Theory of Electronic Energy Relaxation in the Solid Phase

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Abstract
A theory of electronic energy relaxation in the solid phase is presented. This process is sometimes called internal conversion when applied to states of the same multiplicity, or intersystem crossing when applied to states of different multiplicity. The physical limit where the electronic transition is slow compared with vibrational relaxation is shown to be a well‐defined mathematical limit in the theory. In the other limit, where the electronic transition is rapid compared with the vibrational relaxation time, vibrational relaxation plays the dominant role in the over‐all relaxation process. The result derived from a continuum model for the final states is justified only in the first limit and only then providing the assumption of a large number of final states is physically justified. Two different models are used to illustrate the source of the mathematical limitations and the range of applicability of the theory. These models remove the ambiguities which arise from the normalization of continuum states in the continuum model. The most important conclusions of the paper are embodied in Eqs. (22), (23), (40), (48), and (50).