Correlations in the Binding Energy of Triexcitons and Biexcitons in Single CdSe/CdS Nanoplatelets Revealed by Heralded Spectroscopy

TL;DR

This study investigates multiexciton interactions in CdSe/CdS nanoplatelets using heralded spectroscopy, revealing blue-shifted binding energies and pathways for nearly degenerate photon triplet emitters.

Contribution

It introduces a novel spectroscopic approach to resolve triexciton-biexciton interactions and demonstrates their tunability in nanoplatelets, advancing quantum emitter development.

Findings

Blue shift indicates repulsive multiexciton interactions.

Triexciton recombines via 1S bands, not 1P bands.

Strong correlation between biexciton and triexciton binding energies.

Abstract

Semiconductor nanoplatelets present reduced Auger recombination, giving rise to enhanced multiexciton emission. This virtue makes them good candidates to investigate higher-order carrier dynamics, allowing to extract important excitonic properties, such as biexciton and triexciton binding energies that highly influence applications involving high excitation fluxes. Here, we explore triexciton emission, emanating from single core/shell CdSe/CdS nanoplatelets. We apply heralded post-selection of photon triplets using an advanced home-built single-photon spectrometer in order to resolve the triexciton$-$biexciton$-$exciton$-$ground state cascaded relaxation both in time and spectrum, and unambiguously determine the triexciton relaxation route and interaction nature. The results show a characteristic blue shift of the biexciton and triexciton, pointing to repulsive multiexciton interaction in the nanoplatelets under study. The relatively small measured energy shift of the triexciton (5.9 $\pm$ 0.7 meV) indicates that it recombines through the 1S bands rather than the 1P bands, in agreement with findings on other colloidal quantum dot systems. Most importantly, the strong correlation between the biexciton and triexciton binding energies, and the ability to tune them via control of the particle dimensions and composition, paves the way for developing emitters of nearly degenerate photon triplets.