Measurement of degree of polarization of fluorescence of pure anthracene crystalline film

The polarization ratio (I _b/I_a) of fluorescence of a monocrystalline film of pure anthracene is measured correcting for all probable errors. Comparison with decay-time data brings out that deviation from the value obtained from absorption measurements is due to a loss of intensity in the a-polarized fluorescence as compared to what is expected from absorption data. This is interpreted as an evidence that anthracene crystal fluorescence is emitted from regions of local lattice imperfections. It is confirmed that the first electronic transition takes place along the short axis of the anthracene molecule.