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

MoS2 monolayer quantum dots (1L-QDs) are hybridized on 1L MoS2 on SiO2/Si. The exciton and trion photo-luminescence (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 Fo & BULL;rster 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.