Luminescence evidence for bulk and surface excitons in free xenon clusters

Abstract

The cathodoluminescence spectra of free xenon clusters produced by condensation of xenon-argon gas mixtures in supersonic jets expanding into vacuum were studied. By varying the initial experimental parameters, including the xenon concentration, we could obtain clusters with a xenon core (300--3500 atoms) covered by an argon outer shell as well as shell-free xenon clusters ($\ensuremath{\approx}1500$ atoms). The cluster size and temperature ($\ensuremath{\approx}40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for both cases) were measured electronographically. Luminescence bands evidencing the existence of bulk and surface excitons were detected for shell-free xenon clusters. The emission from bulk excitons in small clusters is supposed to be due to processes of their multiple elastic reflections from the xenon-vacuum interface. The presence of an argon shell causes extinction of the excitonic bands. In addition, some bands were found which have no analogs for bulk xenon cryosamples.