CdSxSe1-x NANOCRYSTALLITES : NEW MATERIALS FOR NON LINEAR OPTICS

Abstract

Nanocrystallites of CdS,Sel-, semiconductors in glasses have non-linear propemes which are function of the exciton confinement due to their sizes. The determination of the diameter of these nanocrystallites , critical to improve the properties of the systems, is determined by Raman scattering close to the laser line : the Low Frequency Inelastic Scattering (LOFIS). Possibility to determine the size distribution by LOFIS is demonstrated and effects of thermal treatments on the sizes and the size distribution of is discussed. Mesoscopic systems , intermediate between the bulk material and the molecule , attracted recently much interest both from a fundamental point of view and for their potential applications for non-linear optics. Among them Cds~Sel-~ semiconductors in glasses are widely studied: nanocrystals with diameters smaller than the Bohr diameter of the exciton can be grown in the glassy mamx. Quantum confinement effects are then expected and non-linear optical properties are observed in these systems. Optical properties of 11-VI semiconductors nanocrystallites are known for many years as optical filter, the absorption edge being function of the sulfur content x.From the precursor of these filters nanocrystals with different sizes are easily obtained by controlled heat treatments.In this paper we will present briefly non- linear optical properties and focus then on a critical point for their improvement : the size dismbution of the nanocrystals in the glass.