Frenkel exciton states in microcrystallites

A theory of Frenkel exciton states in microcrystallites based on a model of the nearest neighbor interaction is developed. The theory is applied to calculate the k = 0 component in the density of states in aromatic microcrystallites, whose characteristic feature is an intense sharp band followed by a high-energy exponential tail. The theory also explains satisfactorily the spectral width of the excitation spectra, which reflects the exciton bandwidth of bulk crystals.