Homogeneous and inhomogeneous sources of optical transition broadening in room temperature CdSe/ZnS nanocrystal quantum dots

TL;DR

This study investigates the sources of optical transition broadening in room temperature CdSe/ZnS nanocrystal quantum dots, revealing that inhomogeneity and spectral diffusion significantly influence spectral linewidths.

Contribution

It provides a detailed analysis of broadening mechanisms in individual nanocrystals, combining experimental measurements with theoretical modeling to distinguish contributions.

Findings

Phonon broadening is often not the dominant factor at room temperature.

Spectral diffusion varies among quantum-confined states.

Broadening does not necessarily increase with transition energy.

Abstract

We perform photoluminescence excitation measurements on individual CdSe/ZnS nanocrystal quantum dots (NCQDs) at room temperature to study optical transition energies and broadening. The observed features in the spectra are identified and compared to calculated transition energies using an effective mass model. The observed broadening is attributed to phonon broadening, spectral diffusion and size and shape inhomogeneity. The former two contribute the broadening transitions in individual QDs while the latter contributes to the QD-to-QD variation. We find that phonon broadening is often not the dominant contribution to transition line widths, even at room temperature, and that broadening does not necessarily increase with transition energy. This may be explained by differing magnitude of spectral diffusion for different quantum-confined states.