Unusual energy transfer from lower-to-higher bandgap 2D materials in ambient conditions

The interplay of strong spin-orbital coupling and inversion symmetry breaking in a Transition Metal Dichalcogenides (TMDC) monolayer induces strong K (K-) valleys spin splitting, yielding two distinct excitonic resonances. While Charge Transfer (CT) and Energy Transfer (ET) phenomena in TMDC heterostructures have been studied extensively, resonant ET between A and B excitons in heterobilayers is less explored. Our investigations reveal resonant exciton transfer from a lower bandgap monolayer WSe2 to higher bandgap monolayer WS2 with a few layers of hBN spacing. Through the excitation at higher energy excitonic states of WSe2, many excitons decay in the B exciton state and subsequently resonantly transfer to the A exciton state of WS2. This resonant ET, distinct from recently reported unconventional ET in TMDC heterostructures at low temperature, eliminates the need for cooling to suppress electron-phonon scattering, enabling an efficient energy transfer process. Our findings offer a novel perspective on utilizing the diverse excitonic responses within TMDC heterostructures for potential applications in optoelectronics and photonics.