Effect of Alkali-Metal Ions on the Local Structure and Luminescence for Double Tungstate Compounds AEu(WO4)2 (A = Li, Na, K)
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- 作者：Jinping Huang ; Jun Xu ; Hongshan Luo ; Xibin Yu ; Yikang Li
- 刊名：Inorganic Chemistry
- 出版年：2011
- 出版时间：November 21, 2011
- 年：2011
- 卷：50
- 期：22
- 页码：11487-11492
- 全文大小：331K
- 年卷期：v.50,no.22(November 21, 2011)
- ISSN：1520-510X
文摘
The effect of alkali-metal ions on the local structure and luminescence properties for alkali-metal europium double tungstate compounds AEu(WO4)2 (A = Li, Na, K) has been investigated by a dual-space structural technique, atomic pair distribution function (PDF) analysis, and the Rietveld method of powder X-ray diffraction. The compounds AEu(WO4)2 (A = Li, Na) crystallize in the isostructure with the tetragonal space group I41/a (No. 88) and show the same luminescence properties in spite of the different doped alkali metals. However, KEu(WO4)2 crystallizes in monoclinic symmetry with the space group C2/c (No. 15). Compared with the two other counterparts, KEu(WO4)2 exhibits a more effective charge-transfer excitation, a larger Stokes shift, and a broader 612 nm emission band. This phenomenon is ascribed to the lower crystal symmetry in KEu(WO4)2, which influences bond distances and the coordination number of Eu3+. Two complementary methods, the Rietveld method and PDF analysis, reveal that both LiEu(WO4)2 and NaEu(WO4)2 afford the same local surroundings of Eu3+. The local structure determined by the Rietveld and PDF methods well account for the observed luminescent properties.