Dynamics of Persistent Hole Burning in Organic Glassesand Its Fractal Interpretation

Abstract

We have derived a non-exponential stimulated photon echo decay function exp (- c T τ D /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 τ 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 1,3,3,1',3',3'-hexamethyl-2,2'-indotricarbocyanine iodide in polyvinyl alcohol (HITC/PVA), and D =2.7 for HITC 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 Γ hole as Γ hole ∝ T 3/ 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.