Relaxation dynamics of hot electrons in the transition metals Au, Ag, Cu, Pt, Pd, and Ni studied by ultrafast luminescence spectroscopy

The ultrafast relaxation dynamics of photoexcited electrons in six transition metals, Au, Ag, Cu, Pt, Pd, and Ni, were investigated using femtosecond luminescence spectroscopy in the infrared region between 0.4 and 1.05 eV. The behaviors of the time-resolved spectra are significantly different between group 11 noble metals (Au, Ag, and Cu) and group 10 transition metals (Pt, Pd, and Ni), which are neighbors in the periodic table of elements. In the latter group, the instantaneous luminescence intensities are one order of magnitude lower and the lifetimes (around 200 fs) are far shorter than those of the group 11 metals (typically 700 fs). The time-resolved spectra, decay profiles, and excitation power dependence were analyzed using a phenomenological model that considers both the nonthermal and thermal electrons. It was found that the nonthermal component is remarkably small in the group 10 transition metals. These systematic differences between group 10 and 11 metals are ascribed to the differences in their electron band structures and/or electron-phonon coupling strengths.