Mixed Anionic Metal Hydrides as Host Lattices for the Luminescence of Divalent Europium

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Divalent europium, Eu(II), in inorganic host lattices is of great interest for applications in lighting devices. In oxide based compounds and in halogenides, it usually shows blue or green emission upon excitation with UV light (photoluminescence). With more polarizable ligands, such as nitrides or hydrides, the emission shifts to yellow, orange or red. By investigating mixed anionic hydridic host materials, we want to systematize the influence of dopant concentration, bond length, number of hydride ligands, mixing of hard and soft anions, coordination number and symmetry on luminescence properties. 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. Hydridic host materials will be from various classes of mainly ionic mixed anionic metal hydrides, e. g. perovskite-type hydride fluorides KCaH3-xFx (1 < x < 3), pyrochlore-type hydride fluorides and hydride oxides NaCaMg2F7-xHx, NaSrMg2F7-xHx, KCaNb2O6F1-xHx, and KCaTa2O6F1-xHx, hydride halogenides MHX (M = Ca, Sr, Ba; X = Cl, Br, I), lanthanide hydride oxides LnHO, and hydride silicates. Identifying and quantifying the crystal chemical key parameters for Eu(II) luminescence in such compounds will enable us to make predictions for the ideal chemical environment around europium atoms for a chosen emission wavelength, to suggest suitable crystal structures and thus the knowledge-driven development of luminescence materials. This will provide a deep understanding of Eu(II) luminescence in mixed-anionic metal hydrides at a level, where it can be used as a guide for the search of new luminescence materials.