AC electroluminescence spectra of Polyethylene Naphthalate: Impact of the nature of electrodes

One of the unresolved questions in the EL spectrum of insulating materials in general is the occurrence of red emissions under AC electric field when using e.g. silver or gold as metal electrodes. Surface plasmons (SPs) effects and/or charge recombination on surface states have both been advocated as possible origins for such emissions. In this contribution, EL of 25μm Polyethylene 2, 6-Naphthalate (PEN) films are investigated using Indium Tin Oxide (ITO) and gold (Au) electrodes separately, the singularity of ITO being that it does not exhibit the SPs effects characteristic of noble metals (e.g. gold) in the visible domain. EL spectra and EL-field characteristics were recorded under DC and AC fields, as well as phase-resolved EL patterns. Emission spectra from ITO-PEN-ITO do not reveal the red emission contrary to that of Au-PEN-Au. Results are discussed regarding both the origin of the emissions, and the consequences that SPs-mediated emissions may have on EL features such as EL-field characteristics, spectra, and phase patterns.