Free-Exciton Luminescence and Weak-Exciton Scattering in Coronene Crystals

Abstract
Luminescence and absorption spectra of coronene single crystals are studied. Free-exciton luminescence is observed for the first time. The intensity of free-exciton luminescence decreases with decreasing temperature, suggesting that free excitons are in thermal equilibrium with excitons in a relaxed state which is located 1070 cm -1 below the bottom of the free-exciton band. The line shape of the O–O absorption band which is located at 23220 cm -1 at 10.4 K is Lorentzian, indicating that scattering of excitons by phonons is weak.

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