MoS2 monolayer quantum dots on a flake: Efficient sensitization of exciton and trion photoluminescence via resonant nonradiative energy and charge transfers

Abstract

MoS2 monolayer quantum dots (1L-QDs) are hybridized on 1L MoS2 on SiO2/Si. The exciton and trion photoluminescence (PL) of the 1L-QD/MoS2 hybrid is studied in comparison to bare 1L MoS2. The 1L-QDs have a round-like shape with an average lateral size of 3 nm, which results in interband absorption and PL within 2.3–3.5 eV. The bare flake shows the A and B exciton PL bands, overlapped with a weak trion band. The 1L-QD/MoS2 hybrid comprises the emission bands so that the 1L-QD PL intensity is not altered, but the flake PL is tremendously enhanced. This effect of sensitization depends on the PL excitation energy: 6.4 times under UV excitation involving the transitions between the valence band and the excited states in the conduction band of the 1L-QDs and 2.7 times under blue light excitation involving interband absorption between the 1L-QD quantum states. The strongest effect is explained by an efficient nonradiative energy transfer (NRET), similar to Förster resonance energy transfer, and possible charge transfer from the resonant levels in the donor 1L-QDs to the levels in the acceptor MoS2 flake. On the contrary, exciting e-h pairs between the 1L-QD quantum states, they rapidly recombine there, weakening NRET.