Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, British Columbia, Canada V8W 3V6.
Nanoscale. 2011 Aug;3(8):3376-84. doi: 10.1039/c1nr10317b. Epub 2011 Jul 14.
Lanthanide fluoride nanoparticles were synthesized in aqueous media using procedures intended for a core-shell structure of Ln((1))F(3)-Ln((2))F(3), its reverse architecture, and an alloy structure. Their structures were examined by variable photon energy photo-electron spectroscopy using synchrotron radiation, along with X-ray powder diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and luminescence spectroscopy. The results show that the nanoparticles intended for a core-shell structure do not have a core-shell structure, and that nanoparticles intended for an alloy structure do not always have an alloy structure. A possible explanation for this is cation exchange, a phenomenon that occurs when LnF(3) nanoparticles are exposed to another Ln(3+) ion in aqueous media, resulting in Ln(3+) ions in nanoparticles being quickly replaced by Ln(3+) ions in solution. This cation exchange effectively competes with the precipitation of LnF(3), which leads to a concentration gradient in the case of the combination of LaF(3) and GdF(3), and to nearly an alloy structure (isotropic mixture of all the ions) in the case of the combination of LaF(3) and NdF(3), regardless of the procedure used. Finally, the intended "core-shell" nanoparticles were doped with Eu(3+) to show that a non-core-shell structure can also give rise to the improvement of optical properties as compared with the corresponding core nanoparticles. These results suggest that conclusions in the literature that a core-shell structure was obtained as inferred by TEM or enhanced luminescence may not be correct.
镧系氟化物纳米粒子在水相介质中通过程序合成，目的是获得 Ln((1))F(3)-Ln((2))F(3)的核壳结构、其反转结构和合金结构。采用同步辐射可变光子能量光电子能谱法、X 射线粉末衍射法、透射电子显微镜法、能谱分析法和荧光光谱法对其结构进行了研究。结果表明，设计为核壳结构的纳米粒子不具有核壳结构，而设计为合金结构的纳米粒子并不总是具有合金结构。对此可能的解释是阳离子交换，当 LnF(3)纳米粒子暴露于水相介质中的另一个 Ln(3+)离子时发生阳离子交换现象，导致纳米粒子中的 Ln(3+)离子被溶液中的 Ln(3+)离子迅速取代。这种阳离子交换有效地与 LnF(3)的沉淀竞争，导致在 LaF(3)和 GdF(3)的组合情况下形成浓度梯度，而在 LaF(3)和 NdF(3)的组合情况下形成近乎合金结构（所有离子的各向同性混合物），无论使用哪种程序。最后，将设计的“核壳”纳米粒子掺杂 Eu(3+)，以证明非核壳结构也可以改善光学性能，与相应的核纳米粒子相比。这些结果表明，文献中关于通过 TEM 或增强发光推断获得核壳结构的结论可能不正确。
