Synthesis, characterization and radioluminescence properties of erbium-doped yttria phosphors

In this paper, radioluminescence (RL) behaviour of erbium-doped yttria nanoparticles (Y₂O₃:Er³⁺ NPs) which were produced by sol-gel method is reported for future scintillator applications. NPs with dopant rate of 1, 5, 10 and 20 at. % Er were produced and calcined at 800°C, effects of increased calcination temperature on the RL behaviour (1100°C) was also reported. X-ray Diffraction (XRD) results showed that all phosphors had the cubic Y₂O₃ bixbyite-type structure. The lattice parameters, crystallite sizes 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 Er³⁺ dopant ion in the Y₂O₃ host lattice was calculated according to Vegard’s law to be approximately 4 at. %, which was experimentally obtained from the 5 at. % Er³⁺ ion containing solution. Both peak shifts in XRD patterns and X-Ray Photoelectron Spectroscopy (XPS) analyses confirmed that Er³⁺ dopant ions were successfully incorporated into the Y₂O₃ 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 K_α X-ray radiation (λ=0.154 nm) source with 50 kV and 10 mA beam current, it was determined that the highest RL emission belongs to 5 at. % Er doped sample. In the RL emission spectrum, the emission peaks were observed in the wavelength range 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 colour shifted from red to green with increasing calcination temperature which was attributed to the increased crystallinity and reduced crystal defects.