Anion-hydride-exchange as a tool for material design - substitution effects in fluorides, fluoride borates and fluoride phosphates studied by local probes

氢化物部分取代阴离子用于材料设计近年来引起了人们的极大关注，尝试更好地定位材料中的少量氢化物阴离子起着重要的作用。结果表明，取代引起了材料性质的显著变化，例如电导率。这意味着氢化物的掺入显著地改变了材料的物理和化学性质。这种效应的本质目前还不完全清楚，但假设与氢化物阴离子的高极化率有关。尽管中子和X射线衍射法是描述氢化物的一个非常强大的工具，但除了平均结构数据之外的信息，例如关于共价和极化率的局域信息，为了获得更深层次的理解是必不可少的，例如当材料只被氢化物部分取代时。在这个项目的框架内，我们建议使用局域探针而不是衍射法。对于足够大的带隙，这是一种合适的方法，例如与稀土离子掺杂一起使用。4f-4f和5d-4f过渡都可以提供有关当地环境的信息。后者以其对极化率差异的敏感性而闻名，正如氮化物中Eu2+发射能量相对于氧化物或氟化物的红移所表明的那样。氮化物中常见的橙色或红色发光如今被用于固态照明应用。在纯氢化物中的初步工作强烈表明，在氢化物环境中也发生了类似的效应。在这里，我们的目标是探索氢化物替代作为材料设计的工具。作为取代氟离子与氢化物结合的模型体系，我们首先选择了纯氟化物，然后选择了氟化硼和氟磷酸盐。除了用X射线和中子衍射法进行结构表征外，我们还将特别研究稀土离子作为光学探针的作用。这些研究将通过使用电子顺磁共振光谱学和核磁共振光谱学加以补充。总而言之，该项目将有助于了解氢化物取代化合物的存在和化学，以及结构和光谱性质之间的关系。

Partial substitution of anions by hydride for materials design is recently attracting a lot of attention and attempts to better localize small amounts of hydride anions in materials play an important role. It was shown that the substitution induces significant changes in materials properties, for example in the conductivity., meaning that incorporation of hydride significantly modifies the physical and chemical properties of a material. The nature of this effect is not yet completely understood, but a relation with the high polarizability of the hydride anion is assumed. Even though neutron and X-ray diffraction methods are a very powerful tool to describe hydrides, information beyond the averages structural data, such as local information regarding covalence and polarizability are essential in order to gain a deeper understanding, for example when materials are only partially substituted by hydride.Within the frame of this project we are proposing the use of local probes besides diffraction methods. In relation with sufficiently large band gaps, these represent a suited method, for example together with rare earth ion doping. Both 4f-4f and 5d-4f transitions can deliver information on the local environment. The latter are known for their sensitivity towards differences in polarizabilities, as the example of the redshift of the Eu2+ emission energies in nitrides compared to oxides or fluorides has shown. The orange or red emission usually found in nitrides is nowadays commercially used in solid state lighting applications. First preliminary works in pure hydrides strongly suggest that a similar effect is taking place in a hydridic environment.Here, we are aiming at exploring hydride substitution as a tool for materials design. As model systems for the incorporation of hydride by substituting fluoride anions, first we have chosen pure fluorides, then fluoride borates and fluoride phosphates. Beside structural characterization by means of X-ray and neutron diffraction methods, we will especially investigate how rare earth ions can serve as optical probe. These studies will be supplemented by the use of electron paramagnetic resonance spectroscopy and nuclear magnetic resonance spectroscopy. In summary, the project will contribute to the knowledge on the existence and the chemistry of hydride substituted compounds and also on the correlation between structural and spectroscopic properties.