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标题：Investigation on the structure and upconversion fluorescence of Yb³⁺/Ho³⁺ co-doped fluorapatite crystals for potential biomedical applications
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作者：Xiyu Li ; Jingxian Zhu ; Zhentao Man 等
期刊名称：Scientific Reports
电子版ISSN：2045-2322
出版年度：2014
卷号：4
DOI：10.1038/srep04446
出版社：Springer Nature
摘要：Rare-earth Yb³⁺ and Ho³⁺ co-doped fluorapatite (FA:Yb³⁺/Ho³⁺) crystals were prepared by hydrothermal synthesis, and their structure, upconversion properties, cell proliferation and imaging were investigated. The synthesized crystals, with a size of 16 by 286 nm, have a hexagonal crystal structure of classic FA and a Ca/Yb/Ho molar ratio of 100/16/2.1. Several reasonable Yb³⁺/Ho³⁺ -embedding lattice models along the fluorine channel of the FA crystal cell are proposed for the first time, such as models for (Ca₇YbHo©)(PO₄)₆F₂ and (Ca₆YbHoNa₂)(PO₄)₆F₂. The activated FA:Yb³⁺/Ho³⁺ crystals were found to exhibit distinct upconversion fluorescence. The 543- and 654-nm signals in the emission spectra could be assigned, respectively, to the ⁵F₄ (⁵S₂) - ⁵I₈ and ⁵F₅ - ⁵I₈ transitions of holmium via 980-nm near-infrared excitation and the energy transfer of ytterbium. After the surfaces were grafted with hydrophilic dextran, the crystals displayed clear fluorescent cell imaging. Thus, the prepared novel FA:Yb³⁺/Ho³⁺ upconversion fluorescent crystals have potential applications in the biomedical field.