Linear-, nonlinear-, and electro-optic properties of CdS nanocrystals embedded in a polymer

A review about the linear-, nonlinear-, and electro-optic properties of CdS nanocrystals embedded in films of polyvinyl- alcohol (PVA) are given. The preparation of CdS crystals using a polymer matrix is shown to be an alternative method to produce 3D-quantum confined structures, instead of, e.g., the usual growth in glasses. To characterize the optical properties, degenerate four-wave mixing and absorption-saturation experiments have been carried out. Additionally, the electric field-induced absorption change has been measured at different laser excitation intensities. Comparing different glass matrizes with the polymer, the nonlinear-optical experiments show a considerable decrease in the bleaching efficiency with increasing trap density. This behaviour can be explained by an additional term introduced into the two-level system representing the properties of the interface. The probability of localisation, capture, and transfer of carriers into the surrounding matrix rises with increasing density of traps in the interface region. This is in agreement with a theoretical model describing the probability to find an excited electron-hole pair near the interface.1 The measurements of degenerate four-wave mixing show an astonishing result if comparing the values of nonlinear susceptibility χ(3)- For the PVA-film the susceptibility is about twice the value of χ(3) reported for the experiments carried out at CdS-doped in glasses.