Observation of nanostructured cluster formation of Tm ions in CaF₂ crystals

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• 作者：G. Drae ; ić ; S. Kobe ; A.C. Cefalas ; E. Sarantopoulou ; Z. Kollia
• 关键词：Solid– ; liquid interface ; Density fluctuations ; Phase transitions ; Clusters ; Transmission electron microscopy ; Nanocrystals
• 刊名：Materials Science and Engineering: B
• 出版年：2008
• 出版时间：25 August 2008
• 年：2008
• 卷：152
• 期：1-3
• 页码：119-124
• 全文大小：826 K

文摘

Transmission electron microscopy, energy dispersive X-ray spectroscopy, and high-resolution scanning-transmission electron microscopy, with electron beam sizes ranging from 2 to 50 nm, were used to investigate the spatial distribution and homogeneity of doped Tm³⁺ ions in CaF₂ host matrices with atomic resolution, in solid crystals grown from melts using the Bridgman–Stockbarger method. With the smallest size electron beam available of 2 nm, it was found that the Tm³⁺ ions were distributed inhomogeneously at the host sites. They took the form of sub-nm agglomerations of 3–5 atoms, rather than individual ions and the phase transition layer was 0.1 nm thick. The spatial extend of inhomogeneous Tm³⁺ concentration was 2.6–6 nm and originates from ionic density fluctuations in the liquid phase at the interface layer due to the local electrostatic field at the ionic sites.