Strong suppression of emission quenching in core quantum dots coupled to monolayer MoS2

Abstract

Non-radiative processes like energy and charge transfer in 0D–2D semiconductor quantum dot (QD)-transition metal dichalcogenides (TMDs) and other two-dimensional layered materials, like graphene and analogs, leading to strong quenching of the photoluminescence (PL) of the usually highly emissive QDs, have been widely studied. Here we report control of the emission efficiency of core QDs placed in close proximity to the monolayers of MoS₂. The QDs are transferred in the form of a high-density compact monolayer with the dot–dot separation, δ as well as the MoS₂–QD separation, d, being controlled through chemical methods. While at larger separations we observe some quenching due to non-radiative processes, at smaller separations we observe enhanced emission from QDs on MoS₂ as compared to the reference despite the presence of significant non-radiative charge transfer. Interestingly, at small separations δ, we see evidence of strong dot–dot interactions and a significant red shift of QD PL which enhances spectral overlap with the B exciton of MoS₂. However, we observe significant reduction of PL quenching of QDs relative to longer δ and d cases, despite increased probability of non-radiative resonant energy transfer to MoS₂, due to the enhanced spectral overlap, as well as charge transfer. Significantly we observe that simultaneously the intensity of the B exciton of MoS₂ increases significantly suggesting the possibility of coherent and resonant radiative energy exchange between the 0D excitons in QDs and the 2D B exciton in MoS₂. Our study reveals interesting nanoscale light–matter interaction effects which can suppress quenching of QDs leading to potential applications of these nanoscale materials in light emitting and photonic devices.