Knowledge Bank

The phosphorescence spectrum of pure crystalline naphthalene has been observed both at room temperature and $77\circ K$. The spectrum consists of the 0.0 transition at $4715\backslash AA$ and several intense vibronic bands that correlate well with the most intense vibronic transitions observed in isotopic mixed crystal phosphorescence spectra at $4.2\circ K$. The width of the 0,0 band at half intensity decreases from $270cm-1$ at room temperature to about $75cm-1$ at $77\circ K$, indicating the presence of exciton-phonon interactions in the crystal. Similar narrowing of the vibronic bands is also observed. The triplet state lifetime determined from the decay of the phosphorescence is 130 msec $\pm 15$. Impurities appear to have a significant influence on the triplet exciton behavior even at the relatively high temperatures at which the experiments were carried out.