ABSORPTION AND FLUORESCENCE SPECTRA OF CRYSTALLINE TRANS-STILBENE

Measurements on polarized absorption and fluorescence of a single crystal of trans-stilbene are reported. Vibrational analysis is also reported for them. The a:b polarization ratio in the absorption of a pure trans-stilbene crystal deviates greatly from the oriented gas model value. The fluorescence origin of the pure crystal at 300°K is 340 cm-1 to the long-wavelength side of the 0-0 absorption band. On lowering the temperature to 90°K the intensity of fluorescence near the origin decreases and a red shift of 50 cm-1 to 100 cm-1 is found. It is suggested that the fluorescence is due to a trapped exciton located at some lattice imperfection and that, at low temperature, a part of the fluorescence originates from a lower defect level.