Order of magnitude enhancement of monolayer MoS2 photoluminescence due to near-field energy influx from nanocrystal films

Tianle Guo,Sara M Rupich,Yuri N Gartstein,Kehao Zhang,Yves J Chabal,Anton V Malko,Joshua A Robinson,Siddharth Sampat

doi:10.1038/srep41967

Abstract

Two-dimensional transition metal dichalcogenides (TMDCs) like MoS2 are promising candidates for various optoelectronic applications. The typical photoluminescence (PL) of monolayer MoS2 is however known to suffer very low quantum yields. We demonstrate a 10-fold increase of MoS2 excitonic PL enabled by nonradiative energy transfer (NRET) from adjacent nanocrystal quantum dot (NQD) films. The understanding of this effect is facilitated by our application of transient absorption (TA) spectroscopy to monitor the energy influx into the monolayer MoS2 in the process of ET from photoexcited CdSe/ZnS nanocrystals. In contrast to PL spectroscopy, TA can detect even non-emissive excitons, and we register an order of magnitude enhancement of the MoS2 excitonic TA signatures in hybrids with NQDs. The appearance of ET-induced nanosecond-scale kinetics in TA features is consistent with PL dynamics of energy-accepting MoS2 and PL quenching data of the energy-donating NQDs. The observed enhancement is attributed to the reduction of recombination losses for excitons gradually transferred into MoS2 under quasi-resonant conditions as compared with their direct photoproduction. The TA and PL data clearly illustrate the efficacy of MoS2 and likely other TMDC materials as energy acceptors and the possibility of their practical utilization in NRET-coupled hybrid nanostructures.

Highlights

Our findings indicate that excitonic sensitization of transition metal dichalcogenides (TMDCs) via energy transfer (ET) occuring on a comparatively “slow”, nanosecond, time scale is capable of greatly reducing the recombination losses and dramatically increase the quantum yield of the emissive excitons in monolayer MoS2
An order of magnitude PL enhancement effect of nanocrystal quantum dots (NQDs) on the MoS2 photoluminescence is evident in Fig. 1(d) which shows the ratio of MoS2 PL intensity in hybrid to the reference MoS2 monolayer sample
We have demonstrated that the excitonic sensitization of monolayer MoS2 via energy transfer (ET) from the adjacent NQD films in the NQD/MoS2 hybrid nanostructures results in a nearly 10-fold enhancement of MoS2 emission

Summary

Introduction

The common means to create excitons in monolayer TMDCs are via the direct photon absorption or via the injection of electrons and holes, which respectively lead to the phenomena of photoluminescence (PL)[7] and electroluminescence[8], as experimentally observed in these materials It is known, that recombination losses[9,10] of the excitations photoproduced in monolayer MoS2 can result in substantial limitations on the observed PL emission quantum yield (QY), which is commonly found well below 1% in the as-prepared samples[11]. Our recent observation[25] of quite high, 85%, NRET efficiency from individual (arranged in sub-monolayers) CdSe/CdS NQDs with a large radius that defines the appreciable separation distance of h 10 nm between NQDs and MoS2 monolayers gives further support to the idea of effective excitonic sensitization of TMDCs

Results

Discussion

Conclusion