Structural, optical, and electronic properties of non-stoichiometric nano-ZnS_1−x: Mn_x

Non-stoichiometric ZnS_1−x:Mn_x nanomaterials were prepared using a thermolysis procedure by decreasing the stoichiometric amount of thiourea relative to the amount of zinc acetate as starting precursors: Zn(Ac)/(1−x) thiourea in the presence of (x) manganese acetate (x = 0, 0.01, 0.03, 0.05, and 0.1). Rietveld X-ray diffraction analysis was used to examine the structural modification in the ZnS lattice induced by sulfur deficiency and Mn²⁺ incorporation. The samples with x ≤ 0.01 exhibited a single ZnS zincblende phase, while other samples, x ≥ 0.02, have two phases ZnS and ZnO with different percentages. The lattice parameter of the system is governed by the Mn and S amounts in the matrix. A high-resolution transmission electron microscope established the quantum dot nature of the system. Fourier-transform infrared technique confirmed the presence of ZnS and ZnO phases in higher Mn-doped ZnS samples. The bandgap obtained from UV–vis analysis showed non-monotonic dependence on Mn content; it initially decreased and then increased to form a bandgap “bowing.” Photoluminescence analysis revealed that the emission colors depended on the amount of Mn doping in the matrix. The PL intensity raised for all Mn-doped samples as compared with the pristine sample reached its maximum value for the 3% and 5% Mn samples. The PL exhibited a red shift for the high dopant amount of Mn. Density function theory calculation was used to explore the electronic and optical characteristics of pure phases in ZnS_1−xMn_x system.