Structure and Optical Properties of CdS Superclusters in Zeolite Hosts

摘要

Direct synthesis of Cadmium Sulfide within the pore structure of zeolites leads to a novel supercluster with a structural geometry superimposed by the host framework. Detailed X ray powder diffraction, EXAFS analysis and optical absorption data reveal discrete (CdS)4 cubes located within the small sodalite units of the structure which begin to interconnect as the loading density within the zeolite rises. The discrete cube building blocks consist of interlocking tetrahedra of Cd and S with a CdS bond length of 2.47A. At higher loadings these cubes begin to occupy adjacent sodalite units where the Cd atoms point toward each other through the double six-rings linking the sodalite moeities with a Cd-Cd distance of approx. 6A. As this three dimensional interconnection proceeds, the corresponding changes in optical properties indicate a transformation to a semiconductor supercluster with behavior intermediate between that of the discrete CdS cubes and bulk semiconductor. Semiconductor superclusters represent a novel class of materials where the 3-dimensional structure and electronic properties can be controlled by using different zeolites as the template. (mjm)