Photoluminescence and Raman spectra study of para-phenylenevinylene at low temperatures

The photoluminescence and Raman spectra of poly (para-phenylenevinylene) (PPV) have been investigated at low temperatures down to 83 K. With decreasing temperature the photoluminescence spectra peaks are shifted to the lower energy side while the peak intensities are enhanced. The fitted Huang-Rhys parameter for the conjugated length has indicated that the conjugated length is elongated by 2.2 repeat units from 294 to 83 K. Though a distinct shift for the Raman band frequencies was not found, the Raman band intensities are, however, intensified at low temperatures. The Raman band intensity ratio I-1548/I-1626 is enhanced with decreasing temperature, indicating that the disorder is reduced and the conjugated length is increased at low temperatures.