ELECTRONIC STATES OF MIXED MOLECULAR CRYSTALS

In this paper we consider the energy levels of dilute mixed crystals in the weak vibronic coupling limit using the one-particle Green's-function method. The perturbation Hamiltonian is treated explicitly with reference to impurity molecules differing from the host molecules by isotopic substitution. The general equations derived for the energy levels, for excitation amplitudes, and for the optical properties of the mixed crystal are expressed in terms of the weighted density-of-states function of the pure crystal. This treatment emphasizes the relation between the density of exciton states in the pure crystal and the optical properties of mixed crystals. The nature of bound and virtual impurity states are considered, and new experiments using the impurity-induced electronic-absorption method are suggested.