Jean Farenc

PRESSURE DEPENDENCE OF ELECTRICAL AND OPTICAL CHARACTERISTICS OF ALQ3 BASED ORGANIC ELECTROLUMINESCENT DIODES

Organic electroluminescent diodes based on thin organic layers are one of the most promising next-generation systems for the backlighting of liquid crystal screens. In the literature, conduction has been interpreted in terms of tunneling or as a space charge limited process. To clarify this point we carried out an experimental study of the electrical and optical characteristics, as a function of the applied voltage, for different hydrostatic pressures. Results show that tunneling is the dominant mechanism which controls the organic light emitting diodes efficiency.

Electronic conduction in electropolymerized carbazole thin films

The electronic conduction mechanism in polycarbazole (PCz) films was investigated. Electropolymerization was used to fabricate PCz thin films. The current density versus the electric field J(E) indicated an ionic polarization. Ions were (1) quenched by the effect of a high hydrostatic pressure or (2) eliminated by dipping PCz in de-ionized water. The electronic conduction was characterized by J(E) measurements at different temperatures and by impedance spectroscopy, and was modelled as a Schottky-type injection. A comparison of the results obtained following treatments 1 and 2 indicated a large difference in the model parameters. This disparity was interpreted in terms of differences in the effective mass due to interface modification.

A fluorescent plastic optical fiber sensor for the detection of corona discharges in high voltage electrical equipment

The reliability of electrical equipment in high voltage systems can be affected by certain defaults (metallic particles, roughness, etc.) inside the device enclosure. These anomalies may cause a local glow discharge which propagates progressively inside the insulator and which can lead to electrical breakdown. To avoid this end result, corona discharges have to be detected with a system which satisfies some requirements. Actual methods are not well adapted to industrial constraints. An optoelectronic setup, consisting of a fluorescent plastic optical fiber as a light sensor, connected to a simple, low‐cost amplifier, is proposed. Measurements were first carried out in air to demonstrate the feasibility of this detection method, then air was replaced by SF6. Results lead to the delineation of a sensor made of the fluorescent fiber and the associated amplifier.

X‐ray sensor based on a plastic optical fiber for monitoring high voltage interrupters

An x‐ray sensor based on a fluorescent plastic optical fiber is described. The core is doped with an organic fluor while double cladding contains an inorganic product (ZnS) converting x‐ray energy into visible light. The light emitted by the sensor is guided by a commercial PMMA fiber to a photodiode whose signal is amplified. The electronics have been optimized to increase sensitivity and reduce noise. The paper indicates the methods used to prepare fibers. It describes their characterization and gives the main characteristics of the amplifier. The sensor is used to visualize the x‐rays emitted by vacuum interrupters during switching. Signal modification gives us information on the surface degradation of the electrodes. Among other advantages, the sensor can be used on site, without disconnecting the interrupter.