Electroluminescence and thermo-stimulated luminescence in an epoxy resin under uniform ac field

The critical field beyond which irreversible evolution of a material occurs and how this limit varies with temperature is of prime importance from the insulation designer's standpoint. The present work concerns electroluminescence (EL) measurements for an epoxy resin under uniform 50 Hz ac field. We have studied the EL dependency on both temperature (20 to 72/spl deg/C) and electric field (0 to 16 kV/mm) under ac stress. The material investigated does not contain mineral fillers, and has a glass transition temperature of 65/spl deg/C. We have observed two regions in the EL-field characteristics: a low field regime in which the EL threshold appears limited by the sensitivity of the detection set-up, and a higher field regime, above a threshold in the range 8 to 14 kV/mm, with a higher slope in the characteristics. We have also observed a strong spontaneous light emission in the absence of applied voltage. The origin and consequences of this on EL are discussed.