Radioluminescence(RL) behaviour of erbium-doped yttria nanoparticles(Y_2O_3:Er~(3+) NPs) which were produced by sol–gel method was reported for future scintillator applications. NPs with dopant rates of 1 at%, 5 at%, 10 at% and 20 at% Er were produced and calcined at 800°C, and effect of increased calcination temperature(1100°C) on the RL behaviour was also reported. X-ray diffraction(XRD) results showed that all phosphors had the cubic Y_2O_3 bixbyite-type structure. The lattice parameters, crystallite sizes(CS), and lattice strain values were calculated by Cohen-Wagner(C-W) and Williamson-Hall(W-H) methods, respectively. Additionally, the optimum solubility value of the Er~(3+) dopant ion in the Y_2O_3 host lattice was calculated to be approximately 4 at% according to Vegard's law, which was experimentally obtained from the 5 at% Er~(3+) ion containing solution. Both peak shifts in XRD patterns and X-ray photoelectron spectroscopy(XPS) analyses confirmed that Er~(3+) dopant ions were successfully incorporated into the Y_2O_3 host structure. High-resolution transmission electron microscopy(HRTEM) results verified the average CS values and agglomerated NPs morphologies were revealed. Scanning electron microscopy(SEM)results showed the neck formation between the particles due to increased calcination temperature. As a result of the RL measurements under a Cu Kα X-ray radiation(wavelength, λ = 0.154 nm) source with 50 kV and 10 mA beam current, it was determined that the highest RL emission belonged to 5 at% Er doped sample. In the RL emission spectrum, the emission peaks were observed in the wavelength ranges of 510–575 nm(~2H_(11/2), ~4S_(3/2)–~4I_(15/2); green emission) and 645–690 nm(~4F_(9/2)–~4I_(15/2); red emission). The emission peaks at 581, 583, 587, 593, 601, 611 and 632 nm wavelengths were also detected. It was found that both dopant rate and calcination temperature affected the RL emission intensity. The color shifted from red to green with increasing calcination temperature which was attributed to the increased crystallinity and reduced crystal defects.