97_Mizuno_acfield - IEEE Transacfionson Dielectrics and...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
IEEE Transacfions on Dielectrics and Electrical Insulafion vol. 4 No. 4, August 1997 433 Electroluminescence in Insulating Polymers in ac Electric Fields T. Mizuno, Y. S. Liu, W. Shionoya, K. Yasuoka, S. lshii Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Tokyo, Japan H. Miyata and A. Yokoyama Polymer & Chemicals Department, Materials Research Laboratory, Fujikura Ltd , Tokyo, Japan ABSTRACT EL (electroluminescence) in several polymeric materials was investigated in the electric field range < 90 kV/mm. We used polymeric films with semi-transparent gold electrodes: low- density polyethylene, polypropylene, polytetrafluoroethylene and polyvinylchloride. The characteristics were very low inception fields (2 to 20 kV/mm) which strongly depend on the material and very low energy photon emission (mainly in the red region of 1.6 to 1.8 eV). These results reveal that emission occurs predominantly in the metal-polymer interface re- gion rather than in the bulk of the polymer at the applied field. We present a model of EL emis- sion in the metal-polymer interface region to explain our results qualitatively. In this model, the mechanism of emission is the radiative recombination of the electrons and holes trapped at the surface states of the polymer, which causes photon emission in the red region. The in- ception field and EL intensity depend on the density of the surface states of the polymers. 1. INTRODUCTION a low field. We hypothesize that at low fields, carrier injection and LECTROLUMINESCENCE (EL) in polymers has been investigated E and several mechanisms of EL have been proposed [l-41. General- ly, the mechanisms of in polymers have been explained by consider- ing the transport processes of charge carriers, i.e., electrons and holes, in the bulk of the polymer: the conduction of carriers in the conduction and/or valence band of the polymer, and the trapping of these carriers at trapping centers in the band gap. When the applied electric field is high enough to cause charge injection from the electrode into the poly- mer, emission occurs due to the radiative recombination of electrons and holes [1-31 or due to the impact excitation of molecules by acceler- ated electrons [4], during carrier transport in the bulk of the polymer. emission is usually observed at electric fields 2 200 kV/mm in PE (polyethylene) samples with needle-plane or needle-needle electrode arrangement [5,6]. Recentlv, emission has been reported to be observed at a field as II transport and subsequent emission will take place predominantly in the metal-polymer interface region rather than in the hulk of the poly- mer. The energy band structure in the metal-polymer interface region of the polymer has been reported to be different from that in the bulk, based on the measurement of contact charging [S-101. In the metal- polymer interface region many localized states, so-called surface states, are extensively distributed within the band gap of the polymer [8,11, 121. Charge injection into the surface states of polymer has been con- sidered as the contact charging mechanism. In a previous study [13],
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

Page1 / 6

97_Mizuno_acfield - IEEE Transacfionson Dielectrics and...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online