Structure transformation and remarkable site-distribution modulation of Eu3+ ions in CaMoO4 : Eu3+ nanocrystals under high pressure
Structure transformation and remarkable site-distribution modulation of Eu3+ ions in CaMoO4 : Eu3+ nanocrystals under high pressure
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DOI：
10.1039/c5ce01580d
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发表时间：
2015-10
期刊：
影响因子：
3.1
通讯作者：
Zhi Zhao;Zhilei Sui;Xiantao Wei;Jian Zuo;Xianwen Zhang;R. Dai;Zengming Zhang;Zejun Ding
中科院分区：
文献类型：
--
作者：
Zhi Zhao;Zhilei Sui;Xiantao Wei;Jian Zuo;Xianwen Zhang;R. Dai;Zengming Zhang;Zejun Ding
利用拉曼光谱和发光光谱研究了平均尺寸为30 nm的白钨矿型CaMoO4: Eu3+纳米晶体在金刚石砧细胞（DAC）中高达21 GPa压力下的高压行为。在压力作用下，外部T（Bg）模式在10.8 GPa前的软化和新的拉曼峰的出现表明，在压力作用下，白钨矿结构向褐钨矿结构转变。当压力释放后，由于白钨矿和褐钨矿结构之间的结合强度差异很小，白钨矿相恢复。由于不同尺寸的CaMoO4: Eu3+样品的表面能存在差异，使得CaMoO4: Eu3+在纳米尺寸下的转化压力比块状样品略有提高。此外，通过位置选择性激发、发射和寿命谱，确定了在环境压力下CaMoO4: Eu3+纳米晶体中的Eu3+离子占据了体位和表面位。作为有效的位点探针，Eu3+离子的红-橙发光强度比I(5D0→7F2)/I（5D0→7F1）随压力变化显著，表明Eu3+离子的分布和局部对称性发生了较大变化。
High-pressure behaviors of scheelite-type CaMoO4 : Eu3+ nanocrystals with an average size of 30 nm have been investigated by using Raman and luminescence spectroscopy at pressures of up to 21 GPa in a diamond anvil cell (DAC). Under the loading of pressure, the softening of the external T(Bg) mode before 10.8 GPa and the appearance of new Raman peaks suggest a phase transformation around this pressure from scheelite to fergusonite structure. When the pressure is released, the scheelite phase recovers due to the small difference in bond strength between scheelite and fergusonite structures. The transformation pressure is slightly enhanced in nanosized CaMoO4 : Eu3+ as compared to the bulk due to the difference in surface energy between the two samples of different sizes. Moreover, it is identified that the Eu3+ ions occupy both the bulk and the surface sites in CaMoO4 : Eu3+ nanocrystals at ambient pressure by the site-selective excitation, emission and lifetime spectra. As an effective site probe, the red-to-orange luminescence intensity ratio of Eu3+ ions, I(5D0 → 7F2)/I(5D0 → 7F1), is found to exhibit remarkable changes with pressure, which indicates a large variation of the distribution and the local symmetry of Eu3+ ions.