The role of the ligand layer for photoluminescence spectral diffusion of CdSe/ZnS nanoparticles

TL;DR

This study investigates how ligand layers influence spectral diffusion in single CdSe/ZnS nanoparticles, revealing that ligand-bound charges cause spectral jitter and linewidth changes, with implications for nanoparticle emission stability.

Contribution

It demonstrates that charges in the ligand layer are responsible for spectral diffusion, providing a quantitative model linking ligand charges to spectral jitter in nanoparticles.

Findings

Spectral jitter up to 55 meV observed in single nanoparticles.

Charge in ligand layer causes spectral diffusion, not core or shell.

Mean charge distance from nanoparticle center is about 3.3 nm.

Abstract

The time-resolved photoluminescence (PL) characteristics of single CdSe/ZnS nanoparticles, embedded in a PMMA layer is studied at room temperature. We observe a strong spectral jitter of up to 55 meV, which is correlated with a change in the observed linewidth. We evaluate this correlation effect using a simple model, based on the quantum confined Stark effect induced by a diffusing charge in the vicinity of the nanoparticle. This allows us to derive a mean distance between the center of the particle and the diffusing charge of approximately 3.3 nm on average, as well as a mean charge carrier displacement within the integration time. The distances are larger than the combined radius of particle core and shell of about 3 nm, but smaller than the overall radius of 5 nm including ligands. These results are reproducible, even for particles which exhibit strong blueing, with shifts of up to 150 meV. Both the statistics and its independence of core-shell alterations lead us to conclude that the charge causing the spectral jitter is situated in the ligands.