镧系掺杂上转换纳米晶体的晶体结构及形成机理的探讨,Chemistry of Materials

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镧系掺杂上转换纳米晶体的晶体结构及形成机理的探讨
Chemistry of Materials ( IF 7.2 ) Pub Date : 2016-11-23 00:00:00 , DOI: 10.1021/acs.chemmater.6b04140
D. Hudry ₁ , A. M. M. Abeykoon ₂ , E. Dooryhee ₂ , D. Nykypanchuk ₃ , J. H. Dickerson _{1,

3}

Affiliation

掺杂镧系元素（Ln）的上转换纳米晶体（UCNC），例如NaLnF ₄（Ln =镧系元素），由于其将近红外光子转换为近紫外光或可见光的能力而构成了一类重要的纳米级材料。尽管经过十多年的深入研究，但UCNC的开发仍相对不足，尤其是在有机介质中其晶体结构和形成机理方面。前者需要解释原子尺度结构与UCNC的上转换（UC）特性之间的关系（即，4f–4f跃迁概率的局部对称，Ln ³⁺能量迁移距离），而后者对于微调定义明确的上转换纳米结构的尺寸，形态，化学组成和结构至关重要，这些结构构成了修改光学特性的实验手段。在这项贡献中，我们使用基于同步加速器的衍射实验以及Rietveld和成对分布函数（PDF）分析来了解NaGdF ₄：Yb：Er UCNC在有机介质中的形成并研究其晶体结构。我们的结果揭示了基于涉及分子簇和高温下原位生成的结晶氟化钠的化学反应，NaGdF ₄：Yb：Er UCNC形成的复杂机制。此外，对NaGdF ₄的详细晶体学研究：Yb：Er UCNC出现了。我们里特维尔德和PDF的分析表明，空间群P 6是一个最能说明NaGdF的晶体结构₄：镱铒UCNCs相反的是最近已提出。此外，我们的Rietveld和PDF数据揭示了低至10 nm的大块状晶体结构的形成，变形有限。本文介绍的结果构成了全面了解控制镧系元素掺杂纳米结构的UC特性的基础图的重要一步。

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Probing the Crystal Structure and Formation Mechanism of Lanthanide-Doped Upconverting Nanocrystals

Lanthanide (Ln)-doped upconverting nanocrystals (UCNCs), such as NaLnF₄ (with Ln = lanthanide), constitute an important class of nanoscale materials due to their capacity to convert near-infrared photons into near-ultraviolet or visible light. Although under intense investigation for more than a decade, UCNCs have been relatively underexplored especially regarding their crystal structure and mechanisms of formation in organic media. The former is needed to explain the relationship between atomic scale structure and upconversion (UC) properties of UCNCs (i.e., local symmetry for 4f–4f transition probability, Ln³⁺ distances for energy migration), while the latter is essential to finely tune the size, morphology, chemical composition, and architecture of well-defined upconverting nanostructures, which constitute the experimental levers to modify the optical properties. In this contribution, we use synchrotron-based diffraction experiments coupled to Rietveld and pair distribution function (PDF) analyses to understand the formation of NaGdF₄:Yb:Er UCNCs in organic media and to investigate their crystal structure. Our results reveal a complex mechanism of the formation of NaGdF₄:Yb:Er UCNCs based on chemical reactions involving molecular clusters and in situ-generated, crystalline sodium fluoride at high temperature. Additionally, a detailed crystallographic investigation of NaGdF₄:Yb:Er UCNCs is presented. Our Rietveld and PDF analyses show that the space group P6̅ is the one that best describes the crystal structure of NaGdF₄:Yb:Er UCNCs contrary to what has been recently proposed. Further, our Rietveld and PDF data reveal the formation of bulk-like crystal structure down to 10 nm with limited distortions. The results presented in this paper constitute an important step toward the comprehensive understanding of the underlying picture that governs UC properties of lanthanide-doped nanostructures.

更新日期：2016-11-23

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