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

Abstract

CdSe/CdS core/shell, tri-n-octylphosphine oxide passivated, quantum dots are used to sensitize a 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 photo-induced grating is confirmed by the observation of asymmetric two-beam coupling. Four-wave mixing reveals record diffraction efficiencies for a nano-particle-sensitized photorefractive polymer at the field levels applied (1.3% at 70 V.μm−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 × 10−5 ± 0.5 × 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 a similar C60 sensitized composite.