Xuedan Ma1 Benjamin Diroll1 Wooje Cho2 Igor Fedin2 Richard Schaller1 3 Dmitri Talapin2 Stephen Gray1 Gary Wiederrecht1

1, Argonne National Laboratory, Lemont, Illinois, United States
2, The University of Chicago, Chicago, Illinois, United States
3, Northwestern University, Evanston, Illinois, United States

Colloidal quasi-two-dimensional nanoplatelets (NPLs) with atomically controlled thickness are promising candidates for many important technologies.[1,2] They represent an interesting nanomaterial for studying the transition from 3D to 1D quantum confined systems. With excitons in NPLs being strongly confined in the thickness direction, an increase in the lateral size of the NPLs and a weakening in the in-plane confinement has complex effects on their excitonic properties.
We investigate photon emission statistics and carrier dynamics of NPLs using single particle spectroscopy.[3] Second-order photon correlation studies of the NPLs reveal a significant increase in the biexciton quantum yield with NPL lateral size. Furthermore, instead of a monotonic increase in the radiative decay rate with the NPL lateral size as predicted by the electric dipole approximation, we observe an anomalous radiative decay rate saturation in large NPLs. This result is a direct indication of giant oscillator strength in NPLs. Our findings have significant implication towards application of NPLs in light amplification and energy harvesting technologies.

[1] S. Ithurria et al. Nat. Mater. 2011, 10, 936-941.
[2] M. Nasilowski et al. Chem. Rev. 2016, 116, 10934-10982.
[3] X. Ma et al. ACS Nano 2017, 11, 9119-9127.