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 aver age sizes of 1.8, 2.5, and 3.5 nm, respectively. These crystallites were ex tracted as free-standing powders which remain stable under normal atmospher ic conditions and can be redispersed in suitable solvents. The nanocrystall ite powders were characterized using X-ray diffraction (XRD), high-resoluti on transmission electron microscopy (HRTEM), electron diffraction (ED), ene rgy dispersive analysis of X-rays (EDAX), and UV-vis optical absorption. Th e synthesized nanocrystallites show typical lattice spacings corresponding to the cubic phase of ZnS, as confirmed from HRTEM, ED, and XRD. The lattic e-resolved structures within a single nanocrystallite show characteristic d efects such as twinning and dislocations. We present a comparative analysis of the size of nanocrystallites obtained from X-ray diffraction and TEM. T he position of the excitonic transitions as seen in the optical absorption spectrum of the nanocrystallites was compared with the predictions of vario us models that correlate the size versus band gap of these nanocrystallites .