Charge and energy transfer of quantum emitters in 2D heterostructures

Graphene is often used as an acceptor in highly efficient energy transfer processes between its electrons and neighbouring optical emitters such as quantum dots, fluorescent molecules and color centres in crystals. Here we demonstrate that graphene can act not only as an acceptor in energy transfer processes, but also an acceptor of charge donated by photoexcited quantum emitters. Specifically, we use heterostructures comprised of graphene and hexagonal boron nitride (hBN) to demonstrate a reversible charge transfer process from quantum emitters in hBN to graphene. The process acts as a controllable, energy-resolved filter that quenches quantum emitters with ground states located above the Fermi level of graphene. Our findings shed light on the positions of hBN defect states within the bandgap of hBN, and are important for the design of devices based on 2D heterostructures, opening new avenues to technologies based on electrical excitation, manipulation, and readout of the quantum states of optical emitters.