96_Laurent_ELf_spectruralfeature

96_Laurent_ELf_spectruralfeature - IEEE bansactions on...

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IEEE bansactions on Dielectrics and Electrical Insulation Vol, 3 No. 6, December 1996 859 Spectral Features of the Luminescence I PE Subjected to Various Excitation Sources 1 J. Jonsson and B. Rinby F. Massines, D. Mary and C. Laurent Department of Polymer Technology, Royal Institute of Technology, Stockholm, Sweden Laboratoire de Genie Electrique, Universite Paul Sabatier, Toulouse, France ABSTRACT Electroluminescence (EL) of insulating polymers is now recognized as a warning sign for electrical aging. In order to further understand the emission process, we have compared the luminescence spectra of the same material when the emitting states are created by dif- ferent excitation sources. Additive free and carbonyl containing low density polyethylene films were used. Light emission was stimulated by photon irradiation in the ultraviolet range (photoluminescence), by the interaction between a cold plasma and the polymer surface leading to a post-discharge emission (plasma induced luminescence), and by the electric field in the absence of any gaseous discharge (EL). Plasma induced luminescence and electroluminescence exhibit similar spectral features in the wavelength range be- tween 500 and 650 nm. It is concluded that the same kind of chromophores is involved in both processes. They could be conjugated groups acting as recombination centers because charges are selectively trapped on these groups. This explains why photoluminescence does not show similar emission features since all the material chromophores are excited upon UV irradiation. Moreover, it is shown that the EL-features are sensitive to structural relaxation of the polymer probably through the interaction between emitting species and the surrounding molecules. INTRODUCTION E the pioneer work by Hartman and Armstrong in 1967 [l], troluminescence (EL) has been reported in many different s [2-61. It is of crucial importance in the study wn because light emission is a direct proof of very reactive states far from thermodynamic efore considered as a warning sign for elec- gradation. Most models proposed for EL argue that either nation (electron-hole) or impact ionization (hot electrons) ion. There is still much controversy on this occurrence of one or the other excitation mechanism xtent on the material properties and elec- , the nature of the luminescence centers has not been identified so far, mainly because the weak intensity that does not allow straightforward n order to overcome this problem, we have rable EL features with the light emitted by the other excitation sources are used to stimulate considered two alternative ways to excite ce: photon irradiation, which induces pho- ce (PL), and cold plasma treatment, where the light ce excitation by the plasma. In this later alled plasma induced luminescence (PIL).
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96_Laurent_ELf_spectruralfeature - IEEE bansactions on...

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