Excimer and Monomer Defect Emissions of Perylene and Pyrene Crystals as Studied by the Nanosecond Time-resolved Spectroscopy Technique

Nanosecond time-resolved fluorescence spectra were measured at 77°K for pyrene and perylene crystals, and anomalous emissions which have lifetimes of ∼ 8 nsec and are difficult to be found by the usual steady excitation, were observed at the higher-wave number sides of the usual excimer emissions. From the band position and the vibrational structure, the anomalous emission was interpreted as being due to monomer defects in each crystal. The analysis of the observed rise and decay curves of the monomer defect and excimer emissions shows that the excited states of both emissions are populated independently from the band level of each crystal excited by light irradiation. The temperature dependence of the emission indicates that a thermal activation of 0.035 eV is required for the excimer formation in a perylene single crystal, while no activation energy is required for the excitation of the monomer defect.