Effects of dopant rate and calcination parameters on photoluminescence emission of Y₂O₃:Eu³⁺ phosphors: A statistical approach

In this study, Y₂O₃:Eu³⁺ phosphorescent powders with different dopant rates were synthesized by sol-gel method. Statistical experimental design methods were used to investigate the effects of calcination temperature (800, 900 and 1200 °C), time (5 and 7 h) and dopant rate (5 and 7% at.) on the colour of the photoluminescence emission. The XRD results showed that as-prepared powders were amorphous. After calcination, the crystal structures became cubic bixbyite-type. XRD and Raman spectroscopy results confirmed the existence of Eu³⁺ in the Y₂O₃ crystal. Crystallite sizes and lattice parameters of the powders were calculated by using Williamson-Hall and Cohen-Wagner methods, respectively. Photoluminescence emission spectra of the samples were measured at room temperature by using an optical emission spectroscope with 380 nm monochromatic excitation source and the emission spectra were transformed to CIELab colour space coordinates. The emission spectra exhibited a strong characteristic peak at 611 nm and a smaller peak at 614 nm. Depending on the dopant rate and the calcination parameters, other smaller peaks appeared at 587, 592, 606, 623 and 631 nm. The CIELab colour space transformation results showed that the powders possessed orange-red emission. The dopant rate and the calcination conditions slightly changed the emission colour. According to the statistical analysis, the dopant rate had the strongest effect on a* colour space value (redness) whereas all parameters had equally significant effect on b* colour space value (yellowness). The ANOVA analysis revealed that the interaction between the temperature and the dopant rate was also statistically significant with the confidence level of 95%. This interaction was attributed to the relation between lattice strain and calcination temperature, which confirms the strong symmetry dependence of the electron-dipole (ED) transitions of the Y₂O₃:Eu³⁺ phosphors.