Electroluminescence measurements of low-density polyethylene (LDPE) films subjected to high electrical stresses in different gas environments

It has been proposed that the measurement of the characteristics of electroluminescence (EL) observed during the application of ac and dc electric fields across thin films of polymeric material can be used to probe the early stages of electrical ageing. Both EL and electrical ageing of the polymer are thought to arise due to the injection of charge carriers into the material from the metallic electrodes. However, before changes in the EL characteristics can be properly assigned to polymeric ageing, it is necessary to understand the physical processes that give rise to EL. In this paper, the effect of absorbed gases N₂ and SF₆ on the EL characteristics of low density polyethylene were examined. It was found that the EL can be split into two different spectral components, C₁, having a broad peak centered at a wavelength between 550 and 600 nm, and a second component, C₂, having a peak wavelength greater than 700 nm. The intensity of the C₁ component of EL was found to depend on the type absorbed gas present in the material while the intensity of the C₂ component was found to be independent. The results demonstrate that the electronegativity of the absorbed gas plays a fundamental role in the formation of excited states and subsequent recombination in the case of the C₁ emission while the C₂ emission supports the conjecture that this is due to the excitation of surface plasmons at the dielectric/polymer interface.