Spectral analysis of optical emission due to isothermal charge recombination in polyolefins

Abstract

Light emission from electrically stressed polymers, so called electroluminescence, is a subject of great interest because it is associated with electrical aging andl dielectric breakdown of highly insulating materials. Radiative recombination of charge carriers on luminescent centers generally is evoked as the main contribution to the emission, but this is difficult to assess in polyolefins since the spectral features associated with this mechanism are not known. The reason is twofold. First, there is a lack of knowledge on the nature of the luminescent centers in these materials, and second, it is difficult to get wavelengt h-resolved electroluminescence spectra due to the low light level. By using an alternative activation method, we have isolated the emission spectrum associated with isothermal charge recombination in polyethylene and polypropylene. Electrical charges of both polarities are brought to the surface of the samples by contact with a cold plasma powered at a frequency of =5 kHz. The kinetic and spectral features of the recombination-induced emission are recorded after discharge switch off. The recombination mechanism is considered on the basis of the light decay kinetics whereas the chemical nature of the luminescent centers is discussed by a comparison with the photoluminescence spectrum of the polymer. It is shown that charges recombine by tunneling from traps to the luminescent centers which are unsaturated species. The chromophores involved in photo-and recombination-induced luminescence appear to be the same, but not the electronic transitions. Light emitted upon charge recombination has been assigned to transitions from the lowest lying triplet states of poly-enone sequences.

Photoluminescence, recombination induced luminescence and electroluminescence in epoxy resin

“…This regime is clearly defined from More interestingly, it is also found that fluorescence is not excited during charge recombination. This behaviour has been found in all the polymeric materials studied so far [13,14]. The absence of fluorescence in recombination-induced luminescence can be explained in various ways.…”

Space charge and associated electroluminescence processes in XLPE cable peelings

“…The AC spectrum is shown in Figure 3, where it is compared with the spectrum of the light emitted by the same XLPE material during the recombination of positive and negative charges, in the absence of an applied field (i.e. the excitation mechanism cannot be due to hot carriers) [6]. Even if all the spectral features of the EL spectrum cannot be fully interpreted on the basis of the so-called recombination-spectrum, it is clear that the latter is a component of the former.…”

Investigating the inception mechanism of pulsed x-ray triggered partial discharges by time resolved measurements

“…The electroluminescence processes taking place in a discharge have been mostly studied with respect to their spectral characteristics [36][37][38][39], but precise data about the duration of these individual processes is missing. It is generally known during ionization events in a gas, processes like photoluminescence and radiative recombination take place [38].…”

“…It is generally known during ionization events in a gas, processes like photoluminescence and radiative recombination take place [38]. Their electroluminescence is very much related to the gas type and other parameters like temperature and electric field.…”