Influence of composition on the photoconductive and photorefractive properties of PVK composites

We present a theoretical and experimental study of both photoconductivity and photorefraction (PR) in several PVK- based photorefractive composites. We used the modified Schildkraut and Buettner's model of space-charge formation in photorefractive polymers that includes both deep and shallow traps. The dynamic equations have been solved semi- empirically using independent measurements of photoconductive properties to predict photorefractive dynamics. Dependence of the dynamics on charge generation, mobility, trap density, acceptor density, ionized acceptor density, as well as their associated rates is examined. The magnitude of the fast time constant of photorefractive development is successfully predicted. The model has also been found to qualitatively predict the reduction in speed due to deep trap filling and ionized acceptor growth. By choosing chromophores with different ionization potentials and by varying the chromophore concentrations, we study the influence of the chromophore ionization potential on the photoelectric and PR properties and reveal the nature of deep traps in the composites and their contribution to both photoconductivity and PR dynamics. Effects of plasticizer components were also investigated.

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