CdSe/CdS core/shell quantum dots as sensitizer of a photorefractive polymer composite

CdSe/CdS core/shell, tri-n-octylphosphine oxide passivated, quantum dots are used to sensitize photorefractive polymer composite. The composite also consists of poly(N-vinylcarbazole) as the nominally charge transporting matrix and an electro-optic chromophore. The efficacy of sensitization and consequent photorefractive performance is investigated using transmission spectroscopy and ellipsometry, two-beam coupling and degenerate four-wave mixing experiments. The photorefractive nature of the photoinduced grating is confirmed by the observation of asymmetric two-beam coupling. Four-wave mixing reveals record diffraction efficiencies for nanoparticle-sensitized photorefractive polymer at the field levels applied (1.3% at 70 V. m 1). A recently developed analytical technique is used to extract space-charge field rise time values from degenerate four-wave mixing transients. In turn, analysis of the dependence of the rise time on applied field is used to determine the zero-field charge dissociation efficiency to be 3.6 x 10(-5) +/- 0.5 x 10(-5). It is further shown that the magnitude of this parameter accounts for most of the difference in photorefractive response rate between the present material and similar C-60 sensitized composite.