Semiconductor clusters in the sol-gel process: synthesis and properties of CdS nanocomposites

CdS nanocomposites (CdS cluster sizes < 5 nm) were prepared via multifunctional inorganic-organic sol-gel processing. In CdS sols as precursors, the CdS clusters are carrying inorganic components as stabilizing centers, along with bifunctional ligands acting as inorganic and organic network formers. Hydrolysis and condensation produces an inorganic skeleton yielding viscous liquids useful to prepare films or monoliths. The final organic cross-linking at T < 100°C results in optically transparent materials. The nature of stabilizing centers and the starting synthesis conditions influence strongly the resulting electronic properties. Cd2+ complexed by mercapto compounds gives smaller cluster sizes with a narrower distribution than Cd2+ complexed with amine or carboxylate groups. Mercaptosilane-stabilized CdS clusters synthesized via cleavage of bis triethoxy silyl propyl tetrasulfides show an enhanced room temperature photoluminescence compared with similarly stabilized clusters prepared through H2S exposure.