Comparison between photo-, cathodo-, and electro-luminescence spectra of polyethylene naphthalate films and relationship with electrical aging

This work is a contribution to the identification of the spectral components observed in the electroluminescence (EL) of insulating polymers. The approach aims at improving our current understanding of the nature of the interactions between electrical charges and the host material. In previous studies of poly(ethylene 2,6-naphthalate)-PEN, we have shown that some spectral features of the light emitted under high field could be associated with polymer degradation since they are not characteristic of the photophysical behavior of the material as probed by using mild UV-photons in photoluminescence experiments. So long as the nature of the degradation mechanism is not identified, support to this hypothesis can be brought considering other sources of excitation of the material that are likely to produce significant chemical degradation. Cathodoluminescence has been used in this respect, and a comparison between electro-, photo-, and cathodo-luminescence spectra is proposed. Some features of the EL spectrum that cannot be interpreted on the basis of the photoluminescence spectrum are present in the cathodoluminescence spectrum. Consideration of the excitation mechanisms in the three kinds of experiment gives conclusive evidence of material degradation signatures in the EL spectrum.