82 research outputs found
Conduction band tuning by controlled alloying of Fe into Cs2AgBiBr6 double perovskite powders
Halide double perovskite semiconductors such as Cs2AgBiBr6 are widely
investigated as a more stable, less toxic alternative to lead-halide
perovskites in light conversion applications including photovoltaics and
photoredox catalysis. However, the relatively large and indirect bandgap of
Cs2AgBiBr6 limits efficient sunlight absorption. Here, we show that controlled
replacement of Bi3+ with Fe3+ via mechanochemical synthesis results in a
remarkable tunable absorption onset between 2.1 and ~1 eV. Our first-principles
density functional theory (DFT) calculations suggest that this bandgap
reduction originates primarily from a lowering of the conduction band upon
introduction of Fe3+. Furthermore, we find that the tunability of the
conduction band energy is reflected in the photoredox activity of these
semiconductors. Finally, our DFT calculations predict a direct bandgap when
>50% of Bi3+ is replaced with Fe3+. Our findings open new avenues for enhancing
the sunlight absorption of double perovskite semiconductors and for harnessing
their full potential in sustainable energy applications
Bifunctional Europium for Operando Catalyst Thermometry in an Exothermic Chemical Reaction
Often the reactor or the reaction medium temperature is reported in the field of heterogeneous catalysis, even though it could vary significantly from the reactive catalyst temperature. The influence of the catalyst temperature on the catalytic performance and vice versa is therefore not always accurately known. We here apply EuOCl as both solid catalyst and thermometer, allowing for operando temperature determination. The interplay between reaction conditions and the catalyst temperature dynamics is studied. A maximum temperature difference between the catalyst and oven of +16 °C was observed due to the exothermicity of the methane oxychlorination reaction. Heat dissipation by radiation appears dominating compared to convection in this set-up, explaining the observed uniform catalyst bed temperature. Application of operando catalyst thermometry could provide a deeper mechanistic understanding of catalyst performances and allow for safer process operation in chemical industries
E0 Transitions and the Depopulation of SD Bands
We present the results of calculations showing that E0 transitions may successfully compete with other types of electromagnetic transitions in the decay out of SD bands
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