Line broadening mechanisms in spectra of organic amorphous solids: photon echo study of terrylene in polyisobutylene at subkelvin temperatures

We have developed an experimental setup with a 3He bath cryostat for picosecond photon echo (PE) measurements in a broad range of temperatures. In this Letter, a two-pulse PE investigation of the amorphous polymer polyisobutylene (PIB) doped with tetra-tert-butylterrylene (TBT) in the temperature region 0.4–4 K is presented. The results are compared with single-molecule spectroscopy (SMS) data for the same system. The PE yields a linewidth which is close to the average of the SMS linewidth distribution. We conclude that a dispersion of the dephasing time T2 contributes significantly to the linewidth distribution as measured by SMS. Furthermore, the temperature dependence of the linewidth is analyzed.