Electro-optic properties of CdS embedded in a polymer.

Abstract

CdS microcrystals under weak confinement conditions embedded in a polyvinyl alcohol polymer film have been optically characterized by linear absorption and time-resolved luminescence spectroscopy. They are studied in the presence of an external electrical field at low and room temperature and different densities of photoexcited carriers. By applying a voltage of 400 V corresponding to an external electric-field strength of 5\ifmmode\times\else\texttimes\fi{}${10}^{4}$ V/cm, the observed absorption change in this material is \ensuremath{\Delta}\ensuremath{\alpha}/\ensuremath{\alpha}\ensuremath{\approxeq}0.07. The electrical field produces a redshift of the absorption band which is explained in terms of the quantum-confined Stark effect. In addition, a restoring of the oscillator strength is observed and explained by screening effects of internal fields in the interface region by the photogenerated electron-hole pairs. At high laser excitation an electric-field-induced change of the nonlinear absorption spectrum of \ensuremath{\Delta}\ensuremath{\alpha}/\ensuremath{\alpha}=0.25 is achieved, giving a considerable modulation of the absorption edge. The electrical field separates the laser excited carriers and the change in the absorption is attributed to a compensation of the many-particle interaction by the external electrical field.