Variation of cadmium sulfide nanoparticle size and photoluminescence intensity with altered aqueous synthesis conditions

Water-soluble cadmium sulfide (CdS) nanocrystal quantum dots were synthesized by aqueous-phase arrested precipitation in the presence of thiolate capping ligands. The relationship between the synthesis conditions and spectroscopic properties was studied. Several factors affect the absorbance and photoluminescence (PL) spectra, including reactant concentration, Cd:S mole ratios, reactant to ligand mole ratios, ligand length, pH, and ligand R group. Particle size increased with higher pH or sulfur concentration, yet particles approximately 2 nm in diameter exhibited maximum PL quantum yield regardless of synthesis conditions. The data support the idea that specific Cd-thiolate ligand complex formation modulates nanocrystal growth. These results illustrate the importance of intermediate metal-ligand complex formation to nanocrystal arrested precipitation growth kinetics, particle stabilization, and ultimately, their optical properties.