Comprehensive study of the luminescence properties of elemental metals

The lifetime and intensity of ultrafast luminescence in the near-infrared region were investigated for 15 representative elemental metals: simple light metals (Be, Mg, and Al); $3d$ (Ti, Ni, and Zn), $4d$ (Zr, Mo, Pd, and Sn), and $5d$ (W and Pt) transition metals; and noble metals (Au, Ag, and Cu). The luminescence intensity at 0.9 eV was distributed over a range as wide as 2.5 orders of magnitude. The sum of an instantaneous response and an exponential decay component well approximated the time-evolution of the luminescence intensity at 0.6 eV. The lifetimes obtained from this decomposition were distributed in a narrower range from 110 fs (Be) to 694 fs (Ag), corresponding to a factor 6.3. We proposed a model based on the dielectric function of the bulk metal to understand the luminescence intensity of the quasi-instantaneous component. It was found that the luminescence intensity was inversely proportional to the Drude damping constant, that is, the slower the damping, the stronger the luminescence. This shows that quasi-instantaneous luminescence is quenched by the nonradiative decay of the nonthermal electrons via electron-electron scattering. The electron-phonon (e-ph) coupling strengths were evaluated using Eliashberg functions derived from ab initio calculations, and the decay rates corresponding to e-ph scattering were evaluated using the extended two-temperature model considering the equilibration process of excited electrons. We found fairly good agreement between the experimental and theoretical results for the absolute values of the exponential decay rates.