The existing interpretation and models of electroluminescence
(EL) in poly(ethylene-2, 6-naphthalate) (PEN) suggest a mechanism
triggered by the impact excitation and/or ionization of the luminescent
centres by hot electrons. Excitation by bipolar charge recombination has
not been considered extensively because of the lack of knowledge of the
behaviour of electrons and holes in insulating films subjected to a dc
stress. An investigation of the internal space charge distribution versus
field is believed to constitute a relevant approach to discussing the EL
excitation process. Transient and steady-state EL of PEN films are
analysed with the support of space charge profiles obtained by the laser
induced pressure pulse (LIPP) method for dc fields in the range of
25-225 kV mm-1. For field values up to 75 kV mm-1, the internal
charge is dominated by dipolar polarization without any excitation of EL.
Space charge polarization is evidenced from 75 kV mm-1 upwards, the
LIPP response being a superposition of space charge and dipolar
polarization effects. Space charge polarization dominates in the field
range where EL is continuously emitted (E>150 kV mm-1). The EL
excitation mechanism is discussed on the basis of the recorded charge
profiles.
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