The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ∼1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm–1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. These data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. In addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. The photoconductive characteristics of the composites used for this study will also be considered.

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Characteristic diffusion in a Lorentz Gas system and its extensions are typically described through a scale-free order parameter. The relative validity of possible order parameters for the diffusion of a thick tracer rod through spherical scatterers in two and three dimensions as a function of the rod length L and scatterer density ρ has been examined by simulation. We find that the often-used two-dimensional order parameter, ρL 2 , is accurate. However, its naive generalization to three dimensions, changing the exponent according to dimensionality, does not fit the observed results. A revised order parameter can be generated through a theory based on the behavior of the mean free path of the tracer. We find that this generalized order parameter captures the multidimensional diffusive behavior.