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是近年来备受关注的研究方向，而尝试将少量的氢化物阴离子更好地定位在材料中起着重要的作用。结果表明，取代引起了材料性能的显著变化，例如电导率的变化。这意味着氢化物的加入会显著改变材料的物理和化学性质。这种效应的性质尚不完全清楚，但假定它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氢化物的一个非常强大的工具，但是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部信息，对于获得更深入的理解是必不可少的，例如当材料仅部分被氢化物取代时。在这个项目的框架内，除了衍射方法外，我们还建议使用局部探针。与足够大的带隙有关，这些代表了一种合适的方法，例如与稀土离子掺杂一起。4f-4f和5d-4f转换都可以传递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，如氮化物中Eu2+发射能量与氧化物或氟化物相比红移的例子所示。通常在氮化物中发现的橙色或红色发射物如今已在固态照明应用中商业化使用。最初对纯氢化物的初步研究强烈表明，在氢化物环境中也发生了类似的作用。在这里，我们的目标是探索氢化物取代作为材料设计的工具。作为取代氟阴离子的氢化物掺入的模型体系，我们首先选择了纯氟化物，然后是氟硼酸盐和氟磷酸盐。除了利用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。这些研究将辅以电子顺磁共振波谱和核磁共振波谱的使用。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.