Monodisperse Hexagonal Pyramidal and Bipyramidal Wurtzite CdSe-CdS Core–Shell Nanocrystals

Abstract

Heterostructural core–shell quantum dots (hetero-QDs) have garnered a copious amount of research effort for not only scientific advances but also a range of technological applications. Particularly, controlling the heteroshell deposition, which in turn determines the particle morphology, is vital in regulating the photophysical properties and the application potential of the hetero-QDs. In this work, we present the first report on a synthesis of pyramidal shaped (i.e., hexagonal pyramid, HP, and hexagonal bipyramid, HBP) CdSe-CdS hetero-QDs with high morphological uniformity and epitaxial crystallinity through a two-step shell growth method. The stabilization of the exposed (0002) and {101̅1} facets by octadecylphosphonic acid and oleic acid ligands, respectively, is the key for the formation of pyramidal particle shapes. High photoluminescence quantum yield (94%, HP-QDs and 73%, HBP-QDs), minimal inhomogeneous PL line width broadening, and significantly suppressed single-QD blinking are observed. Specifically, the “giant” HBP-QDs showed an average “On” time fraction of 96% with more than 50% of measured particles completely nonblinking. Additionally, high multiexciton emission, prolonged ensemble and single-QD PL lifetimes as compared to their spherical counterparts are also reported. Finally, the HBP-QDs have been successfully transferred into an aqueous solution without aggregation. High cellular uptakes associated with low cytotoxicity render these water-soluble HBP-QDs an excellent candidate for intracellular imaging and labeling.

Electrochemically-stable ligands bridge the photoluminescence-electroluminescence gap of quantum dots

“…In addition to the ligand systems discussed above, there are some other common types of ligands for colloidal QDs, including organophosphines 5,10,15 , metal phosphonates 39,40 , and thiols 2 . Figure 4e illustrates the photoluminescence-electroluminescence efficiency comparison for both CdSe/CdS core/shell and CdSe/ CdS/ZnS core/shell/shell QDs with different ligands.…”

A Ligand System for the Flexible Functionalization of Quantum Dots via Click Chemistry

“…Quantum dots (QDs) are promising fluorescent probes in biomedical imaging research due to their high quantum yield (QY), good photo‐stability, broad absorption, and tunable and narrow photoluminescence (PL) spectra . To enable their biological applications, the as‐synthesized hydrophobic QDs need to be transferred into aqueous solutions through surface modifications.…”

Investigation of the photophysical properties of energy-relevant inorganic nanocrystals

“…Many of these core/shell particles have a relatively inhomogeneous shell, which is consistent with well-documented studies on CdSe/CdS core/shell nanocrystals. [115][116][129][130][131] As in the classical CdSe/CdS system, inhomogeneous surface coverage in Ge1-xSnx /CdS core/shell nanocrystals is not an immediate problem, at least in terms of ensemble optical properties, as it is able to provide enough surface passivation to enhance and stabilize PL compared to the bare Ge1-xSnx cores. High resolution high-angle annular dark-field (HAADF) STEM images of a Ge0.75Sn0.25/CdS nanocrystals (Figure S5) show the presence of continuous lattice fringes throughout each particle.…”

“…Ge-based nanocrystals that may be useful for energy-related applications such as photovoltaics, light emitting devices (LEDs) or, with appropriate surface passivation, [115][116] as near-infrared active luminescent biological markers.…”