Size-Selected Zinc Sulfide Nanocrystallites:  Synthesis, Structure, and Optical Studies

We report the synthesis of three sizes of thioglycerol-capped precipitated ZnS nanocrystallites with relatively narrow size distributions, having average sizes of 1.8, 2.5, and 3.5 nm, respectively. These crystallites were extracted as free-standing powders which remain stable under normal atmospheric conditions and can be redispersed in suitable solvents. The nanocrystallite powders were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), energy dispersive analysis of X-rays (EDAX), and UV−vis optical absorption. The synthesized nanocrystallites show typical lattice spacings corresponding to the cubic phase of ZnS, as confirmed from HRTEM, ED, and XRD. The lattice-resolved structures within a single nanocrystallite show characteristic defects such as twinning and dislocations. We present a comparative analysis of the size of nanocrystallites obtained from X-ray diffraction and TEM. The position of the excitonic transitions as seen in the optical absorption spectrum of the nanocrystallites was compared with the predictions of various models that correlate the size versus band gap of these nanocrystallites.