  For the first time in binary mixtures of solid rare gases exciton-impurity
luminescence is observed from a xenon-argon system containing argon as
impurity. An exciton-impurity emission band is registered for binary clusters
with the structure of multilayer icosahedron. The optical transition occurs
from an energy level lying very close to the lowest level of volume excitons in
bulk xenon samples. The results demonstrate the possibility of probing
excitonic levels in noncrystalline condensed media.
