Synthesis of CdSeS Nanocrystals in Coordinating and Noncoordinating Solvents:  Solvent's Role in Evolution of the Optical and Structural Properties

CdSe x S y nanocrystals were synthesized in eight solvents that have different coordinating properties, trioctylphosphine oxide, trioctylphosphine, triphenylphosphine, oleylamine, hexadecylamine, dioctylamine, trioctylamine, and 1-octadecene at 230−300 °C. These nanocrystals exhibited high photoluminescence, which could be tuned over most of the visible region by changing the Se/S ratio or the solvent. The nanocrystals were characterized using UV−vis and IR spectroscopy, TEM, EDS, XRD, and NMR. 31P NMR and IR studies provided vital information about the nanocrystal surface capping ligands, indicating that those prepared in noncoordinating solvents were stabilized in solution mainly by oleic acid while those prepared in the coordinating solvents were stabilized mainly by solvent, phosphine and phosphine sulfide ligands, and some oleic acid. The hexagonal or cubic phase of these nanocrystals can be selectively prepared at temperatures as high as 300 °C by choosing the appropriate solvent.