SYNTHESIS AND CHARACTERIZATION OF SURFACE-MODIFIED COLLOIDAL CDTE QUANTUM DOTS

The controlled synthesis of quantized colloidal CdTe nanocrystals (in aqueous solutions) with narrow size distributions and stabilized again st rapid oxidation was achieved by capping the quantum dot particles w ith 3-mercapto-1,2-propanediol. Nanocrystals (i.e., quantum dots) with mean diameters of 20, 25, 35, and 40 Angstrom were produced. Optical absorption spectra showed strong excitonic peaks at the smallest size; the absorption coefficient was shown to follow an inverse cube depend ence on particle diameter, while the extinction coefficient per partic le remained constant. The quantum yield for photoluminescence increase d with decreasing particle size and reached 20% at 20 Angstrom. The va lence band edges of the CdTe quantum dots were determined by pulse rad iolysis experiments (hole injection from oxidizing radicals); the band gaps were estimated from pulse radiolysis data (redox potentials of ho le and electron injecting radicals) and from the optical spectra. The dependence of the CdTe bandgap on quantum dot size was found to be muc h weaker than predicted by the effective mass approximation; this resu lt is consistent with recently published theoretical calculations by s everal groups.