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

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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.