The absorption and fluorescence spectra of naphthacene molecules in anthracene crystal

Measurements have been made of the absorption coefficients and fluorescence intensities of naphthacene molecules for the a and b crystal axis directions for flakes of anthracene containing naphthacene, and from these the polarization ratios have been obtained. While the ratios for fluorescence approach the values calculated for the oriented gas model, those for absorption are very much lower and this is interpreted as due to mixing of states in the absorption process. It is further concluded that the energy transfer through the crystal is partly by exciton mechanism and partly by quantum mechanical collision.