Congratulations to Dr. Mark Mangnus for an Excellent PhD Defense. Mark has successfully defended his PhD thesis, supervised by Prof. Bert Weckhuysen, prof. dr. Alfons van Blaaderen, and dr. Freddy Rabouw.

In his thesis, Mark studied lanthanide doped materials. These materials have well-defined emission energies that are barely affected by the host crystal in which the lanthanides are incorporated. The general belief is that, just like in bulk crystals, the emission properties of lanthanide ions in nanocrystals (NCs) are independent of their local environment. They challenged this viewpoint, first of all by showing that dopant-to-dopant energy transfer (ET) is hampered in NCs, which alters the photoluminescence output. They also investigated how a special type of ET—from dopant ions to molecular vibrations at the NC surface—quenches the luminescence from specific lanthanide levels. Importantly, once a lanthanide ion has acted as a donor for ET, it can no longer emit light (of the same color), and vice versa. In other words, ET and radiative decay are competing processes, and the PL output is determined by the relative efficiencies of radiative decay and ET.