Universal feature of vibrational modes of disordered materials investigated via optical spectra of doped probe molecules

Abstract

We have experimentally determined the density of states of low-frequency host vibrational modes (WDOS)_which couple to the electronic states of chromophores embedded in SiO 2 and SiO 2 TiO 2 gels prepared by a sol-gel method and poly(vinyl butyral). Site-selective excitation spectroscopy has been performed at 4K to obtain the fraction of the zero-phonon line intensity without suffering from spectral hole burning effects. By quantitative analysis of the results, the single-site spectrum and the one-phonon function, which is related to WDOS, have been obtained numerically. It has been found that there exists a universal feature in normalized WDOS of chromophore-embedded amorphous solids of various types.