Efficient light upconversion via resonant exciton-exciton annihilation of dark excitons in few-layer transition metal dichalcogenides

TL;DR

This study demonstrates efficient light upconversion in few-layer transition metal dichalcogenides through resonant exciton-exciton annihilation of dark excitons, enabling tunable emission from green to ultraviolet.

Contribution

It provides a combined theory and experimental demonstration of a new upconversion mechanism involving dark excitons in 2D materials.

Findings

High upconversion efficiency observed in MoS2, MoSe2, WS2, and WSe2.

Upconversion emission tunable from green to ultraviolet.

Resonant exciton-exciton annihilation identified as the key process.

Abstract

In this work, we report a pronounced light upconversion in few-layer transition metal dichalcogenides. Our joint theory-experiment study attributes the upconversion photoluminescence to a resonant exciton-exciton annihilation involving a pair of dark excitons with opposite momenta, followed by the spontaneous emission of upconverted bright excitons, which can have a high upconversion efficiency. Additionally, the upconversion photoluminescence is generic in MoS2, MoSe2, WS2, and WSe2, showing a high tuneability from green to ultraviolet light.