Many studies have concentrated on exploring behaviors of nickel silver oxide nanoparticles using various routes of fabrication. Thermal treatment technique has never been utilized to fabricate nickel oxide silver oxide nanoparticles. In this research, binary (NiO)0.4 (Ag2O)0.6 nanoparticles were synthesized using the thermal treatment method due to its attractive advantages such as low cost, eco-friendly, and purity of nanoparticles. The structural, morphological, and optical behaviors of these nanoparticles were investigated at different calcined temperatures. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–Vis), and photoluminescence (PL) were the techniques used to characterize the synthesized nanoparticles. XRD was conducted at different calcined temperatures. The crystallite size was increased from 25.4 nm to 37.0 nm as the calcined temperature increased from 500 °C to 800 °C. Also, TEM results verified that the mean particle size was enlarged as the calcined temperatures increased. Two band gaps were found for each temperature, which were decreased from (3.05, 2.45) to (2.70, 1.95) eV as the temperature varied from 500 to 800 °C, respectively. Broadbands were observed by PL spectra, and the intensity of two emission peaks was also increased at higher temperatures. The results approved the successful formation of binary (NiO)0.4 (Ag2O)0.6 nanoparticles by a novel facile synthesis route. These nanoparticles are likely to have various applications, especially optical applications due to the formation of two band gaps.