Microwave-Assisted Synthesis and Investigation of Optical and Structural Properties of Pure and Mn

Pure and Mn2+-doped ZnS quantum dots (QDs) were synthesized using a rapid microwave-assisted method, and their structural, morphological, compositional, and optical properties were systematically investigated. X-ray diffraction confirmed the formation of single-phase cubic zinc blende ZnS with successful substitution of Mn2+ ions at Zn2+ lattice sites. The crystallite sizes remained below the exciton Bohr radius, indicating strong quantum confinement. FTIR analysis verified Zn-S bonding and Mn incorporation without impurity phases. FESEM revealed a morphology transformation from flower-like structures in pure ZnS to dense nanoparticle agglomerates with increasing Mn content. EDX confirmed compositional purity and controlled Mn substitution. Photoluminescence studies showed a near-band-edge excitation at 328 nm and dual emission behavior: blue emission (~491 nm) from intrinsic defects and orange-red emission (~662 nm) from Mn2+ intra-ionic transitions. While blue emission intensity decreased with Mn doping due to non-radiative recombination centers, the Mn-related orange-red emission remained stable, indicating saturation of luminescent Mn centers. The tunable optical properties, stable dopant incorporation, and strong quantum confinement make Mn-doped ZnS QDs promising candidates for optoelectronic, photonic, and luminescent applications.