Direct Evidence of Significant Cation Intermixing in Upconverting [email protected] Nanocrystals: Toward a New Crystallochemical Model,Chemistry of Materials

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Direct Evidence of Significant Cation Intermixing in Upconverting [email protected] Nanocrystals: Toward a New Crystallochemical Model
Chemistry of Materials ( IF 7.2 ) Pub Date : 2017-11-02 00:00:00 , DOI: 10.1021/acs.chemmater.7b03118
Damien Hudry ₁ , Dmitry Busko ₁ , Radian Popescu ₂ , Dagmar Gerthsen ₂ , A. M. Milinda Abeykoon ₃ , Christian Kübel ₄ , Thomas Bergfeldt ₅ , Bryce Sydney Richards _{1,

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Affiliation

[email protected] design represents an important class of architectures because of its capability not only to dramatically increase the absolute upconversion quantum yield (UCQY) of upconverting nanocrystals (UCNCs) but also to tune energy migration pathways. A relatively new trend toward the use of very thick optically inert shells affording significantly higher absolute UCQYs raises the question of the crystallographic and chemical characteristics of such nanocrystals (NCs). In this article, local chemical analyses performed by scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy (EDXS) and X-ray total scattering experiments together with pair distribution function (PDF) analyses were used to probe the local chemical and structural characteristics of hexagonal β-NaGd_0.78Yb_0.2Er_0.02F₄@NaYF₄ [email protected] UCNCs. The investigations lead to a new crystallochemical model to describe [email protected] UCNCs that considerably digresses from the commonly accepted epitaxial growth concept with sharp interfaces. The results obtained on ultrasmall (4.8 ± 0.5 nm) optically active cores (β-NaGd_0.78Yb_0.2Er_0.02F₄) surrounded by an optically inert shell (NaYF₄) of tunable thickness (roughly 0, 1, 2, and 3.5 nm) clearly indicate the massive dissolution of the starting seeds and the interdiffusion of the shell element (such as Y) into the Gd/Yb/Er-containing core giving rise to the formation of a nonhomogeneous solid solution characterized by concentration gradients and the lack of sharp interfaces. Independently of the inert shell thickness, core/interface/shell architectures were observed for all synthesized UCNCs. The presented results constitute a significant step toward the comprehensive understanding of the “structure–property” relationship of upconverting [email protected] architectures, which is of prime interest not only in the development of more efficient structures but also to provide new physical insights at the nanoscale to better explain upconversion (UC) properties alterations.

中文翻译：

在上转换[受电子邮件保护的]纳米晶体中大量阳离子混入的直接证据：建立新的晶体化学模型

受电子邮件保护的设计代表了一类重要的体系结构，因为它不仅具有显着提高上转换纳米晶体（UCNC）的绝对上转换量子产率（UCQY）的能力，而且还具有调节能量迁移路径的能力。使用非常厚的光学惰性壳以提供明显更高的绝对UCQY的相对较新的趋势提出了这种纳米晶体（NC）的晶体学和化学特性的问题。在本文中，通过扫描透射电子显微镜（STEM）结合能量色散X射线光谱（EDXS）进行的局部化学分析和X射线总散射实验以及对分布函数（PDF）分析被用于探测局部化学物质。和六边形的结构特征β-NaGd _0.78Yb _0.2 Er _0.02 F ₄ @NaYF ₄ [受电子邮件保护] UCNC。研究导致了一种新的晶体化学模型来描述[受电子邮件保护的] UCNC，它与公认的具有尖锐界面的外延生长概念大相径庭。上超小（4.8±0.5 nm）的光学活性的核心获得的结果（β-NaGd _0.78镱_0.2铒_0.02 ˚F ₄）通过包围光学惰性壳（NaYF ₄）的可调厚度（大约0、1、2和3.5 nm）清楚地表明起始晶种的大量溶解以及壳元素（例如Y）向含Gd / Yb / Er的核中的相互扩散非均质固溶体的形成，其特征在于浓度梯度和缺乏尖锐的界面。独立于惰性壳厚度，对于所有合成的UCNC，观察到核/界面/壳结构。提出的结果构成了全面理解上转换[受电子邮件保护的]架构的“结构-属性”关系的重要一步，这不仅对于开发更高效的结构而且在提供新的物理见解方面都具有重大意义。纳米级可以更好地解释上转换（UC）属性的变化。

更新日期：2017-11-02

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