Luminescence evidence for bulk and surface excitons in free xenon clusters

TL;DR

This study uses cathodoluminescence to investigate bulk and surface excitons in free xenon clusters, revealing how cluster composition affects excitonic emissions and discovering new luminescent bands.

Contribution

It provides new experimental evidence of excitonic phenomena in free xenon clusters and shows the impact of argon shells on luminescence.

Findings

Detection of bulk and surface excitons in xenon clusters

Argon shell causes extinction of excitonic bands

Discovery of new luminescent bands with no bulk analogs

Abstract

Cathodoluminescence spectra of free xenon clusters produced by condensation of xenon-argon gas mixtures in supersonic jets expanding into vacuum were studied. By varying initial experimental parameters, including 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 (about 1500 atoms). The cluster size and temperature (about 40 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. A presence of an argon shell causes extinction of the excitonic bands. In addition, some new bands were found which have no analogs for bulk xenon cryosamples.