Stabilized response-time in a photorefractive polymer composite doped with a styrene chromophore and C/sub 60/

Summary form only given. The response times of photorefractive polymers have been reduced by an order of magnitude, to milliseconds, over the past two years. It is generally agreed that photoconductivity and not orientational dynamics are the chief obstacle to even faster materials. Photogeneration efficiency, which is of order 1% in many materials described to date, is therefore a critical area of research. C/sub 60/, for instance, is a good candidate to enhance photogeneration. It has been found, however, that chromophores with ionization potentials smaller than that of the transport manifold can stabilize a population of C/sub 60//sup -/ and it has even been suggested that a photorefractive grating may be written in the distribution of C/sub 60//sup -/ and C/sub 60/. The accumulation of C/sub 60//sup -/ has been documented to occur under simultaneous electrical bias and optical excitation. We report measurements that show that the build-up of C/sub 60//sup s/ accompanied by large increases in the response-time of index-modulation in transient-grating experiments. This observation suggests that the response-time may be stabilized by increasing the chromophore ionization potential, and we have experimentally confirmed this expectation.