Role of additives as recombination centres in polyethylene materials as probed by luminescence techniques

The long-term electrical stability and dielectric breakdown of insulating polymers is largely determined by the density and energy distribution of the conduction and trapping levels. Although these materials are widely used in technical applications very little is known about the nature of the deep trapping centres which are responsible for charge storage. We show that luminescence techniques can be used to gather information on their nature. The proposed approach relies on photo- and recombination-induced luminescence experiments. The latter has been specifically developed to record the optical spectrum of the emission radiated by a deep trapping centre during a recombination event. The work concerns low-density polyethylene, doped or undoped, and cross-linked polyethylene. It is shown that the implication of a given chemical in the trapping process can be probed by using the recombination-induced luminescence technique.