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首页> 外文期刊>The Journal of Chemical Physics >5f- 5f transitions of U~(~(4+))ions in high-field,octahedral fluoride coordination:The Cs_2GeF_6:U~(4+)crystal
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5f- 5f transitions of U~(~(4+))ions in high-field,octahedral fluoride coordination:The Cs_2GeF_6:U~(4+)crystal

机译：U〜（〜（4+））离子在高场八面体氟化物配位中的5f-> 5f跃迁：Cs_2GeF_6：U〜（4+）晶体

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The U-F bond length,totally symmetric vibrational frequency,and 5f~2 energy levels of the Cs_2GeF_6:U~(4+)crystal are predicted through quantum-chemical calculations on the embedded(UF_6)~(2-)cluster.The U~(4+)ions substitute for much smaller Ge~(4+)retaining octahedral site symmetry,which is useful to interpret the electronic transitions.The structure of the 5f~2 manifold:its energy range,the crystal splitting of the 5f~2 levels,their parentage with free-ion levels,and the energy gaps appearing within the manifold,is presented and discussed,which allows to suggest which are the possible 5f~2 luminescent levels.The effects of Cl-to-F chemical substitution are discussed by comparison with isostructural Cs_2ZrCl_6:U~(4+).The energy range of the 5f~2 manifold increases by some 6000 cm~(-1)and all levels shift to higher energies,but the shift is not uniform,so that noticeable changes of order are observed from Cs_2ZrCl_6:U~(4+)to Cs_2GeF_6:U~(4+).The comparison also reveals that the green-to-blue up-conversion luminescence,which has been experimentally detected and theoretically discussed on Cs_2ZrCl_6:U~(4+),is quenched in the fluoride host.The results of the Cs_2GeF_6:U~(4+)are used as a high-symmetry model to try to understand why efficient radiative cascade emissions in the visible do not occur for charged U~(4+)defects in low-symmetry YF_3 crystals.The results presented here suggest that theoretical and experimental investigations of 4f/5f ions doped in octahedral,high-symmetry fluoride crystals may be conducted even when the mismatch of ionic radii between the lanthanide/actinide ions and the substituted cations of the host is considerably large.Investigations of these new materials should reveal interesting spectroscopic features without the difficulties associated with more commonly used low-symmetry fluoride hosts.
机译：通过对嵌入的（UF_6）〜（2-）团簇进行量子化学计算，预测Cs_2GeF_6：U〜（4+）晶体的UF键长度，完全对称的振动频率和5f〜2能级。 （4+）离子替代了较小的Ge〜（4+）保留八面体对称性，这对解释电子跃迁很有用。5f〜2流形的结构：其能级，5f〜2的晶体分裂给出并讨论了它们的能级，其与游离离子能级的亲缘关系以及在歧管内出现的能隙，从而可以提示可能的5f〜2发光级。与同构的Cs_2ZrCl_6：U〜（4+）比较。5f〜2流形的能量范围增加了约6000 cm〜（-1），所有能级都转移到了更高的能量，但这种转移并不均匀，因此很明显从Cs_2ZrCl_6：U〜（4+）到Cs_2GeF_6：U〜（4+）观察到了有序的变化。对Cs_2ZrCl_6：U〜（4+）进行了实验检测并在理论上进行了讨论，然后在氟化物主体中猝灭了变蓝的上转换发光。将Cs_2GeF_6：U〜（4+）的结果用作-对称模型以试图理解为什么低对称YF_3晶体中的带电U〜（4+）缺陷在可见光下不会发生有效的辐射级联发射。此处给出的结果表明，对4f / 5f离子进行了掺杂的理论和实验研究在八面体中，即使镧系元素/ act系元素离子与主体的取代阳离子之间的离子半径失配非常大，也可以进行高对称氟化物晶体的研究。这些新材料的研究应揭示出有趣的光谱特征，而不会带来任何困难更常用的低对称氟化物宿主。

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