Abstract:
The Hamiltonian of double triplet excitations of a molecular crystal is obtained. The permittivity
tensor of a molecular crystal is obtained in the range of frequency of double triplet
excitations. This tensor is expressed in terms of the Fourier transform of the retarded
Green's function, which is found from a system of algebraic equations. It is shown that in
the electric dipole approximation the double triplet states are excited by light through the
excitation of a virtual singlet exciton, which determines the polarization of the absorption
in the given frequency range.