Photochemical holes: A spectral probe of the amorphous state in the optical domain

Abstract

The optical line shape features of dye molecules are used for probing some low temperature properties of amorphous solids. The experimental technique is photochemical hole burning (PHB); the dye molecule is 1,4-dihydroxyanthraquinone. The results obtained for ethanol glasses and boric acid glasses are as follows: The optical linewidth obeys a T2 law. It has two contributions: one reversible contribution due to fast dephasing processes, and one irreversible contribution due to ground state redistribution processes. The latter contribution will be interpreted in terms of the TLS model (two-level system) which has been commonly used to describe the amorphous state. One main conclusion is that the energy asymmetry distribution of the TLS systems is rather narrow (several cm−1). A second conclusion follows from the absence of a sizeable isotope effect upon deuteration of the samples. We must assume that proton tunneling is not the main mechanism involved in the TLS dynamics.