Improvement in thermal stability and temperature dependence of diffractivity in low-Tg photorefractive polymers dispersed with plasticizers

In the study to solve on the thermal instability due to the crystallization of additives for poly-N-vinylcarbazole (PVK)-based low-T-g photorefractive polymers with ethylcarbazole (EtCz) as a plasticizer, it has been found that the addition of a dimeric analog of PVK, 1,3-biscarbazolyl propane (BisCzPro), is very effective, and the replacement of EtCz with BisCzPro or EtCz/ BisCzPro mixtures enables us to control glass transition temperature (T-g) by changing the amount ratio of the additives and examine the temperature dependence of diffractivity while maintaining a transparent uniform film at high temperatures. As a result, we have clearly observed the existence of a specific temperature showing a maximum diffractivity, which is presumed to have resulted the decrease in the space field due to the detrapping and recombination of space charges by thermal agitation.