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Monolayers of transition-metal dichalcogenides (TMDCs) are recently isolated materials combining strong light-matter interactions and high charge mobilities. Many TMDCs possess direct bandgap - a necessary property for optoelectronic and photonic applications. On the other hand, colloidal semiconductor nanocrystals (NQDs) exhibit high emission efficiency, chemical lability and excellent bandgap tunability via size quantization. Joining the two classes of materials in hybrid structures aims to utilize their respective strengths.
Among those, hybrids where two constituents are coupled via non-radiative energy transfer (NRET) present a particular interest. In the NRET process, exciton energy is transferred from NQD donor to TMDC acceptor via near-field, dipole-dipole energy coupling. This process plays an important role in photosynthetic plants and has been recently considered for energy harvesting in NQD/semiconductor architectures. Its efficiency depends on the distance, spectral overlap and dielectric screening properties of the acceptor material and its dimensionality. With the emergence of 2D materials, there is strong motivation, both for fundamental reasons and for the new applications, to study NRET in these novel systems.
We have studied NRET coupling between several types of NQDs and MoS2 monolayers using photoluminescence (PL) and femtosecond transient absorption (TA) spectroscopies. Both methods indicate very efficient NRET into the MoS2 acceptor, with donor PL intensity quenching concurrent with energy influx into acceptor as observed by TA. These effects are facilitated by reduced dielectric screening inherent to strongly polarizable TMDC materials as described by classical electromagnetic model. We envision energy coupling in 0D-2D hybrids enabling applications in photosensing, photovoltaics and light emission.
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