In one-dimensional (1D) molecular crystals with finite length 2L #lambda#(#lambda# is the optical wavelength) an overwhelming part of the total oscillator strength is concentrated in the lowest excitonic state and is equal to F_1 approx = 0.85 f_0 (2L/a), where f_0 is the oscillator strength of a monomer and a is the lattice constant. This leads to the superradiance from the lowest excitonic state and its domination in the absorption spectrum of the crystal. We show that self-trapping of excitons destroys this simple picture so that it takes place only for short chains with length 2L small as compared to the length 2l_0 of self-trapping. For long enough chains the value of F_1 does not increase with growth of L, as it occurs in linear case, but tends to the saturation limit F_1 approx = 5 f_0 (l_0/a). The osciallator strength of the next bright state also tends to the same limit with growth of L, but it takes place only at the length L>9l_0, and analogous relations are true for the following bright states. We consider also the influence of quantum confinement and self-trapping on the superradiance of 1D molecular crystals.
展开▼
