Effect of Mg and Cu doping on structural, optical, electronic, and thermal properties of ZnS quantum dots

Undoped and 10% Mg or Cu-doped ZnS quantum dots (Zn_0.9Mg_0.1S and Zn_0.9Cu_0.1S) were prepared by a simple chemical method at low temperature (300 °C). The effect of doping on structural characteristics was investigated using Rietveld profile method and the high-resolution transmission electron microscope techniques. Differential scanning calorimetry (DSC) scans were recorded in the temperature range 23–600 °C with different heating rates (5 to 30 °C/min). The model-free isoconversional method was applied to explore the effect of doping on the reaction and the growth mechanism of nano-ZnS. Diffuse UV reflectance revealed an increase of the optical energy gap upon doping with Mg, while it decreased as ZnS was doped with Cu. The change in energy gap upon doping was explained using density function theory calculation. The photoluminescence (PL) spectra revealed violet, blue, green colors depended on the composition and excitation wavelength used in the study. The intensity of PL has been increased for doped samples compared with pristine ZnS. Tuning the energy gap of ZnS through doping enable applications for light-harvesting and photocatalytic degradation in the visible region.