187 SEMICONDUCTOR-DOPED POLYMERS. LINEAR AND NONLINEAR OPTICAL PROPERTIES. Y. Wang, A. Suna, and W. Mahler E. I. du Pont de Nemours and Company, Central Research and Development Department, Experimental Station, Wilmington, DE 19898 ABSTRACT: Semiconductor clusters with sizes of a few to hundreds of A, covering the entire range from molecular to bulk, have been prepared within polymer films. For PbS, the band-gap shifts to higher energy as the cluster size decreases and eventually converges to the transition energy of the first excited state of PbS molecule. The observed dependence of band-gap on cluster size can be explained by a tight- binding model that takes into account the effects of band nonparabolicity. These semiconductor-doped polymers represent a new class of nonlinear optical materials. Here we present the nonlinear optical properties of polymer films doped with 50 A CdS and discuss the possible mechanisms. INTRODUCTION: In this paper we discuss a new class of nonlinear optical materials, semiconductor-doped polymers. These materials are interesting for two reasons. First, the size of the semicondutor clusters can be controlled to vary from a few to hundreds of A. This provides a vehicle to study the transition of a semiconductor from molecular to bulk[1]. Secondly, by doping polymers with these small semiconductor clusters, utilizing their large (resonant) third order nonlinearity, new optically nonlinear composite materials can be prepared[2]. The dopants, semiconductor clusters, in essence "activate" the polymers. At present, this is probably the most general way to obtain optically nonlinear organic polymers. These semiconductor composites can have many advantages, other than the typical ones associated with polymers such as processing flexibility, mechanical stability .... etc. The speed of the nonlinearity can be much faster than bulk semiconductors since the presence of a high density of surface can shorten the carrier lifetime, which frequently dominates the nonlinearity of bulk semiconductors through the effects of band filling, bandgap renormalization,and screening of excitions[3,4]. Wavelength tuning can also be conveniently achieved by controlling the size and concentration of the semiconductor clusters. In addition, the nonlinearity of quantum-confined semiconductor particles, sometimes referred to as 'quantum dots', may be enhanced compared to bulk Mat. Res. Soc. Symp. Proc. Vol. 109. 1•988 Materials Research Society