Dynamics in disordered materials probed through optical spectra

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From the resonance fluorescence spectra measured for dye molecules in organic molecular glasses at low temperatures, we determined the density of states of vibrational host modes weighted by the electron-phonon coupling strength for each sample. The normalized shape of this weighted density of states was found to exhibit the quantitatively universal feature which coincides with that obtained for dye-doped organic and inorganic amorphous polymers, though the nature of disorder is widely varied among the materials. Raman scattering spectra were also measured for host glasses at low temperatures. Although the same kind of materials showed similar spectral shapes, remarkable difference was found among the groups of materials. These results indicate crucial importance of classifying types of vibrational modes in order to clarify the low-frequency dynamics of disordered materials and also suggest that a certain class of dynamics shows universality, the origin of which should be clarified in the future study.