Fluorescence and phase transition of p-terphenyl crystal

The fluorescence and the excitation spectra are reported for the p-terphenyl crystal in the temperature range from 300 to 5 K. The appearance of a new band at 335 nm in the fluorescence spectrum and the large blue shift of the excitation spectrum, 1200 cm^-1, on lowering the temperature are explained by the displacive-type phase transition in a wide temperature range, 191-20 K, where the dihedral angle θ of the TP molecule increases uniformly and continuously.