27.03.2025 Two masters in one day

We congratulate Johannes Röder and Felix Thomas, who both successfully defended their master’s theses today!

Johannes investigated the absorption of so-called type-II quantum well structures. These systems are interesting for applications as infrared emitters, but the properties of so-called charge transfer excitons, which are formed across the heterointerface after photoexcitation, are not yet well explored. Johannes studied different quantum well structures with charge transfer excitons at low temperatures in strong magnetic fields up to 7 Tesla. Under these conditions he could, for the first time, explore the magnetic properties of charge transfer excitons, such as Landau quantization and Zeeman splitting. His results showed excellent agreement with a microscopic theory developed in the group of Prof. Torsten Meier (U. Paderborn). The theoretical and experimental results were recently published in collaboration with AG Koch, AG Heimbrodt, AG Meier and AG Stolz (Physical Review B 110, 195306, 2024).

Felix focused on an entirely new class of light emitters. These materials are cluster compounds, comprised of an inorganic core with an adamantane-like structure and four organic ligands. Some of these compounds show white light emission in a highly nonlinear process, when they are driven by an infrared continuous wave laser source. This finding is of broader technological interest, because it allows for the generation of white light continua without the need of strong pulsed laser sources in a laboratory environment. After modifying two experimental setups for PL and PLE spectroscopy, Felix characterized a set of new cluster materials synthesized in the group of Prof. Stefanie Dehnen (Karlsruhe Institute of Technology), where one of the organic ligands was a bulky fluorescent molecule. Interestingly, Felix found that by changing from above- to sub-gap excitation, the emission of the material could be tuned from blue fluorescence to warm-white continuum emission. 

To both of you: Great job, thanks for the cake and all the best for the future!