From the resonance fluorescence spectra measured for dye molecules in
organic molecular glasses at low temperatures, we determined the densi
ty of states of vibrational host modes weighted by the electron-phonon
coupling strength for each sample. The normalized shape of this weigh
ted density of states was found to exhibit the quantitatively universa
l 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 measur
ed for host glasses at low temperatures. Although the same kind of mat
erials showed similar spectral shapes, remarkable difference was found
among the groups of materials. These results indicate crucial importa
nce of classifying types of vibrational modes in order to clarify the
low-frequency dynamics of disordered materials, which will be discusse
d taking account of recent studies in the literature. (C) 1998 Elsevie
r Science B.V. All rights reserved.