Luminescence from interacting Frenkel excitons at high-level optical excitation

Frequency-resolved spontaneous light emission (SLE) from a system of interacting Frenkel excitons excited with high-intensity optical radiation has been investigated. Application of nonequilibrium diagram techniques allows us to address the problem of computation of the SLE cross section by solving the Dyson equation. In the lowest order for the self-energy part, the forward scattering and the luminescence components of SLE cross section are distinguished. The angular distribution of the luminescence is analyzed in detail for the simplest case of a cubic crystal. It is also shown that the multiphoton absorption process produces an exciton density that affects the absorption and the emission line shape (exciton dynamic Stark effect) as well as the nonradiative dephasing rate. This dependence corresponds to a nonlinear relation between the luminescence and the incoming radiation intensities.