TEMPERATURE-DEPENDENT LINE BROADENING OF CHROMOPHORES IN AMORPHOUS SOLIDS - DIFFERENCES BETWEEN SINGLE-MOLECULE SPECTROSCOPY AND PHOTON-ECHO RESULTS

Spectroscopic techniques exhibit different sensitivities for line broa dening processes in amorphous solids. Photon echo and hole-burning spe ctroscopy yield averages over the chromophore ensemble. At low tempera tures, the results can usually be fitted with a combination of a power -law term - corresponding to the relaxations of two-level systems - an d of an exponentially activated contribution of pseudo-local phonon mo des. Single-molecule spectroscopy (SMS), in contrast, can resolve the behavior of single dye molecules and yields a distribution of power la ws as well as of activation energies. We compare photon echo results f or tetra-tert-butylterrylene (TBT) in polyisobutylene (PIB) with SMS d ata for the same system. The latter were used to simulate numerically the data which would be obtained in an ensemble-averaging experiment. The results of the numerical calculation can be well fitted without as suming a distribution of parameters. (C) 1998 Elsevier Science B.V. Al l rights reserved.