  We report highly efficient non-radiative energy transfer from cadmium
selenide (CdSe) quantum dots to monolayer and few-layer molybdenum disulfide
(MoS2). The quenching of the donor quantum dot photoluminescence increases as
the MoS2 flake thickness decreases, with the highest efficiency (>95%) observed
for monolayer MoS2. This counterintuitive result arises from reduced dielectric
screening in thin layer semiconductors having unusually large permittivity and
a strong in-plane transition dipole moment, as found in MoS2. Excitonic energy
transfer between a 0D emitter and a 2D absorber is fundamentally interesting
and enables a wide range of applications including broadband optical
down-conversion, optical detection, photovoltaic sensitization, and color
shifting in light-emitting devices.
