Biexciton Binding Energy and Line width of Single Quantum Dots at Room Temperature

Broadening of multiexciton emission from colloidal quantum dots (QDs) at room temperature is important for their use in high-power applications, but an in-depth characterization has not been possible until now. We present and apply a novel spectroscopic method to quantify the biexciton line width and biexciton binding energy of single CdSe/CdS/ZnS colloidal QDs at room temperature. In our method, which we term cascade spectroscopy, we select emission events from the biexciton cascade and reconstruct their spectrum. The biexciton has an average emission line width of 86 meV on the single-QD scale, similar to that of the exciton. Variations in the biexciton repulsion (E-b = 4.0 +/- 3.1 meV; mean +/- standard deviation of 15 QDs) are correlated with but are more narrowly distributed than variations in the exciton energy (10.0 meV standard deviation). Using a simple quantum-mechanical model, we conclude that inhomogeneous broadening in our sample is primarily due to variations in the CdS shell thickness.

Automated summary

A novel spectroscopic method, cascade spectroscopy, was used to quantify the biexciton line width and binding energy of single CdSe/CdS/ZnS colloidal quantum dots at room temperature. The average emission line width of biexcitons was found to be 86 meV, similar to that of excitons, with variations in biexciton repulsion more narrowly distributed than variations in exciton energy. Inhomogeneous broadening in the sample was primarily attributed to variations in the CdS shell thickness.