Flux Crystal Growth, Crystal Structure, and Optical Properties of New Germanate Garnet Ce2CaMg2Ge3O12
Flux Crystal Growth, Crystal Structure, and Optical Properties of New Germanate Garnet Ce2CaMg2Ge3O12
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DOI：
10.3389/fchem.2020.00091
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发表时间：
2020-02
影响因子：
5.5
通讯作者：
Jie Chen;Hong Yan;A. Kuwabara;Mark D. Smith;Y. Iwasa;H. Ogino;Y. Matsushita;Y. Tsujimoto;K. Yamaura;H. zur Loye
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文献类型：
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作者：
Jie Chen;Hong Yan;A. Kuwabara;Mark D. Smith;Y. Iwasa;H. Ogino;Y. Matsushita;Y. Tsujimoto;K. Yamaura;H. zur Loye
通过熔剂晶体生长合成了一种新的锗酸盐石榴石化合物 Ce2CaMg2Ge3O12。从 BaCl2-CaCl2 熔体中生长出截头球形、红橙色单晶，典型尺寸为 0.1–0.3 毫米。通过单晶X射线衍射分析对单晶进行了表征，结果表明其采用立方石榴石型结构，空间群为Ia−3d，a = 12.5487(3) Å。其成分最好描述为 A3B2C3O12，其中 Ce/Ca、Mg 和 Ge 分别占据 A、B 和 C 位。对锗酸盐石榴石的紫外可见吸收光谱测量显示出对应于 2.21 eV（λ = 561 nm）带隙的清晰吸收边。第一性原理计算表明，价带最大值由Ce 4f 能带组成，而导带最小值主要由Ce 5d 能带组成。这些发现解释了通过 Ce 4f → 5d 吸收观察到的吸收边缘。光致发光发射光谱呈现出以 600 nm 为中心的非常宽的峰，对应于从最低能量 d 能级到 4f 能级的跃迁。
A new germanate garnet compound, Ce2CaMg2Ge3O12, was synthesized via flux crystal growth. Truncated spherical, reddish-orange single crystals with a typical size of 0.1–0.3 mm were grown out of a BaCl2-CaCl2 melt. The single crystals were characterized by single-crystal X-ray diffraction analysis, which revealed that it adopted a cubic garnet-type structure with a = 12.5487(3) Å in the space group Ia−3d. Its composition is best described as A3B2C3O12, where Ce/Ca, Mg, and Ge occupied the A, B, and C sites, respectively. A UV–vis absorption spectroscopy measurement on the germanate garnet revealed a clear absorption edge corresponding to a band gap of 2.21 eV (λ = 561 nm). First-principle calculations indicated that the valence band maximum was composed of Ce 4f bands, whereas the conduction band minimum mainly consisted of Ce 5d bands. These findings explain the observed absorption edge through the Ce 4f → 5d absorption. Photoluminescence emission spectra exhibited a very broad peak centered at 600 nm, corresponding to transition from the lowest energy d level to the 4f levels.