Understanding trapping in photorefractive polymer composites for optical processing applications

Summary form only given. The high gain and index modulation reported for several new photorefractive polymer composites may open the way for future applications of this promising class of materials for optical processing. In this work we focus on identification of the trapping states with a goal of eventual optimization of this critical component. We consider composites of the general composition PVK:NLO:BBP:C/sub 60/, where PVK is the photoconducting host poly(N-vinyl carbazole), NLO is a nonlinear optical chromophore of the form amino-dicyanostyrene, BBP is the liquid plasticizer butyl benzyl phthalate, and the fullerene C/sub 60/ sensitizes hole generation for red wavelengths near 650 nm. Since optical absorption by the fullerene produces mobile holes, the fullerene anion is formed in the process. We present evidence that the radical anion of C/sub 60/ acts as the primary photorefractive hole trap in C/sub 60/-sensitized photorefractive polymers, using the strong near-infrared absorption of C/sub 60/ to quantify the anion concentration in situ. The spectroscopically determined concentration correlates well with the photorefractive trap density obtained from analysis of the photorefractive performance.