Photon Upconversion of Defect-Bound Excitons in hBN-Encapsulated MoS Monolayer.

Atomic defects associated with vacancies in two-dimensional transition metal dichalcogenide monolayers efficiently trap charged carriers and strongly localize excitons. Defects in semiconducting monolayers are seldomly utilized for enhancing optical phenomena, although they may provide resonant intermediate states within the energy band gap for applications with multiphoton excitations, like highly efficient and thermally robust photon upconversion. In an MoS monolayer encapsulated by hBN with high defect and resident electron densities, we observe an upconversion of localized exciton (X) emission with a huge energy gain of up to 290 meV.

Biexciton and Singlet Trion Upconvert Exciton Photoluminescence in a MoSe Monolayer Supported by Acoustic and Optical K-Valley Phonons.

Transition metal dichalcogenide monolayers represent unique platforms for studying both electronic and phononic interactions as well as intra- and intervalley exciton complexes. Here, we investigate the upconversion of exciton photoluminescence in MoSe monolayers. Within the nominal transparency window of MoSe the exciton emission is enhanced for resonantly addressing the spin-singlet negative trion and neutral biexciton at a few tens of meV below the neutral exciton transition.