Phase‐ and Size‐Controllable Synthesis of Hexagonal Upconversion Rare‐Earth Fluoride Nanocrystals through an Oleic Acid/Ionic Liquid Two‐Phase System |
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Authors: | Meng He Dr Peng Huang Dr Chunlei Zhang Jiebing Ma Prof Rong He Prof Daxiang Cui |
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Institution: | Department of Bio‐Nano Science and Engineering, National Key Laboratory of Nano/Micro Fabrication Technology, Key Laboratory for Thin Film and Microfabrication of Ministry of Education, Institute of Micro‐Nano Science and Technology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (P. R. China) |
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Abstract: | Herein, we introduce a facile, user‐ and environmentally friendly (n‐octanol‐induced) oleic acid (OA)/ionic liquid (IL) two‐phase system for the phase‐ and size‐controllable synthesis of water‐soluble hexagonal rare earth (RE=La, Gd, and Y) fluoride nanocrystals with uniform morphologies (mainly spheres and elongated particles) and small sizes (<50 nm). The unique role of the IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BmimPF6) and n‐octanol in modulating the phase structure and particle size are discussed in detail. More importantly, the mechanism of the (n‐octanol‐induced) OA/IL two‐phase system, the formation of the RE fluoride nanocrystals, and the distinctive size‐ and morphology‐controlling capacity of the system are presented. BmimPF6 is versatile in term of crystal‐phase manipulation, size and shape maintenance, and providing water solubility in a one‐step reaction. The luminescent properties of Er3+‐, Ho3+‐, and Tm3+‐doped LaF3, NaGdF4, and NaYF4 nanocrystals were also studied. It is worth noting that the as‐prepared products can be directly dispersed in water due to the hydrophilic property of Bmim+ (cationic part of the IL) as a capping agent. This advantageous feature has made the IL‐capped products favorable in facile surface modifications, such as the classic Stober method. Finally, the cytotoxicity evaluation of NaYF4:Yb,Er nanocrystals before and after silica coating was conducted for further biological applications. |
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Keywords: | ionic liquids luminescence nanocrystals rare earths structure elucidation |
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