Theory of band and bound states of double triplet excitations in molecular crystals. II

An investigation is made of the system of algebraic equations for the Green's functions that are used to express the permittivity tensor of a crystal in the region of frequencies of double triplet excitations. The ratio of the strength of the interaction between molecules in triplet excited states to the magnitude of the resonant transfer of triplet excitation energy through the crystal determines whether bound (“single-particle”) states of two triplet excitations (excitons) or band states make the main contribution to the absorption of light. In the case of a one-dimensional crystal explicit expressions are obtained for the energy of the bound states together with formulas that describe the intensity of band absorption and absorption by bound states. An investigation is made of the effect of Davydov splitting in the range of frequencies of the excitation of bound states of two triplet excitons and the effect of the sensitivity of the band width of the double excitations to polarization.