Cubic-to-hexagonal phase transition and optical properties of chemically synthesized ZnS nanocrystals

Cubic phase of ZnS nanocrystals, having particle size of 1.1–1.5 nm, is synthesized by the chemical co-precipitation method with different pH (4–12) of the reaction mixture. The nanostructures are characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–Visible spectrophotometry. As-synthesized ZnS samples are annealed for 2 h at different temperatures (Tc), determined from the differential scanning calorimetry (DSC) study. The phase-transformation (∼25%) from cubic to hexagonal phase of ZnS has been observed at very low temperatures at ∼250 °C. Enhanced photoluminescence (PL) emissions are observed in the annealed samples as well as in the samples synthesized with higher pH values.