Synthesis and Optical Properties of Cadmium- and Lead-Chalcogenide Semiconductor Clusters (Diameter < 5 Nm) In Liquid Solutions and Silicate Glasses

Abstract

ABSTRACTSmall-particle clusters of CdS, CdSe, CdTe, PbS, and PbSe have been synthesized in aqueous solution. Absorption spectra with very sharp maxima were obtained for extremely small clusters (diameters < 30 Å). However, when clusters grow the excitonic absorption bands gradually decrease and the sharp maxima are replaced by broad shoulders. Cadmium chalcogenide clusters capped with 3-mercapto-l, 2-propanediol can be collected as stable solids with the same properties as original clusters. A method for the incorporation of semiconductor clusters in transparent silicate glasses has been developed. This technique relies on the low temperature sol-gel process, and silane alkoxide as the starting material. The absorption spectra of the clusters in the glasses are identical to those of the starting aqueous solutions. Excess charge carriers on PbS and CdS clusters lead to a blue shift in the optical absorption edge of semiconductors. The appearance of this shift depends critically on the method of colloid preparation and surface chemistry.