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首页> 外文期刊>Nanotechnology >A single-step synthesis and the kinetic mechanism for monodisperse and hexagonal-phase NaYF4:Yb, Er upconversion nanophosphors
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A single-step synthesis and the kinetic mechanism for monodisperse and hexagonal-phase NaYF4:Yb, Er upconversion nanophosphors

机译：单分散和六方相NaYF4：Yb，Er上转换纳米磷的一步合成及动力学机理

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摘要

A single-step synthesis for monodisperse and hexagonal-phase (beta) NaYF4:Yb, Er upconversion nanophosphors (UCNPs) with a consistent hexagonal prism shape in the size range from 18 to 200 nm was achieved. The kinetic mechanisms for the particle phase transition and growth were examined. The beta-UCNPs were obtained via co-thermolysis of trifluoroacetate precursors in octadecene (ODE) with combined ligands of oleic acDE (OA) and trioctylphosphine (TOP). The experimental results showed that the combined OA-TOP ligand was crucial for changing the surface energy and controlling the particle shape over a broad size range. It was found that the particle sizes could be controlled by varying the molar ratios of Na(CF3COO)/Re(CF3COO)(3) (Re = Y, Yb, and Er). A high Na/Re ratio accelerated the cubic-phase (alpha) -> beta transition and promoted the growth of smaller beta-UCNPs. The formation of beta-UCNPs was classified into kinetic and diffusion controlled stages, depending on the reaction temperature and the dominant crystalline phases formed in each stage. In stage I, 250-310 degrees C, NaF generation was the limiting step and alpha-UCNPs were formed via a 'burst of nucleation'. In stage II, above 310 degrees C, the alpha-UCNPs formed were re-dissolved and the growth of beta-UCNPs was a diffusion controlled process governed by the Gibbs-Thompson effect. A quasi-steady-state species assumption for NaF and a chemical potential equilibrium in the solution were introduced to explain the particle size dependence on Na/Re ratios. The study of UC luminescence showed that the UC intensity was proportional to the sizes of the beta-UCNPs.
机译：实现了单分散和六方相（β）NaYF4：Yb，Er上转换纳米磷光体（UCNP）的一步合成，其尺寸在18至200 nm范围内具有一致的六棱柱形状。检查了粒子相变和生长的动力学机理。 β-UCNPs是通过在十八碳烯（ODE）中与油酸acDE（OA）和三辛基膦（TOP）的结合配体共热解三氟乙酸盐前体而获得的。实验结果表明，组合的OA-TOP配体对于改变表面能和在较大尺寸范围内控制颗粒形状至关重要。发现可以通过改变Na（CF 3 COO）/ Re（CF 3 COO）（3）（Re ＝ Y，Yb和Er）的摩尔比来控制粒径。高的Na / Re比可加速立方相（α）->β的转变，并促进较小的β-UCNP的生长。 β-UCNPs的形成可分为动力学和扩散控制两个阶段，具体取决于反应温度和每个阶段形成的主要结晶相。在第一阶段，即250-310摄氏度，NaF的生成是限制性步骤，并且通过“成核爆发”形成了α-UCNP。在第二阶段，高于310摄氏度，形成的α-UCNP被重新溶解，β-UCNP的生长是由吉布斯-汤普森效应控制的扩散过程。介绍了NaF的准稳态物种假设和溶液中的化学势平衡，以解释颗粒大小对Na / Re比率的依赖性。 UC发光的研究表明，UC强度与β-UCNP的大小成正比。

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