Proceedings of nanoGe Spring Meeting 2022 (NSM22)
DOI: https://doi.org/10.29363/nanoge.nsm.2022.001
Publication date: 7th February 2022
Multiply-excited states in semiconductor nanocrystals (NCs) exhibit intriguing physics and are key in nanocrystal-based quantum technologies. While simultaneous multiple photon emission is typically quenched in quantum dots, in nanoplatelets (NPLs) its probability can be tuned according to size and shape. In particular, multiple excitons strongly bound in just one dimension are free to re-arrange in the lateral plane, reducing the probability for multi-body collisions. In this work, we analyze multi-exciton dynamics in two-dimensional CdSe/CdS core/shell NPLs of various sizes through the measurement of second-, third-, and fourth-order photon correlations.1 Thus, for the first time, we could directly probe the dynamics of the two, three, and four exciton states at the single NC level. Remarkably, although higher orders of correlation vary substantially among a NPLs sample, they strongly correlate with the value of second-order antibunching. The scaling of the higher-order moments with the degree of antibunching presents a small yet clear deviation from the accepted model of Auger recombination through binary collisions. This deviation suggests that many-body contributions are present already at the level of tri-excitons.
In addition, multi-exciton interactions can be visually expressed in the emission patterns of different excitonic states. Type-II ZnSe/CdS dot-in-rod NCs, presenting a dipole radiation pattern due to anisotropy, can be used to demonstrate this phenomenon. A defocused imaging setup coupled to a novel single-photon avalanche detector (SPAD) array containing 23 pixels makes it possible to directly observe and analyze the out-of-focus dipole emission patterns of single excitons and bi-excitons in a single NC, allowing a deeper understanding of the underlying multi-exciton dynamics in semiconductor NCs.
The authors would like to thank Maria Chekhova for helpful discussions, and Ivan Michel Antolovic and Harald Homulle for a fruitful collaboration and assistance with the SPAD23 system.
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