Linewidths In Spectra Of Terrylene In Polyethylene Probed By Incoherent Photon Echo. Comparison With Single Molecule Spectroscopy Data

The concept of the homogeneous spectral linewidth of an impurity center is more complicated in disordered media such as organic glasses and polymers than it is in crystals. In amorphous media the local environments for impurity centers are continuously changing with time. As a result transition frequencies of individual centers diffuse within the inhomogeneous broadened spectral contour, which is called spectral diffusion. When the timescale for spectral diffusion processes is much longer than the dephasing time, it is possible to distinguish homogeneous dephasing from spectral diffusion. On the other hand, when the timescales of spectral diffusion and dephasing processes are comparable these phenomena become indistinguishable.