Synthesis of SnO₂ and ZnO Colloidal Nanocrystals from the Decomposition of Tin(II) 2-Ethylhexanoate and Zinc(II) 2-Ethylhexanoate

We report for the first time the nonhydrolytic synthesis of soluble SnO₂ nanocrystals, by the decomposition at temperatures between 230 and 250 °C of tin(II) 2-ethylhexanoate in diphenyl ether and in the presence of amines as surface capping agents. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) studies showed that highly crystalline nanoparticles were obtained with a mean size ranging from about 3 to about 3.5 nm, depending on the length of the alkyl chain of the amine. The use of metal 2-ethylhexanoate in the synthesis of oxide nanocrystals was generalized by preparing ZnO nanocrystals from the decomposition under similar conditions of zinc(II) 2-ethylhexanoate. In this case, soluble nanocrystals with a size ranging from about 5 to 8 nm were obtained. It is shown that the decomposition path of the precursor depends on the specific metal, and may result in the sudden formation of pyrolized products instead of soluble nanocrystals. The optical properties of capped SnO₂ nanocrystals are reported for the first time and are characterized by only a blue luminescence, while for the ZnO colloids the photoluminescence spectra are characterized by the typical band-edge and surface defects emission bands, but in these samples the latter band is unusually much weaker than the former.