Using different ratios of glycine to citric acid as fuel mixture in microwave-assisted combustion synthesis of Eu-doped Y₂O₃–Gd₂O₃ nanophosphors

Y₂O₃–Gd₂O₃:Eu nanophosphors were synthesized by the commercial combustion method in the microwave oven by using different fuel mixtures of glycine and citric acid in one-step processing with no post-heat treatment. Crystal structure and phase formation of samples were examined by X-ray diffraction (XRD) method. By increasing the concentration of citric acid in the fuel mixture to 25% (citric acid to glycine ratio of 1:3), more amorphous phases were crystallized, leading to a shift in the peak position to higher 2θ values. Transmission electron microscopy (TEM) showed nanoparticles with sizes less than 30 nm. The photoluminescence (PL) properties of the nanophosphors were also investigated under UV radiation (λ_ex = 254 nm). The major transition peaks at 590 and 614 nm were attributed to ⁵D₀ → ⁷F₁ magnetic dipole transition and ⁵D₀ → ⁷F₂ electric dipole transition, respectively. Fourier transform infrared (FTIR) curves showed absorption bands at 496, 557, and 809 cm⁻¹ due to the vibration of Gd–O, Y–O, and Eu–O bonds. Raman spectra of the nanophosphors showed a main peak at 358 cm⁻¹ for the rare-earth oxides. In addition to studying the fuel mixture, the charge transfer mechanism in the triple structure of Y³⁺, Gd³⁺, and Eu³⁺ with combined quantum-cutting phenomena is also discussed in this work for the first time. Crystallinity, homogeneity, and luminescence intensity of final products were optimized by using different glycine and citric acid fuel mixtures to control the rate of combustion. Hence, they are expected to provide a wide intense red emission for biological fluorescent labeling, high-resolution display applications, and UV-LED phosphors.