Phosphorescence Spectrum of Pure Crystalline Naphthalene

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Abstract
Phosphorescence spectra of pure crystalline naphthalene at room temperature and at 77°K are presented. In addition to the 0, 0 transition at 4715 Å, the spectra show several intense vibronic bands that correlate well with the most intense vibronic transitions observed in isotopic mixed‐crystal phosphorescence spectra at 4.2°K. The width of the 0, 0 band at half‐intensity decreases from 270 cm−1 at room temperature to about 75 cm−1 at 77°K, indicating the presence of exciton–phonon interactions in the crystal. Similar narrowing of the vibronic bands is also observed. Using incident light of sufficient intensity to permit the weak phosphorescence to be observed, the intensity ratio of delayed fluorescence to phosphorescence is found to be approximately 100:1 both at room temperature and at 77°K. The triplet state lifetime defined by the first‐order component of the phosphorescence and delayed fluorescence decays is 130 msec and shows almost no temperature dependence. The lifetime is about six times longer than previously reported values. Impurities appear to have a significant influence on the exciton behavior even at the relatively high temperatures at which the experiments were carried out.