Study of the luminescence mechanism of gadolinium and yttrium oxide hosts for Eu³⁺ rare earth ion synthesized by sol-gel method assisted with oleic acid

Yttrium and gadolinium oxides doped with Eu³⁺ ions were synthesized using the sol-gel method, which was assisted with oleic acid as a surface-directing agent. Their morphology and structure were characterized by X-ray diffraction and transmission electron microscopy. Yttrium oxide synthesized phosphors exhibited well-defined facets and good dispersion, while gadolinium oxide particles presented high coalescence. Moreover, all synthesized materials showed a cubic structure. A formation mechanism was proposed using the results of Fourier transform infrared spectroscopy, where the as-precipitated phosphors transformations from oxo-hydroxide to crystalline yttrium and gadolinium oxides were observed. In addition, a surface modification of particles was produced by the synthesis method. On the other hand, luminescence analyses showed a strong emission peak at 612 nm in both oxides, and it was found that gadolinium oxide was the most effective host for luminescence emission. This matrix required a smaller dopant content to reach its maximum luminescence emission and exhibited the highest theoretical quantum efficiency. Also, color purity was evaluated using the CIE 1931 coordinate system, where x coordinate was found to increase as a function of dopant content indicating a higher perception of red color for gadolinium oxide matrix. Finally, energy diagrams and rate equations were proposed to explain their energy transfer mechanisms.