Temperature dependence of the optical homogeneous width of mesoporphyrin and its aggregate in polyvinylalcohol at 1.8-50 K

The temperature dependence of the optical homogeneous width was investigate d for mesoporphyrin and its aggregate doped in polyvinylalcohol from 1.8 to 50 K by means of persistent spectral hole burning and accumulated photon e cho. Because the exponent of the temperature dependence changes around 10 K , there exist two dephasing mechanisms that are characteristic for amorphou s polymers. At lower temperatures, phonon-assisted tunneling of two-level s ystems (TLS) is dominant. On the other hand, the Raman process of low-frequ ency phonons is dominant at higher temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.