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

用氢化物部分取代阴离子用于材料设计最近引起了很多关注，并且试图更好地定位材料中的少量氢化物阴离子起着重要作用。结果表明，取代引起材料性质的显著变化，例如电导率。这意味着氢化物的引入显著地改变了材料的物理和化学性质。这种效应的性质尚未完全理解，但假设与氢化物阴离子的高极化率有关。 尽管中子和X射线衍射方法是描述质子的非常有力的工具，但是为了获得更深入的理解，例如当材料仅部分被氢化物取代时，除了平均结构数据之外的信息，例如关于共价性和极化率的局部信息是必不可少的。在本项目的框架内，我们建议使用衍射方法之外的局部探针。关于足够大的带隙，这些代表了合适的方法，例如与稀土离子掺杂一起。4f-4f和5d-4f转换都可以提供有关本地环境的信息。后者以其对极化率差异的敏感性而闻名，例如与氧化物或氟化物相比，氮化物中Eu 2+发射能量的红移。通常在氮化物中发现的橙子或红色发射现在商业上用于固态照明应用中。首先，在纯氢化物中的初步工作强烈地表明，类似的效应也发生在氢化物环境中。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。作为通过取代氟阴离子来结合氢化物的模型系统，首先我们选择了纯氟化物，然后是氟硼酸盐和氟磷酸盐。除了用X射线和中子衍射方法进行结构表征外，我们还将特别研究稀土离子如何作为光学探针。这些研究将补充使用电子顺磁共振光谱和核磁共振光谱。总之，该项目将有助于了解氢化物取代化合物的存在和化学性质，以及结构和光谱性质之间的相关性。

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.