Long Time Phosphorescence of Organic Crystals

Long time phosphorescence (of the order of minutes) of anthracene, stilbene, durene, and naphthalene crystals at room temperature is reported. The decays are approximately hyperbolic and the observed phosphorescence is shifted to longer wavelengths than the usual fluorescent emission. This phosphorescence is not induced by the light strongly absorbed in the substance but mainly by the weak absorption of light of wavelengths corresponding to their own fluorescent light. There are indications that this phosphorescence stems from an approximately uniform, continuous trap distribution and that such a mechanism permits a description of some of the observed behavior. Wavelength measurements seem to indicate that this phosphorescent light emission does not originate from triplet to ground transitions.