The created copper selenide (Cu:Se) nanoparticles were used in experiments for detecting UV light and in gas sensors. This research prepared Cu:Se nanoparticles with different ratios of 1:9, 2:8, and 3:7 using an atmospheric pressure plasma jet technique. The study looked at the optical properties of Cu:Se nanoparticles using XRD analyses, which showed that adding more Se made the crystals larger. UV–visible spectroscopy and the calculation of band gap energy were performed. All ratios yielded high transmission values, ranging from 80% to 95%. The band gap energy was found to be 3.80 eV, 3.25 eV, and 4.17 eV for the Cu:Se ratios of 1:9, 2:8, and 3:7, respectively, which are typical and excellent values for semiconductors. The prepared Cu:Se nanoparticles demonstrated good optical properties. The optical absorbance of Cu:Se NPs is in order in the wide region of λ = 200 to 350 nm, which is suitable for UV absorbance materials.