Electron paramagnetic resonance and in situ photosensitivity investigation of the photorefractive polymer BisA-NAS:DEH

Abstract

We have observed the electron paramagnetic resonance (EPR) signal in the photorefractive polymer BisA-NAS:DEH. The polymer is a mixture of the electro-optic polymer bisphernol A 4,4-nitroaminostilbene (BisA-NAS) with 29% by weight benzaldehyde diphenyl-hydrazone (DEH), a hole transport agent. The EPR signal was observed at 3431.590 G. Illumination of the photorefractive polymer by an Ar+ laser leads to an interesting phenomenon. With an aim to understand the photosensitivity of the photorefractive polymer, we have monitored the changes in the intensity of the EPR line. The measurements were done in situ at room temperature and liquid nitrogen temperature 77 K. The sample was loaded in an optical transmission cavity to facilitate the use of the laser. When the sample is illuminating with low laser intensity, illumination decreases the EPR signal while for higher laser intensity, the EPR signal grows. We provide a tentative explanation for this phenomenon. Low laser intensity introduces photoconductivity, which reduces the EPR signal, but does not create free radicals. For higher laser intensity, paramagnetic free radicals are formed contributing to the increase of the EPR signal. The relation between observed phenomenon and photosensitivity will be discussed. Also the EPR results at low temperature will be presented.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.