  Laser-induced fluorescence spectra and excitation lifetimes of anthracene,
tetracene, and pentacene molecules attached to the surface of solid argon
clusters have been measured with respect to cluster size, density of molecules
and excitation density. Results are compared to previous studies on the same
sample molecules attached to neon clusters. A contrasting lifetime behavior of
anthracene on neon and argon clusters is discussed, and mechanisms are
suggested to interpret the results. Although both neon and argon clusters are
considered to be weakly interacting environments, we find that the excitation
decay dynamics of the studied acenes depends significantly on the cluster
material. Moreover, we find even qualitative differences regarding the
dependence on the dopant density. Based on these observations, previous
assignments of collective radiative and non-radiative decay mechanisms are
discussed in the context of the new experimental findings.
