Roles of Surface-Ligand and Core-Shell Interfaces in Quantum Dot Fluorescence at the Ensemble and Single Nanoparticle Level

by Omogo, Benard O.; Aldana, Jose F.; Kaneko, Mizuho; Gao, Feng; Heyes, Colin D.

Due to the high surface-to-vol. ratio of nanoparticles, the fluorescence of quantum dots (QDs) is strongly affected by the various interfaces present. Simple core-only QDs have an inorg.-org. surface-ligand interface, while core-shell quantum dots have, in addn., inorg.-inorg. core-shell interfaces. Synthetic parameters are systematically varied, such as stoichiometry, shell thickness, temp., ligand and solvent, to tune the interfaces of CdTe, CdTe-ZnSe, and CdSe, CdSe-CdS, CdSe-ZnS and CdSe-CdS-ZnS. Then, the optical and structural properties are analyzed by a combination of time-resolved fluorescence spectroscopy, single-particle fluorescence microscopy, quant. FT-IR absorption spectroscopy, X-ray photoelectron (XPS) spectroscopy and high-resoln. TEM/HAADF-STEM/EELS microscopy. The connection between the structural details of the interfaces and the quantum yield, radiative and non-radiative excited state decay rates, ligand binding and fluorescence blinking will be discussed to help devise strategies to synthesize QDs tailored for various applications.