COMPARISON OF PHOTON-ECHO, HOLE-BURNING, AND SINGLE-MOLECULE SPECTROSCOPY DATA ON LOW-TEMPERATURE DYNAMICS OF ORGANIC AMORPHOUS SOLIDS

A joint analysis of spectroscopic data obtained at liquid-helium tempe ratures by three line-narrowing techniques, photon echo (PE), persiste nt hole burning (HB), and single molecule spectroscopy (SMS), is prese nted. Two polymer systems, polyisobutylene (PIB) and polymethylmethacr ylate (PMMA), doped with tetra-tert-butylterrylene (TBT) were studied via PE and HE techniques and the results are compared with literature data [R. Kettner pr al., J. Phys, Chem. 98, 6671 (1994); B. Kozankiewi cz er al., J. Chem. Phys. 101, 9377 (1994)] obtained by SMS. Both syst ems behave quite differently. In TBT/PIB a rather strong influence of a dispersion of the dephasing time T-2 was found which plays only a mi nor role in TBT/PMMA. We have also measured the temperature dependence of T-2 for both systems in a broad temperature range (0.4-22 K). Usin g these data we separated the two different contributions to the optic al dephasing - due to an interaction with two-level systems and due to coupling with local low-frequency modes. The data are compared with c alculations using a numerical and a semianalytical model in the presen ce of a large dispersion of the single molecule parameters. Furthermor e, we discuss the differences of the linewidths as measured by differe nt experimental methods. (C) 1998 American Institute of Physics. [S002 1-9606(98)50840-9].