Understanding optical emissions from electrically stressed insulating polymers: Electroluminescence in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate) films

Wear-out and breakdown of polymers used as insulating materials are closely related to the dissipation of electrostatic energy in space charge regions. A fraction of this energy is radiated off by electroluminescence which can be considered as a pre-breakdown warning and provides a probe to investigate the mechanisms leading to structural degradation. Electroluminescence emission from two aromatic polyesters is studied-poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate). We investigate the excitation processes of the luminescent centres, the nature of the centres, and the relationship of the emission features to electrical ageing. Sample electroluminescence is excited by de and ac voltages under a uniform field configuration. The discussion relies on the analysis of the charge transport process in the luminescent regime, the acquisition of electroluminescence and photoluminescence spectra, and the investigation of the field effect on photoluminescence.