Crystallographic, Structural and Band Gap Tailoring of Zn0.98Mn0.02S Quantum Dots Co-Doped with Cu by Co-Precipitation Method

Zn0.98-xCuxMn0.02S (x = 0, 0.02, 0.04) quantum dots with different Cu concentrations have been successfully synthesized by co-precipitation method. Cubic phase exhibited in Zn0.98Mn0.02S turned to mixture of both cubic and hexagonal phases by Cu-doping which was confirmed by X-ray diffraction pattern. The shift of peak position along (111) plane and the diminishing of interplanar distance and lattice constant confirmed the proper substitution of Cu and Mn in ZnS. Cubic phase of ZnS was tuned towards hexagonal phase by Cu-doping i.e., morphology diminishes stability which was confirmed by microscopic images. Optical studies revealed the wide tuning of band gap between 3.3 and 3.93 eV by Mn-doping and Cu co-doping which is useful for opto-electronic device applications. Photoluminescence spectra illustrated two distinct emission bands, UV emission around 392-396 nm and defect related blue emission around 470-481 nm. The change in intensity and peak position of UV and blue emission was discussed based on crystallite size formation of defect states by Cu-doping.