CONTINUOUS SECONDARY LIGHT-EMISSION FROM SILVER FILMS - ON THE ORIGIN OF THE INELASTIC BACKGROUND IN SERS

When cryocondensed silver films at 40 K are excited by laser photons in the optical energy range, a broad distribution of secondary photons with an energy shift from 250 cm-1 to beyond 3500 cm-1 is emitted. Upon annealing to 250 K we observe a narrowing of the emission band accompanied by an order of magnitude increase of the peak emission intensity. The emission is quenched by oxygen exposure. The data are explained by a second order light scattering process involving surface state intraband excitations. Tentatively, the excitation band is assigned to the intrinsic surface state at (111) facets.