Identification of the components of the electroluminescence spectrum of PE excited in uniform fields

The electroluminescence (EL) of insulating polymers is a subject of great interest because it gives insight into aging and breakdown processes. While most of the studies performed on polyolefins are under divergent field configurations, a uniform field is used more and more. However, a convincing interpretation of the emission spectrum has not been given up to now, and some discrepancies have appeared between the spectra recorded under divergent and uniform fields. Wavelength-resolved EL spectra are carried out on metalized polymeric films biased under different ac and dc voltage levels. We show that the light emission consists of two different components with typical field dependence and spectral distribution. One is associated with the luminescence of the polymer, the other is due to photon emission from the metallic layers through the radiative decay of surface plasmons excited by the injection current. The proposed interpretation reconciles the observations made under divergent and uniform fields and allows us to discuss the nature of the chromophores involved in EL.