THE POLARIZED FLUORESCENCE OF VERY THIN ANTHRACENE CRYSTALS

Abstract

The polarized fluorescence from anthracene sublimation flakes has been measured at 300°, 77°, and 4 °K. A recording spectrometer was used to measure accurately the relative intensity of the two crystal polarizations and also to determine changes in the spectrum between 77° and 4 °K. The polarization ratio (b/a) was found to decrease with increasing wavelength and measurements made at 77° and 4 °K. indicate that there is more than one emitting level and that these have different polarization properties. The fluorescence arises from regions of weak absorption in the crystal and it is suggested that these regions occur in the neighborhood of imperfections. In addition the polarized fluorescence excited from anthracene sublimation flakes containing traces of tetracene has been determined and changes were found in the transfer efficiency between 77° and 4 °K., again suggesting the presence of more than one emitting level. No depolarization of the tetracene fluorescence was observed at low temperatures.