Anion-hydride-exchange as a tool for material design - substitution effects in fluorides, fluoride borates and fluoride phosphates studied by local probes
Final Report Abstract
While metal hydrides have been studied due to their possible use as alternative energy storage for many years, during recent times especially mixed-anionic hydrides have come info the focus of attention. This is because of their various interesting chemical and physical properties, such as interesting electric and ionic conductions or magnetic properties. Especially a number of interesting new oxide hydrides have been prepared lately. However, there is a need to better understand material properties and many fields of possible mixedanionic hydrides remain unexplored. While X-ray and neutron diffraction delivers averaged structural information, it is helpful to use local probes for a deeper understanding, for instance of polarizabilities and chemical bonding. Ideally suited as local probes in materials with sufficiently large band gaps are rare earth metal ions. Their optical transitions react very sensitively towards the local environment. While the energetic position of 5d-4f- transitions depends strongly on the coordination sphere, 4f-4f-transitions often show narrow lines and are sensitive to the local symmetry. Additionally, also EPR and ENDOR spectroscopy may add to the information. Within the present project, we explored hydride substitution as a tool for material design, investigating different model systems, such a fluorides, fluoride borates and fluoride phosphates as well as the use of local probes for their understanding. In first model systems RbMgF3-xHx and MCaF3-xHx (M = Rb, Cs) Eu2+-doping was investigated. While in the first system, a smooth redshift of a broad emission band was observed, in the second case with M = Cs, a very interesting set of several narrow-band emissions appeared. This observation which may serve as a general model for colour tuning in such compounds. ENDOR spectroscopy on first Eu2+-doped hydride model systems was elucidated. In order to also have comparable host materials for trivalent RE ion doping at hand, double perovskites were screened for possible hydride fluorides. As a first preliminary result, a weak Tb3+ emission could be observed in Rb2KYF5.5H0.5:Tb3+. The exploration of new anion combinations lead to the first successful syntheses of a fully hydride-substituted phosphate as well as an unprecedented borate hydride. For the characterization of both new model classes, a number of independent methods were used to unambiguously prove the incorporation of hydride and the absence of hydroxide, including neutron powder diffraction of deuterated samples, 1H magic angle spinning solid-state NMR and vibrational spectroscopy together with quantum chemical calculations of the 1H chemical shifts and the vibrational spectra as well as elemental analysis. In case of the borate hydride, we succeeded in obtaining an interesting orange-red Eu2+ 5d-4f emission. Additionally, first studies of borohydrides as host lattices for sensitive optical thermometry were carried out using an interestingly large temperature-response of Eu2+ 4f65d1-4f7 transition the in such systems. In summary, the project contributed in successfully establishing knowledge on mixed-anionic hydrides as well as the use of rare earth ions as local probes in such materials.
Publications
- Lanthanide luminescence as a local probe in mixed anionic hydrides – A case study on Eu2+-doped RbMgHxF3-x and KMgHxF3-x, J. Mater. Chem. C 2018, 6, 13006-13012
Th. Wylezich, S. Welinski, M. Hölzel, Ph. Goldner, N. Kunkel
(See online at https://doi.org/10.1039/C8TC03881C) - An unprecedented fully H– – substituted phosphate hydride Sr5(PO4)3H expanding the apatite family, Eur. J. Inorg. Chem. 2019, 48, 5073-5076
A. Mutschke, Th. Wylezich, C. Ritter, A. J. Karttunen, N. Kunkel
(See online at https://doi.org/10.1002/ejic.201901151) - Lanthanide Ions as Local Probes in Ionic Hydrides: A Pulsed Electron Nuclear Double Resonance and Thermoluminescence Study of Eu2+-Doped Hydride Perovskites, J. Phys. Chem. C 2019, 123, 5031-5041
Th. Wylezich, R. Böttcher, A. Sontakke, V. Castaing, B. Viana, A. Pöppl, N. Kunkel
(See online at https://doi.org/10.1021/acs.jpcc.8b12420) - One ion, many facets: Efficient, structurally and thermally sensitive luminescence of Eu2+ in binary and ternary strontium borohydride chlorides, Chem. Mater. 2019, 31, 8957−8968
Th. Wylezich, A. D. Sontakke, V. Castaing, M. Suta, B. Viana, A. Meijerink, N. Kunkel
(See online at https://doi.org/10.1021/acs.chemmater.9b03048) - Borate hydrides as a new material class – Structure, computational studies and spectroscopic investigations on Sr5(BO3)3H and Sr5(11BO3)3D, Chem. Eur. J. 2020, 51, 11742-11750
Th. Wylezich, R. Valois, M. Suta, A. Mutschke, C. Ritter, A. Meijerink, A. J. Karttunen, N. Kunkel
(See online at https://doi.org/10.1002/chem.202002273) - ACaHxF3- x (A = Rb, Cs): Synthesis, structure and bright, site-sensitive tunable Eu2+ luminescence, Adv. Optical. Mater. 2021, 2002052
A. Mutschke, Th. Wylezich, A. D. Sontakke, M. Hoelzel, A. Meijerink, N. Kunkel
(See online at https://doi.org/10.1002/adom.202002052)
