Optical dephasing in doped organic glasses over a wide (0.35-100 K) temperature range: Solid toluene doped with Zn-octaethylporphine

摘要

We have performed optical photon echo measurements on amorphous toluene doped with zinc-octaethylporphine over a wide temperature interval (0.35-100 K). This broad temperature range, reaching from subkelvins up to the Debye temperature of toluene (100.7 K), enabled a clear separation between the low and high temperature contributions of line broadening processes to the total optical dephasing. The high temperature part of the measured dephasing times was analyzed using recent data from light scattering experiments which determined the spectrum of low-frequency modes of the toluene matrix. The analysis shows that two line-broadening mechanisms contribute mainly to total dephasing: the tunneling transitions of two-level systems, which lead to a power-law temperature dependence of the linewidth at low temperatures (T<3-4K), and the interaction of the chromophore with low-frequency phonon modes of the glassy matrix, which gives rise to an exponential behavior at high temperatures. It was shown that the contribution of acoustic phonons to optical dephasing in the studied system is negligible over the whole temperature region of the measurements.