UNIVERSAL FEATURE OF VIBRATIONAL-MODES OF DISORDERED MATERIALS INVESTIGATED VIA OPTICAL-SPECTRA OF DOPED PROBE MOLECULES

We have experimentally determined the density of states of low-frequen cy host vibrational modes (WDOS) which couple to the electronic states of chromophores embedded in SiO2 and SiO2-TiO2 gels prepared by a sol -gel method and poly(vinyl butyral). Site-selective excitation spectro scopy has been performed at 4K to obtain the fraction of the zero-phon on line intensity without suffering from spectral hole burning effects . By quantitative analysis of the results, the single-site spectrum an d the one-phonon function, which is related to WDOS, have been obtaine d numerically. It has been found that there exists a universal feature in normalized WDOS of chromophore-embedded amorphous solids of variou s types.