also been recently utilized to observe dark excitons through out-of-plane near-field coupling with either the propagating surface plasmon polaritons (SPPs) on a silver mirror, 26 localized surface plasmons in gold nanoparticles, 28 or a gold nanotip-on-mirror cavity. 19 However, these approaches are bottlenecked by extreme experimental conditions, such as cryogenic temperatures, 17,22,25,26 ultrahigh in-plane magnetic field, 17,22,27 and subnanometer-scale control of the tip−mirror distance, 19 making their implementation somewhat cumbersome.…”

Anomalously polarised emission from a MoS2/WS2heterostructure

“…[26][27][28][29][30] Plasmon induced brightening of dark excitons in TMDC monolayer has also been reported. [31] In doped TMD layers, trions (charged excitons) are also formed along with excitons. The application of a magnetic field has been shown to brighten the corresponding dark (charged) excitons.…”

Stacking angle dependent multiple excitonic resonances in bilayer tungsten diselenide

“…Since RT PL spectra were found to be insensitive to stacking angle, temperature dependent PL measurements down to 100 K, were carried out on these BL systems and the corresponding spectra are shown in Fig.S3. It was observed that, with the reduction in temperature, there was a blue shift and a gradual reduction in the PL intensity of 1L as well as all the BL-WSe 2 systems, which can be attributed to the presence of optically dark exciton in WSe 2 [46,47]. Further, at temperatures below 150 K, the PL line shape of asymmetrically and symmetrically stacked BL-WSe 2 systems were different.…”