Crystallization and excitonic luminescence of coronene crystals

The authors have obtained single-crystal flakes with dimensions approximately 5 mm * 1.0 mm. The major impurity in commercial coronene has been removed by recrystallization from benzene solution. Other unknown impurities were removed by zone refining combined with a sublimation technique. The molecules in the coronene crystal are stacked closely and parallel to each other. A feature that one expects from the stacked molecular arrangement is a strong exciton-phonon interaction. Luminescence spectra were consistent with this suggestion, indicating that free excitons relax quickly to a self-trapped state which is shallow.