Metal Hydrides as Novel Host Lattices for the Luminescence of Divalent Europium

掺杂到无机基质晶格中的二价Eu具有优异的发光性能，因此作为荧光粉的应用引起了人们的极大兴趣。氧化物、卤化物、磷酸盐和硅酸盐等化合物作为基质材料被广泛研究，其中Eu(II)通常表现为蓝色或绿色发光。最近，掺Eu(II)的氮化物显示出从黄色到橙色的发射。最近，我们首次研究了金属氢化物作为Eu(II)发光的主体晶格，并发现了红光发射，即在此类化合物中观察到的最大红移。我们将大红移归因于氢化物离子的极化率和明显的高配位场强度。此外，我们还在立方钙钛矿LiSrH3：Eu2+中发现了非常明亮的黄色发射。因此，金属氢化物似乎是一类有趣的化合物，是一种新型的主体材料。这个项目是关于进一步探索Eu(II)发光的潜力。特别是，为了了解发光强度、寿命或发光猝灭，必须研究主体晶格对Eu2+5d能级位置和分裂的影响。适合于Eu掺杂的基质包括钙钛矿型LiMH3(M=Sr，Ba，Sr1-yBay)、MMgH4(M=Sr，Ba)和KMgH3。这些材料将掺入不同量的Eu(0.1-2%)，并通过X射线衍射、中子衍射和发光光谱进行表征，包括很高的分辨率光谱、低温以及寿命和量子效率的测量。我们将进一步利用氢化物-氟化物的类比，尝试合成这些氢化物与类似的氟化物的固溶体，如LiMHnF3-n：Eu2+(M=Sr，Ba2+)或KMgHnF3-n：Eu2+。如果氢化物和氟化物的比例能够连续变化，我们应该能够在很大范围内调节Eu(II)掺杂的氢化物和氟化物的发射波长，因为氟化物的发射是蓝色或绿色，而氢化物的发射是黄色或红色的。此外，最近发展的合成方法将被用来重新研究已知的金属氢化物的晶体结构，例如我们现在可以制备单相的SrMgH4，并尝试制备新的主体晶格，如M(II)=Sr，Ba或SR1-yBayMgH4的KMgH3-M(II)MgH4体系。在制备和表征上述Eu掺杂金属氢化物的基础上，我们希望阐明这类新型主体晶格中Eu(II)发光的影响因素，并探索其作为发光材料的潜力。

Divalent europium doped into inorganic host lattices shows exceptional luminescence properties and is therefore of great interest for applications as a phosphor. Compounds such as oxides, halides, phosphates and silicates have been extensively studied as host material, in which Eu(II) usually shows blue or green emission. Eu(II) doped nitrides have more recently been shown to exhibit yellow to orange emission. Very recently we have investigated metal hydrides for the first time as host lattice for Eu(II) luminescence and found red emission, i. e. the largest redshift ever observed in such compounds. We attribute the large redshift to the polarizability and apparently high ligand field strength of the hydride ion. Further we found very bright yellow emission in the cubic perovskite LiSrH3:Eu2+. Metal hydrides seem therefore to be an interesting class of compounds as novel host materials. This project is about further exploring this potential for Eu(II) luminescence. In particular the influence of the host lattice on the position and splitting of the Eu2+ 5d levels shall be investigated in order to understand luminescence intensities, life times or luminescence quenching. Suitable hosts for europium doping include perovskites LiMH3 (M = Sr, Ba, Sr1-yBay), MMgH4 (M = Sr, Ba) and KMgH3. These materials will be doped with different amounts of europium (0.1-2%) and characterized by X-ray diffraction, neutron diffraction and luminescence spectroscopy, including very high resolution spectra, low temperature and measurements of lifetime and quantum efficiency. We will further take advantage of the hydride-fluoride analogy by trying to synthesize solid solutions of these hydrides with the analogous fluorides, such as LiMHnF3-n:Eu2+ (M = Sr, Ba) or KMgHnF3-n:Eu2+. If the hydride-fluoride ratio can be continuously varied, we should be able to tune the emission wavelength of the Eu(II) doped mixed hydride-fluoride over a wide range, because the fluorides show emission in the blue or green while hydrides show emission in the yellow or red. In addition recently developed synthesis methods will be used to reinvestigate the crystal structure of known metal hydrides, e. g. SrMgH4, which we can now prepare single phase, and to attempt preparation of new host lattices like in the systems KMgH3-M(II)MgH4 with M(II) = Sr, Ba or Sr1-yBayMgH4. On preparing and characterizing the above described europium doped metal hydrides we hope to elucidate the factors governing Eu(II) emission in this new class of host lattices and explore their potential as luminescent materials.