Electroluminescence in polyethylene subjected to impulse voltages

Electroluminescence (EL) from HDPE (high-density polyethylene) films subjected to repetitive rectangular-shaped impulse voltages has been investigated at electric fields <80 kV/mm in order to clarify the temporal behavior of carriers injected into the polymer. EL emission was distinctly observed during the voltage rise and fall phases. During the voltage plateau and the zero voltage phases, the EL intensity did not instantly decrease to zero but a very weak EL emission lasted for at least 3 ms. The number of EL pulses was determined by the amplitude of the impulse voltage, whereas the EL intensity strongly depended on the temporal variation rate of the voltage. The total number of EL pulses during both phases of the voltage rise and fall was almost equal. The EL spectra did not depend on the phase and the amplitude of the impulse voltage. The above behavior of EL emission can be explained qualitatively by the electron-hole recombination in the metal-polymer interface region and showed the picture of temporal behavior of carriers, carrier injection and transport, in the interface region for the field relaxation at the interface.