Size Quantization in Small Colloidal CdS Particles Studied with Stopped Flow Spectrometry

Size quantization effects have been observed in small particle size colloids (< 5 nm). Stopped-flow techniques have been used to observe the early stages of particle growth. Structure in the absorption spectra, which are believed to be due to quantization effects, have been detected in the first millisecond to 2.5 s of colloid formation. The structured spectra could be resolved into a series of Gaussian peaks of constant linewidth. The energy of the absorption maxima correspond surprisingly well to the predicted optical transitions for the theoretical model of carrier motion confined to a sphere of finite potential. The selection rules for optical transitions are found to be Δn = 0, Δl, ±1, ±2,... It was also found that the presence of different colloidal stabilizers leads to different modes of particle growth which can be explained with electrostatic and topological arguments.