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

## TL;DR

Researchers studied how triexcitons and biexcitons bind in CdSe/CdS nanoplatelets and found a strong correlation between their energies, which could help design better photon emitters.

## Contribution

The study reveals a strong correlation between triexciton and biexciton binding energies and shows how these can be tuned via nanoplatelet dimensions and composition.

## Key findings

- Triexciton binding energy is 5.9 ± 0.7 meV and recombines through 1S bands.
- Biexciton and triexciton exhibit a blue shift, indicating repulsive interactions.
- Nanoplatelet dimensions and composition can tune binding energies for photon triplet emission.

## 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
extraction of 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 postselection
of photon triplets using an advanced home-built single-photon spectrometer
in order to resolve the triexciton–biexciton–exciton–ground
state cascaded relaxation in both 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 ± 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.