MnSb-Based Quantum Dots: Defect-Mediated Photoluminescence in Multiphase Nanostructures via Green Colloidal Synthesis

MnSb-based quantum dots are an emerging class of lead-free luminescent nanomaterials with potential for sustainable photonic applications. In this work, defect-emissive Mn-Sb/MnOx quantum nanostructures were synthesized via a green ethanol-assisted colloidal reflux method using oleic acid as a surface-passivating ligand under an inert nitrogen atmosphere. The synthesized nanostructures exhibited an average particle size of ∼5.3 nm with good colloidal dispersibility and narrow size distribution. Structural characterization by XRD, TEM, SAED, XRF, Raman spectroscopy, and XPS collectively suggests the formation of Mn-Sb-related nanocrystalline domains embedded within MnOx-rich surface environments, indicating a structurally heterogeneous and defect-rich nanoscale system. Optical measurements showed a pronounced absorption feature near 230 nm and effective optical transition energies of 3.9-4.1 eV. Because the synthesized material is structurally heterogeneous and contains MnOx-rich surface environments, the estimated optical transition energies should be regarded as effective optical transition energies rather than a true semiconductor band gap. Broad green photoluminescence centered at 518-525 nm was observed, with a maximum photoluminescence quantum yield (PLQY) of 62.3%. The emission is attributed to defect-mediated and interface-assisted radiative recombination associated with Mn-Sb-related nanodomains, MnOx-rich surface species, and ligand-passivated defect states. These findings demonstrate that defect engineering in MnSb-based multiphase quantum dots provides an effective strategy for designing efficient lead-free luminescent nanomaterials.