Optical control of charged exciton states in tungsten disulfide

TL;DR

This paper introduces an optical method to selectively excite charged excitons in tungsten disulfide monolayers, enabling controlled luminescence and the study of excitonic states in 2D materials.

Contribution

A novel optical technique to prepare WS2 monolayers in a charged exciton state, allowing for controlled luminescence and isolation of excitonic processes.

Findings

Selective excitation of charged excitons achieved

Luminescence from neutral excitons suppressed

Reversibility of the state with air exposure

Abstract

A method is presented for optically preparing WS2 monolayers to luminesce from only the charged exciton (trion) state--completely suppressing the neutral exciton. When isolating the trion state, we observed changes in the Raman A1g intensity and an enhanced feature on the low energy side of the E12g peak. Photoluminescence and optical reflectivity measurements confirm the existence of the prepared trion state. This technique also prepares intermediate regimes with controlled luminescence amplitudes of the neutral and charged exciton. This effect is reversible by exposing the sample to air, indicating the change is mitigated by surface interactions with the ambient environment. This method provides a tool to modify optical emission energy and to isolate physical processes in this and other two-dimensional materials.