Temperature dependence investigation of the electron paramagnetic resonance of the photorefractive polymer BisA-NAS:DEH

摘要

Abstract: The photorefractive BisA-NitroAminoStilbene polymer (BisA- NAS:DEH) has drawn much attention in recent years due to its potential applications such as terabyte optical data storage, real time optical processing, image amplification, and dynamic holography. Extensive optical investigation for this polymer was performed mostly at room temperature. On the other hand less attention was given to the behavior of this polymer at much higher or lower temperatures than the room temperature. Using the electron paramagnetic resonance technique and a home built temperature controller (minus 190 to 500 degrees Celsius) we have been able to study the temperature effect on the spin concentration of BisA-NAS:DEH in the temperature range from 100 to minus 190 degrees Celsius. An anomalous behavior for the EPR signal was observed near 70 degrees Celsius as the spin density increases drastically especially around 85 degrees Celsius. Also, around minus 25 degrees Celsius the main EPR signal broadened then splits into a doublets which are quenched at higher temperatures. Preliminary interpretation of this signal is given on the basis of behavior of the NAS dye molecule at higher temperature and the transport agent DEH which transfers the charge generated at the dye molecule to the other part of the material, and thus coupling the process of photoconduction. !8