Synthesis of size-tunable zinc blende ZnS nanocrystals

Quasi-polyhedral ZnS nanocrystals with monodisperse tunable sizes of 40, 52, 62, 73, 82, 94, 103, and 110 nm have been synthesized in aqueous solution by regulating the amounts of thioacetamide, zinc acetate, and acetic acid added. The mixture was heated to 120 degrees C in an oven for 10-20 min to produce the nanocrystals. Structural characterization reveals the formation of cubic zinc blende ZnS with some polycrystallinity, which possibly influences their optical properties, that is, the measured band gaps do not give a continuous narrowing trend with increasing particle size. However, when particle sizes are expressed in terms of volumes, the absorption band positions show steady red shifts with increasing crystal dimensions and very small wavelength changes for nanocrystals beyond 90 nm. Thus, these ZnS nanocrystals still possess some size-dependent optical properties despite their polycrystalline nature.