Epitaxial Growth of Highly Luminescent CdSe/CdS Core/Shell Nanocrystals with Photostability and Electronic Accessibility

TLDR

The authors report the synthesis of epitaxially grown wurtzite CdSe/CdS core/shell nanocrystals. Shells up to three monolayers were grown on 23–39 Å cores with sub‑monolayer precision, verified as uniform and epitaxial by XPS, XRD, HRTEM, and optical spectroscopy. The shell growth induces a red‑shift, boosts room‑temperature photoluminescence quantum yield to at least 50%, enhances photostability, and results in hole confinement to the core and electron delocalization, providing electronic accessibility for optoelectronic applications.

Abstract

The synthesis of epitaxially grown, wurtzite CdSe/CdS core/shell nanocrystals is reported. Shells of up to three monolayers in thickness were grown on cores ranging in diameter from 23 to 39 Å. Shell growth was controllable to within a tenth of a monolayer and was consistently accompanied by a red shift of the absorption spectrum, an increase of the room temperature photoluminescence quantum yield (up to at least 50%), and an increase in the photostability. Shell growth was shown to be uniform and epitaxial by the use of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and optical spectroscopy. The experimental results indicate that in the excited state the hole is confined to the core and the electron is delocalized throughout the entire structure. The photostability can be explained by the confinement of the hole, while the delocalization of the electron results in a degree of electronic accessibility that makes these nanocrystals attractive for use in optoelectronic devices.