Optical Spectroscopy of Glasses pp 199-265
Models for Reaction Dynamics in Glasses
Glasses differ from crystals in that they lack long-range spatial order. Furthermore, due to their high viscosities, glasses are less favorable to the internal rearrangements displayed by liquids. Hence glasses show a multitude of microscopic patterns around each site (microenvironments), which may relax on widely different time scales. Any local probe of the glass structure, be it an elementary particle (neutron), a trapped charge carrier (electron or hole) or an impurity (ion or sensibilizing molecule) senses not only the different geometry of its surroundings, but, because of it, also changes in the local potentials. These may then reflect themselves in the rates of the processes under investigation. Thus geometrical disorder also implies energetic and temporal disorder. On the other hand, the long lifetime of the local microenvironments precludes an efficient internal averaging; in glasses one is forced to deal with the full complexity of a disordered medium.
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