Photoemission from doped solid rare gases

In this paper we report the results of an experimental study of the photoelectric yield of doped solid rare gases in the extreme ultraviolet (hω=8-30 eV) spanning the range of impurity excitations, exciton states, and interband transitions. Results were obtained for Xe in Kr, Xe in Ar, Kr in Ar, and benzene in Ar, Kr, and Xe. For dilute atomic and molecular impurities in solid rare gases three intrinsic photoemission mechanisms are exhibited: (a) direct excitation from the impurity state above the impurity threshold, (b) electronic energy transfer from the host exciton states to the impurity states resulting in exciton induced impurity photoemission, and (c) direct photoemission from the host matrix at energies above the matrix threshold. The photoemission thresholds from impurity states via processes (a) or (b) result in detailed information regarding electron affinities of solid rare gases which are in good agreement with recent data for the pure solids. A detailed study of exciton induced photoemission was conducted on Xe/Ar mixtures. The energy dependent photoemission line shape at different film thicknesses and at different concentrations was analyzed in terms of a kinetic picture involving competition between energy transfer from "free" excitons and exciton trapping. A quantitative estimate of the diffusion length of Wannier excitons in solid Ar was extracted.