Transmission and Ellipsometric Spectroscopy of Impurities in Metals.

The excitation spectra of Mg, Cu, Ag, Sc, Cr, Mn, and Fe in alkali metal hosts are reported. Both optical transmission and differential ellipsometric spectroscopies were employed to obtain impurity spectra. Remarkably atomic -like excitation spectra are observed. In the case of Ag the excitation spectrum in the alkali metals has been investigated throughout the photon energy range 5 - 12 eV using optical transmission spectroscopy. Both orbital- and spin-dependent features of the atomic spectrum are preserved to an unexpected degree. The excitations observed are identified as arising from both 4d (--->) 5p and 5s (--->) 6p transitions. Ellipsometric measurements were used to extend the investigation over the photon energy range 1.3 - 4.5 eV. The impurity spectra were resolvable into four parts: single particle scattering, plasmon processes, local excitations, and the associated shakeoff processes. In each case the local excitation spectrum is fairly well described by a model based on the atomic excitation spectra red shifted and broadened in energy by interaction with the host metal. No lower-energy limit on the existence of such local effects has been identified. The conditions for the emergence of persistent spectra in metals are discussed in terms of host-impurity coupling.