Over the past few years, there has been a significant focus on studying the synthesis and applications of metal nanoparticles. These tiny particles possess distinct properties that set them apart from bulk metals. The liquid for Cr:Se core-shell nanoparticles was made using the plasma jets method and turned into thin films that are 158.9 nm thick through chemical spray pyrolysis. The nanothin films were analyzed using X-ray diffraction (XRD), ultraviolet-visible spectroscopy, and transmission electron microscopy (TEM). This study looks at the structure and light properties of core-shell nanoparticles made with a chromium to selenium (Cr:Se) ratio of 6:4. The XRD patterns confirmed the crystalline nature of the nanoparticles for the polycrystalline ratio (6:4). When the best thin film, which is well-crystallized, is exposed to non-thermal plasma (dielectric barrier discharges (DBD)), the XRD shows important changes, suggesting it is becoming more crystalline. Tauc plots show that the direct bandgap energies change in a non-linear way, with a notable increase in energy from 2.77 to 3.88 eV. Transmission electron microscopy analysis highlights improved nanoparticle distribution and uniformity. These findings point out the importance of Cr:Se nanoparticles for advanced optoelectronic and sensing technologies, as well as various technological applications.