Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2

Abstract

Photon upconversion is an anti-Stokes process in which an absorption of a photon leads to a reemission of a photon at an energy higher than the excitation energy. The upconversion photoemission has been already demonstrated in rare earth atoms in glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate a room temperature upconversion photoluminescence process in a monolayer semiconductor WS₂, with energy gain up to 150 meV. We attribute this process to transitions involving trions and many phonons and free exciton complexes. These results are very promising for energy harvesting, laser refrigeration and optoelectronics at the nanoscale.

Two-dimensional materials show promise for photon upconversion processes due to their strong photon-exciton and phonon-exciton interactions. Here, the authors report room temperature upconversion photoluminescence in monolayer WS₂ with high energy gain up to 150 meV based on variable temperature.