Electronic relaxation in lead clusters: An indicator of non-metallic behavior

Time-resolved photoemission spectroscopy was used to shed light on the relaxation dynamics of optically excited states of mass-selected Pbn cluster anions. For clusters with 9–21 atoms, relaxation times were estimated to be several picoseconds as expected for non-metallic species. For Pb12− and Pb13−, it was possible to observe photo-excited electrons hopping down the ladder of excited states back to the ground state. For Pb28−, a long relaxation time of 15 ps was found, i.e., although the density of states increased considerably with increasing cluster size, electronic relaxation was still very slow at this cluster size due to its non-metallic nature.