Zinc blende and wurtzite cadmium sulfide nanocrystals with strong photoluminescence and ultrastability

A hydrothermal route to the production of high-quality CdS semiconductor nanocrystallites is presented. Water-soluble crystallites about 5 nm in diameter with zinc blende and wurtzite crystal structure, strong photoluminescence and strong stability are prepared. The synthesis is based on the separation of the nucleation and growth stages by controlling some crucial factors such as temperature, pH and concentration of reactant mixture. These measures provide temporally discrete nucleation and permit controlled growth of quantities of nanocrystallites. Zinc blende and wurtzite structural CdS nanocrystallites were both synthesized by using cadmium acetate, l-cysteine, 3-mercaptopropionic acid and thiourea as precursors, respectively. Ostwald ripening process under high temperature leads to high sample quality. CdS semiconductor nanocrystallites show sharp excitation features and strong “band-edge” emission which is maintained very strongly 10 months after precipitation. Transmission electron microscopy and X-ray powder diffraction indicate the presence of bulk structural properties in crystallites as small as 5 nm in diameter. Ultrastability and super strong photoluminescence emission of as-prepared CdS semiconductor nanocrystallites indicate its potential practical value.