Sequential Growth of High Quality Sub-10 nm Core–Shell Nanocrystals: Understanding the Nucleation and Growth Process Using Dynamic Light Scattering

Abstract

Monodisperse sub-10 nm core–shell nanocrystals have been extensively studied owing to their important applications in catalysis, bioimaging, nanomedicine, and so on. In this work, an amorphous shell component crystallization strategy has been proposed to prepare high quality sub-10 nm NaYF4:Yb/Er@NaGdF4 core–shell nanocrystals successfully via a sequential growth process. The dynamic light scattering technique has been used to investigate the secondary nucleation and growth process forming the core–shell nanocrystals. The size and morphology evolution of the core–shell nanocrystals reveals that the secondary nucleation of the shell component is unavoidable after hot-injecting the shell precursor at high temperatures, which was followed by dissolution and recrystallization (an Ostwald ripening process) to partially produce the core–shell nanocrystals. The present study demonstrates that the size of seed nanocrystals and the injection temperature of the shell component precursor play a vital role in the formation of core–shell nanostructures completely. This work will provide an alternative strategy for precisely controlling the fabrication of sub-10 nm core–shell nanostructures for various applications.

Interfacial Nucleation Mechanism of Water-Soluble Ag–In–S Quantum Dots at Room Temperature and Their Visible Light Catalytic Performance

“…It is worth noting that the PL intensity of AIS QDs is not high because the driving force of the interface reaction is much less than that of high-temperature heating, and the synthesis of AIS QDs leads to core-QDs, in which there are many surface defects. 51,52 The corresponding UV−vis absorption spectra were similar to previous spectra, with no characteristic absorption peak, indicating that no magic-size clusters were generated during the binding process to grow directly into AgInS 2 QDs from the precursor compound (Figure 1d). As a comparison, we used CA as the ligand and used CA to adjust the concentration of hydrogen ions.…”

The Formation of NaYF4 : Er3+, Yb3+ Nanocrystals Studied by In Situ X‐ray Scattering: Phase Transition and Size Focusing

“…The studies involve, for example, ex situ electron microscopy and X-ray scattering/diffraction on aliquots taken during synthesis. [25][26][27][28] Such techniques provide insight into the intermediate stages of the reaction, but they offer limited time resolution and limited possibilities for quantitative analysis. Other studies have used in situ photoluminescence to study the growth mechanism from α-NaREF 4 to β-NaREF 4 NCs, [26,27] which enhances the time resolution but quantitative interpretation remains difficult.…”

“…The intriguing formation of large monodisperse β‐NaREF 4 NCs from smaller α‐NaREF 4 precursor particles has triggered studies into the growth mechanism. The studies involve, for example, ex situ electron microscopy and X‐ray scattering/diffraction on aliquots taken during synthesis [25–28] . Such techniques provide insight into the intermediate stages of the reaction, but they offer limited time resolution and limited possibilities for quantitative analysis.…”

Solvothermal synthesis and modification of NaYF4:Yb/Er@NaLuF4:Yb for enhanced up-conversion luminescence for bioimaging

“…This way, the upconversion luminescence efficiency could be further improved. [25][26][27][28][29][30] For example, Chow et al 31 prepared NaYF 4 :Yb, Er@NaYF 4 :Yb,Tm nanocrystals, and demonstrated that the core-shell structure increased the quantum efficiency by anywhere from 7 to 29 times. Li Fuyou et al 32 demonstrated that a core-shell structure reduced cross-relaxation and surface quenching effects by introducing a CaF 2 layer to improve the upconversion emission.…”