Dynamics of Persistent Hole Burning in Organic Glasses and Its Fractal Interpretation

We have derived a non-exponential stimulated photon echo decay function exp (-cTτd/3) by assuming that the TLSs of the amorphous host are spatially distributed like a fractal with a fractal dimension D, where c is a constant, T is the temperature and t is the delay time between the first and second excitation pulses. From this function and the measured photon echo decay curves and hole shapes, we obtained D=2.1∼2.3 for l,3,3,l,'3,'3'-hexamethyl-2,2-ndotricarbocyanine iodide in polyvinyl alcohol (HITC/PVA), and D=2.7 for H1TC in ethanol (HITC/EtOH). These values of D are consistent with the possible structures of the long chained polymeric glass and the monomeric glass, respectively. The photon echo decay function also gives a power law temperature dependence of the hole width Γhole as Γhole ∝ T3/D. The deviation of the hole width in HITC/PVA from the power law temperature dependence at high temperatures is explained by a fracton mode of the amorphous host.