Free Volume Model of Thermally Induced Spectral Diffusion

Abstract

An organic dye/polymer system, such as free base phthalocyanine (H2Pc) dispersed in polymethylmethacrylate (PMMA), has been interested in as a model material of new mass-storage for photochemical hole burning (PHB)[1]. There are, however, some unsolved problems in applying it to a plactical memory system. That is, the influence of polymers as a matrix over the static and dynamic properties of the system, such as, thermally induced spectral diffussion (TISD), homogeneous and inhomogeneous line width, burning efficiency and so on, has not been solved yet. TISD among them has a strong correlation to micro environment of a polymer dispersing a dye. The disorders in amorphous polymers are seen in wide energy range whose upper limit is determined by the glass transition of polymers. However, the lower limit is still left unknown , although some phenomena are known which are affected by low energy excitation. Recently, hole burning spectroscopy was successfully applied to investigate in the lower energy region [2]. Thermally induced conformation changes of polymers are said to have energy of same size to cause TISD in the lower energy region. Koehler et al. succeeded in explaining the the changes quantitatively from a combination of three independent processes, 1- phonon tunneling process, 2-phonon Raman scattering process and activation process [3]. The material parameters, however, that determine the changes are still unknown. We report TISD results of some dye/polymer systems and correlation between TISD and polymer properties.