Role of the structure on the photo and cathodo-luminescence of poly(ethylene naphthalate): PEN

The photoluminescence in the blue emission band at 430 nm of poly(ethylene naphthalate), assigned in literature to the formation of excimers states in volving the naphthalene groups, is shown to be very sensitive to the disord er induced by irradiations. The cathodoluminescence, excited by a beam of 4 keV electrons, exhibits two components: a rapidly decreasing fluorescence at 430 nm and a broad and more stable one at 640 nm assigned to short chain segments. The influence of mechanical stretching and temperature on the fl orescence of non-treated PEN films has been investigated. The enhancement o f the fluorescence with film elongation is attributed to the increase of th e polymer chain ordering along the stretching direction, whereas the decrea se of the fluorescence with temperature is correlated to the beta* relaxati on associated in dielectric spectroscopy to the movements of the naphthalen e groups, known to be responsible for the excimer fluorescence. The depende nce of the blue and red fluorescence components on the polymer structural o rganization provides efficient probes to study the local order and degradat ion stage of PEN and accounts for the results reported in literature accord ing to the different film histories. (C) 2000 Elsevier Science S.A. All rig hts reserved.