We generalize our recent work on the optical bistability of thin films ofmolecular aggregates [J. Chem. Phys. 127, 164705 (2007); arXiv:0707.1264v1[cond-mat.dis-nn]] by accounting for the optical transitions from theone-exciton manifold to the two-exciton manifold as well as the exciton-excitonannihilation of the two-exciton states via a high-lying molecular vibronicterm. We also include the relaxation from the vibronic level back to both theone-exciton manifold and the ground state. By selecting the dominant opticaltransitions between the ground state, the one-exciton manifold, and thetwo-exciton manifold, we reduce the problem to four levels, enabling us todescribe the nonlinear optical response of the film. The one- and two-excitonstates are obtained by diagonalizing a Frenkel Hamiltonian with an uncorrelatedon-site (diagonal) disorder. The optical dynamics is described by means of thedensity matrix equations coupled to the electromagnetic field in the film. Weshow that the one-to-two exciton transitions followed by a fast exciton-excitonannihilation promote the occurrence of bistability and reduce the switchingintensity. We provide estimates of pertinent parameters for actual materialsand conclude that the effect can be realized.
展开▼
