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Nano-sized NaF inspired intrinsic solvothermal growth mechanism of rare-earth nanocrystals for facile control synthesis of high-quality and small-sized hexagonal NaYbF4:Er

Abstract

In an effort to address the solvothermal control synthesis issues of hexagonal upconversion nanocrystals (UCNCs) without additional co-doping, especially for NaYbF4:Er, we find for the first time that the mostly used sodium sources of NaOH and sodium oleate function through totally unexpected NaF-HF pathway rather than the commonly accepted pathway of themselves. Specifically, NaOH reacts with NH4F and converts to nano-sized NaF completely in methanol, leading to reduced NH4F decomposition/HF generation in NaOH based synthesis. By contrast, sodium oleate-oleic acid hybrid occurs to suppress NaF generation, leading to enhanced NH4F decomposition/HF generation in sodium oleate based one. HF-flask SiO2 reaction, HF-to-NaF etching and HF tail gas were also detected for the first time. Results show the nano-sized NaF and in-situ generated HF play key roles in the formation of cubic monomers and the cubic-to-hexagonal transition of UCNCs, respectively. Inspired by these, a facile binary sodium strategy was proposed to achieve control synthesis of high-quality and small-sized hexagonal UCNCs via simultaneous regulation of nano-sized NaF and HF levels. HF was also verified as an origin of Ostwald-ripening for UCNCs. The impacts of Ostwald-ripening on the evolution of UCNCs were thus investigated. Our findings not only offer advanced growth mechanism, but also present an effective control synthesis tool for UCNCs.

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Publication details

The article was received on 10 Jun 2017, accepted on 04 Aug 2017 and first published on 04 Aug 2017


Article type: Paper
DOI: 10.1039/C7TC02573D
Citation: J. Mater. Chem. C, 2017, Accepted Manuscript
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    Nano-sized NaF inspired intrinsic solvothermal growth mechanism of rare-earth nanocrystals for facile control synthesis of high-quality and small-sized hexagonal NaYbF4:Er

    J. Shen, Z. Wang, J. Liu and H. Li, J. Mater. Chem. C, 2017, Accepted Manuscript , DOI: 10.1039/C7TC02573D

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