Deciphering Charging Status, Absolute Quantum Efficiency, and Absorption Cross Section of MultiCarrier States in Single Colloidal Quantum Dot

TL;DR

This study provides detailed insights into the charge states, absorption cross sections, and quantum efficiencies of mono- and biexciton states in single colloidal quantum dots, revealing how charge addition influences their optical properties.

Contribution

It introduces a method for in-situ analysis of charge states and precise measurement of optical parameters in single quantum dots, advancing understanding of their multi-carrier states.

Findings

Different photon statistics for charge states in single QDs.

Charge sign identification via photoluminescence decay.

Charge addition alters absorption cross section and emission properties.

Abstract

Upon photo- or electrical-excitation, colloidal quantum dots (QDs) are often found in multi-carrier states due to multi-photon absorption and photo-charging of the QDs. While many of these multi-carrier states are observed in single-dot spectroscopy, their properties are not well studied due to random charging/discharging, emission intensity intermittency, and uncontrolled surface defects of single QD. Here we report in-situ deciphering the charging status, and precisely assessing the absorption cross section, and determining the absolute emission quantum yield of mono-exciton and biexciton states for neutral, positively-charged, and negatively-charged single core/shell CdSe/CdS QD. We uncover very different photon statistics of the three charge states in single QD and unambiguously identify their charge sign together with the information of their photoluminescence decay dynamics. We then show their distinct photoluminescence saturation behaviors and evaluated the absolute values of absorption cross sections and quantum efficiencies of monoexcitons and biexcitons. We demonstrate that addition of an extra hole or electron in a QD changes not only its emission properties but also varies its absorption cross section.