Effect of composition ratio on the structural and optical properties of MnS@ZnS nanocomposites

Abstract

Nanocomposites (1−x)MnS‒xZnS (x = 0, 0.25, 0.5, 0.75, 1) heterostructures were synthesized by a simple chemical procedure at low temperature (300 °C). The influence of the alloying ratio (x) on the phases developed was investigated utilizing the Rietveld X-ray diffraction (XRD) analysis and Fourier transform infrared (FTIR). Zinc sulfide crystallized in one phase having zincblende structure, while manganese sulfide was formed in three phases having cubic and hexagonal structures. The determined crystallite size for ZnS was in the range 3–4 nm, resembling quantum dots, while for the cubic MnS phase the size was bigger in the range 15–20 nm, and it is much bigger for MnS hexagonal phase, about 76 nm. A High-resolution transmission electron microscope (HRTEM) images confirmed the big difference in particle sizes of MnS and ZnS. The UV diffused reflectance was obviously affected by the ratio of MnS to ZnS in the matrix; the intermediate composites (0.25, 0.5, and 0.75) had bandgap energy less than those of pure MnS and ZnS. The refractive index value was influenced by the degree of crystallinity and density of the samples. Photoluminescence (PL) analysis revealed high dependence on the sample composition with ZnS and the intermediate composites samples had broader spectra compared to the MnS sample; the intermediate samples were blue shifted. Also, PL intensities of intermediate nanocomposites were less than those of MnS and ZnS samples.