Phys. Rev. Research 3, 033225 (2021)
Unravelling the electronic nature of the radiative cooling of cobalt clusters
Kristien Peeters1, Ewald Janssens1, Klavs Hansen1,2, Peter Lievens1, and Piero Ferrari1,*
1 Quantum Solid-State Physics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200d box 2414, 3001 Leuven, Belgium
2 Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, 92 Weijin Road, Tianjin 300072, China
In this paper, we report on the experimental determination of photon emission rates of laser-excited cobalt clusters, Con+ (n = 5–23), deduced from fragmentation mass spectrometry and metastable decay fractions. The rates are so high that they can only be ascribed to recurrent fluorescence (RF), a process where emitting states are populated by inverse internal conversion, followed by photon emission. Cooling via electronic states is confirmed by quantitative agreement with calculated rates using the low-lying electronic transitions predicted by time-dependent density functional theory calculations for n = 5–10, which are performed considering all electrons and including relativistic effects implicitly. The outstanding agreement between experiment and theory provides clear evidence that the clusters radiate via electronic states, being a consistent theoretical and experimental study invoking RF.