Influence of growth conditions on structural and optical properties of Eu3+doped yttrium/aluminum-based oxide powders obtained by the microwave-driven hydrothermal method.

In this study, we investigated the impact of growth conditions on the structural and optical properties of yttrium/aluminum-based oxide powders doped with Eu³⁺synthesized via microwave-driven hydrothermal method. The effects of the starting material composition (Y/Al molar ratio) and the pH value of the reaction medium on the phase composition, morphology, and luminescent properties of the Eu dopant in the obtained powders were analyzed. Detailed structural and optical characterization of material was performed using x-ray diffraction, scanning and transmission electron microscopy (SEM, TEM), and the results were confronted with the analysis of the photoluminescence (PL), PL decay kinetics, and PL excitation spectroscopy features, as the Eu dopant apart of being efficient red phosphor is also known as a good crystal symmetry probe. It has been shown that the pH value of the reaction mixture and the Y/Al molar ratio significantly affect the phase composition of the powders, morphology, size, and consequently, the intensity of emission peaks and decay times. Despite using the yttrium to aluminum ratios of 1:1 in one of the sample series, corresponding to YAlO₃perovskite, the presence of two other phases: yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) and yttrium oxide (Y₂O₃) in different proportions was observed. Additionally, TEM images demonstrated the presence of a non-crystalline phase in two samples which correlated with a significant broadening of PL lines. The analysis of the CIE diagrams revealed that a decrease in pH value causes the an increase of the red component of the obtained powder phosphor emission. The research provides new insights into the relationships between synthesis parameters and the physicochemical and optical properties of Eu³⁺-doped yttrium/aluminum-based oxide materials compounds, which is important for both optimizing the growth parameters to obtain desired Y-Al-O powder crystal phase and for the use of these powders in applications as phosphor materials.