Densities of states and band widths of excitons in anthracene microcrystallites embedded in PMMA Original Research Article

A new technique to determine the k = 0 components in the density of states (DOS) and band widths of excitons in microcrystallites is demonstrated. Applying the technique to anthracene microcrystallites, it is found that DOS shows up as a broad tail which extends towards higher energies, in addition to sharp peaks. The width of the tail, representing the exciton band width, takes its maximum value of 340 cm−1 for microcrystallites of 65 Å, but it becomes narrower as the size of microcrystallites reduces. For microcrystallites with a diameter larger than 65 Å, the observed band width decreases asymptotically to 300 cm−1, which represents the band width of a bulk crystal.