<p>Mn²⁺-, Ni²⁺-, and Co³⁺-doped pyrrhotite nanoparticles were synthesized via the hot injection thermolysis method. The optical and structural properties of the pure and doped pyrrhotite nanoparticles were studied using UV–visible spectroscopy. Powder X-ray diffractometry (p-XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize the particles. p-XRD studies showed that doping had no effect on the basic structure of the nanoparticles. The doped nanoparticles showed the formation of single-phase monoclinic type pyrrhotite (Fe_1-xS) structure. UV–visible spectroscopy revealed that the incorporation of Ni²⁺, Fe³⁺, and Co³⁺ ions as dopants decreases the energy bandgap of the pyrrhotite nanoparticles. TEM images showed an increase in nanoparticle sizes with the incorporation of dopants. Both elemental mapping and EDX analysis of the doped nanoparticles reveal the presence of Mn²⁺, Ni²⁺, and Co³⁺ doping ions in the pyrrhotite lattice.</p> Graphical abstract <p></p>