Engineered nanostructures exhibiting enhanced optical nonlinearity

Because of their unique chemical and physical properties, nanometer-sized semiconductor materials have attracted broad attention in the fields of physics, chemistry, and biology. These capabilities are mainly due to the unusual dependence of the electronic and optical properties on quantum confinement, which for semiconductor materials restricts the particle size in the 1 to 10 nm range. We have fabricated and measured novel nanostructures of semiconductor quantum dots capped with surfactants and embedded in organic thin films that exhibit several orders of magnitude increase in their multiphoton cross-sections of absorption relative to semiconductor quantum dots capped with surfactants in solution or in other matrix materials. Large values of optical nonlinearity have been measured for CdS and CdSe quantum dots in these engineered nanostructures. We will discuss these findings within the context of theoretically proposed hybrid excitons in organic-inorganic nanostructures.