The Tuning of Exciton‐Phonon Coupling in Colloidal Nanocrystals by a Dielectric Medium

Abstract

Here, a thorough study is reported that exposes the influence of surfactants’ dielectric screening on the exciton energy and exciton‐phonon coupling in CdSe and CdSe/CdS colloidal quantum dots and nanoplatelets. The study follows the temperature dependence of the photoluminescence spectrum to monitor thermally activated exciton‐phonon interactions. The dependence of the exciton energy on temperature exhibits an anomalous point at ≈250 K, which coincides with the melting point of surfactant ligands (oleate molecules), an effect that is accompanied by a change in the dielectric constant. Interestingly, this anomalous effect gradually fades away upon increasing the shell thickness in CdSe/CdS derivatives. Furthermore, inspecting the exciton band's full‐width‐at‐half‐maximum (FWHM) dependence on temperature reveals the tuning of the optical phonon frequency when in direct contact with surfactant ligands. However, this effect is replaced by a surplus coupling to the phonon mode of the shell (CdS or CdSeS) when the thickest shell solely isolates the ligand dielectric screening. The study uncovers the impact of the dielectric screening on the optical properties of semiconductor nanocrystals, with an added value in the implementation of those materials in various optoelectronic, quantum, and tagging devices.

Reducing Emission Linewidth of Pure‐Blue ZnSeTe Quantum Dots through Shell Engineering toward High Color Purity Light‐Emitting Diodes

“…The results of narrowed FWHM of LO peak and decreased 2LO/LO intensity ratio also indicate the weakening of exciton-LO phonon coupling. [50][51][52] Therefore, the reduced FWHM in ZnSeTe/ZnSe/ZnS QDs is considered to mainly come from a decrease of homogeneous broadening contribution due to weakened exciton-LO phonon coupling and combine with the suppression of trap emissions with a coating of internal ZnSe shell.…”

Colloidal Control of Branching in Metal Chalcogenide Semiconductor Nanostructures

“…Colloidal chemistry has been long used for obtaining nanostructures of metal chalcogenides in the form of dots, , wires, sheets, platelets, , and many more. Additionally, the growth of the colloidal metal chalcogenides into various branched nanostructures (BNSs) has also been observed, − many times serendipitously.…”

“…However, recent studies on PbS, PbSe, CdS, and CdSe NCs prepared via hot injection have shown that the nucleation phase sometimes overlaps significantly with the growth phase due to extended nucleation and the size-dependent growth leads to narrow size distribution. 3−5 Colloidal chemistry has been long used for obtaining nanostructures of metal chalcogenides in the form of dots, 6,7 wires, 8 sheets, 9 platelets, 10,11 and many more. Additionally, the growth of the colloidal metal chalcogenides into various branched nanostructures (BNSs) has also been observed, 12−16 many times serendipitously.…”