Rare-Earth-Doped Y₄Al₂O₉ Nanoparticles for Stable Light-Converting Phosphors

The ternary mixed metal oxides with high specific surface area are industrially important for sensors, catalysis, energy storage, and optoelectronics. However, synthesis of such metal oxides is always challenging, especially when multicomponent mixtures occur due to very narrow formation temperature windows. Flame spray pyrolysis is one of the best known techniques which enable formation of pure phases optimizing the temperature profile via control over the fuel/oxidizer ratio. Here, Y4Al2O9 (monoclinic phase of yttrium aluminum oxide, also known as YAM) and Y4–xEuxAl2O9 (x = 0.05–1.0) were strategically synthesized with specific precursor–solvent chemistry. While the hydrated yttrium nitrate with 28.2% water was unsuitable for the formation of crystalline Y4Al2O9 particles, the use of organic precursor–solvent combinations (Y/Al 2:1) resulted in 16 nm phase pure, highly crystalline Y4Al2O9 particles. All the materials were characterized by using X-ray diffraction with Rietveld refinement, Raman spectroscopy, and transmission electron microscopy. To develop a stable light-converting phosphor, the Y4Al2O9 host was doped with Eu to investigate the photoluminescence properties of Y4–xEuxAl2O9 (x = 0.05–1.0). The results indicated increased photoluminescence intensity with increasing Eu3+ concentration up to x = 0.5, i.e., Y3.5Eu0.5Al2O9, and a subsequent drop or decrease in intensity for x ≥ 0.7. Hence, Y3.5Eu0.5Al2O9 is proposed for a potential light-converting phosphor.