Comparison between trion and exciton electronic properties in CdSe and PbS nanoplatelets

TL;DR

This study compares the electronic and optical properties of trions and excitons in CdSe and PbS nanoplatelets, revealing how additional charges affect emission energies and oscillator strengths, with implications for optoelectronic applications.

Contribution

It provides a detailed theoretical analysis of trion versus exciton properties in nanoplatelets, incorporating dielectric effects and electronic correlations using advanced computational methods.

Findings

Trions suppress the giant oscillator strength of neutral excitons.

Both negative and positive trions are redshifted compared to excitons.

Emission energy of trions increases with dielectric mismatch.

Abstract

The optoelectronic properties of metal chalcogenide colloidal nanoplatelets are often interpreted in terms of excitonic states. However, recent spectroscopic experiments evidence the presence of trion states, enabled by the slow Auger recombination in these structures. We analyze how the presence of an additional charge in trions modifies the emission energy and oscillator strength as compared to neutral excitons. These properties are very sensitive to dielectric confinement and electronic correlations, which we describe accurately using image-charge and variational Quantum Monte Carlo methods in effective mass Hamiltonians. We observe that the giant oscillator strength of neutral excitons is largely suppressedin trions. Both negative and positive trions are redshifted with respect to the exciton, and their emission energy increases with increasing dielectric mismatch between the platelet and its surroundings, which is a consequence of the self-energy potential. Our results are consistent with experiments in the literature, and assess on the validity of previous theoretical approximations.