Due to their optical and magnetic properties, rare earth ions are of great interest [1]. Doped into inorganic materials they are not only used for applications such as LEDs, laser and fibers, but they can also serve as local probes, because their optical transitions react very sensitively towards the local chemical environment. 5d-4f transitions usually show broad bands whose position strongly depends on the coordination sphere [2], for instance on the number and polarizability of the anions. The reason is the fact that the 5d levels are not well-shielded. In contrast, the 4f-4f transitions can exhibit extraordinarily narrow inhomogeneous and homogeneous line widths. The exact determination of those line widths can deliver important information on the properties of a material [3, 4].
Here, we use rare earth ions in polycrystalline materials for quantum information technologies as well as to study novel mixed-anionic and complex hydrides [e.g. 5, 6]. For instance, in borohydrides, we do not only find high quantum efficiencies, but also significant temperature-dependent shifts of the emission maxima [5]. The observed thermally induced blueshifts are in the order of 1000 to 1500 cm-1 which is, to the best of our knowledge, significantly larger than thermal shifts reported for Eu2+ d-f emission before and may also be promising for optical thermometry.
Furthermore, we investigate the existence of new anion combinations and found, among others, an unprecedented borate hydride showing orange-red emission when doped with Eu2+ and a novel sulphate hydride [7,8]. Besides, the use of hydrogenation reaction as material design tool for improved semiconductor materials is discussed.
Beamtime at the SPODI, Research Neutron Source Heinz Maier-Leibnitz (FRM II) and the D2b, Institute Laue-Langevin is gratefully acknowledged.
BiographieNathalie Kunkel studied chemistry at the Saarland University and obtained her diploma in 2010. After completing her PhD in 2014 with Prof. Dr. Holger Kohlmann and a short postdoctoral stay at Leipzig University, she moved to Philippe Goldner’s group at the IRCP in Paris (Materials for Photonics and Opto-Electronics) as a postdoctoral fellow of the CNRS and the DFG. In October 2016, she established a junior research group at the Technical University of Munich, Chemistry Department, supported by a Liebig fellowship of the Fonds der Chemischen Industrie and became a TUM Junior Fellow. Since 2019 she is a junior professor at the University of Göttingen where she is working on solid state materials, mainly with the focus on optical properties or energy applications and hydrogen storage. At the same time, she is also guest professor at the TU Munich, where she is a PI in the Graduate School ATMS (University of Alberta – Technical University of Munich) and where she also completed her habilitation in February 2021