ELECTROOPTIC PROPERTIES OF CDS EMBEDDED IN A POLYMER

CdS microcrystals under weak confinement conditions embedded in a poly vinyl alcohol polymer film have been optically characterized by linear absorption and time-resolved luminescence spectroscopy. They are stud ied in the presence of an external electrical field at low and room te mperature and different densities of photoexcited carriers. By applyin g a voltage of 400 V corresponding to an external electric-field stren gth of 5 X 10(4) V/cm, the observed absorption change in this material is DELTAalpha/alpha almost-equal-to 0. 07. The electrical field produ ces a redshift of the absorption band which is explained in terms of t he quantum-confined Stark effect. In addition, a restoring of the osci llator strength is observed and explained by screening effects of inte rnal fields in the interface region by the photogenerated electron-hol e pairs. At high laser excitation an electric-field-induced change of the nonlinear absorption spectrum of DELTAalpha/alpha = 0.25 is achiev ed, giving a considerable modulation of the absorption edge. The elect rical field separates the laser excited carriers and the change in the absorption is attributed to a compensation of the many-particle inter action by the external electrical field.