Spectroscopy of PTCDA attached to rare gas samples: clusters vs. bulk   matrices. II. Fluorescence emission spectroscopy
  The interaction between PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) molecules and solid rare gas samples is studied by means of fluorescence emission spectroscopy. On the one hand, laser-excited PTCDA-doped large argon, neon and para-hydrogen clusters in comparison with PTCDA embedded in helium nanodroplets are spectroscopically characterized with respect to line broadening and shifting. A fast non-radiative relaxation is observed before a radiative decay in the electronic ground state takes place. On the other hand, fluorescence emission studies of PTCDA embedded in bulk neon and argon matrices results in much more complex spectral signatures characterized by a splitting of the different emission lines. These can be assigned to the appearance of site isomers of the surrounding matrix lattice structure. 
M. Dvorak, M. M\"uller, T. Knoblauch, O. B\"unermann, A. Rydlo, S.   Minniberger, W. Harbich and F. Stienkemeier
physics.atm-clus