<p>In this research, pristine zinc selenide nanoparticles (PZSNP), nickel (Ni)-doped zinc selenide nanoparticles (NDZSNP), and annealed zinc selenide nanoparticles (AZSNP) were prepared through a cost-effective solvothermal method. The influences of Ni doping concentration (DC) and annealing temperature (AT) on surface morphology, elemental, structural, and optical properties of PZSNP were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and UV–visible spectroscopy, respectively. The SEM images demonstrated that the particle size increased for NDZSNP and AZSNP in comparison to PZSNP. The EDX analysis displayed the existence of Zn, Se, and Ni atoms in the synthesized samples. Three prominent peaks were observed in the XRD patterns corresponding to (111), (220), and (311) planes, indicating the single cubic phase formation of the samples except for 18% NDZSNP and 673&#xa0;K AZSNP. At a doping concentration up to 12% and annealing temperature up to 573&#xa0;K, the diffraction peak intensity reached a maximum, beyond which (at 18% DC and 673&#xa0;K AT) it decreased, likely due to lattice distortion and secondary phase formation at higher doping/temperatures. The structural parameters such as crystallite size, microstrain, and dislocation density were calculated. It is noted in the FTIR spectra that the absorption peaks around 664&#xa0;cm⁻¹ are assigned to Zn–Se stretching vibrations, confirming the formation of PZSNP. The absorbance of NDZSNP and AZSNP decreased as compared to PZSNP. With increasing DC and AT, the direct optical band gap energy of PZSNP increased up to a certain limit, after that it decreased. These findings demonstrate that Ni-doping and annealing are effective strategies for tuning the structural and optical properties of ZSNP significantly, which could enhance their suitability for optoelectronic and photocatalytic applications.</p>