A Large Blue Shift of the Biexciton State in Tellurium Doped CdSe Colloidal Quantum Dots

TL;DR

This study demonstrates a significant blue shift in the biexciton state of tellurium-doped CdSe colloidal quantum dots due to strong Coulomb repulsion, with implications for optical gain applications.

Contribution

It provides the first experimental measurement of a large biexciton blue shift in tellurium-doped CdSe quantum dots and links it to the localized hole wave function.

Findings

Biexciton blue shift up to 300 meV observed.

Biexciton blue shift increases linearly with Stokes shift.

Strong Coulomb repulsion indicates narrow hole wave function.

Abstract

The exciton-exciton interaction energy of Tellurium doped CdSe colloidal quantum dots is experimentally investigated. The dots exhibit a strong Coulomb repulsion between the two excitons, which results in a huge measured biexciton blue shift of up to 300 meV. Such a strong Coulomb repulsion implies a very narrow hole wave function localized around the defect, which is manifested by a large Stokes shift. Moreover, we show that the biexciton blue shift increases linearly with the Stokes shift. This result is highly relevant for the use of colloidal QDs as optical gain media, where a large biexciton blue shift is required to obtain gain in the single exciton regime.