Structural, morphological, and luminescent properties of tetragonal-phase YPO₄:Eu³⁺

This work discusses the effect of europium concentration into YPO₄ structure and the structural, morphological, and luminescent properties of YPO₄:Eu³⁺ (2.5 mol%) powders synthesized by the hydrothermal method at pH = 2, 4.5, 6, and 9. The powders were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and luminescence spectroscopy. 5 and 10 mol% of europium promoted the hexagonal phase in YPO₄:Eu³⁺ powders synthesized at pH = 2. Rietveld refinements of the YPO₄:Eu³⁺ (2.5 mol%) powders crystallized in the tetragonal phase obtained at pH = 2, 4.5, 6, and 9 were addressed. YPO₄:Eu³⁺ powders synthesized at pH = 4.5 showed the highest luminescent intensity and the lowest electrical conductivity in the precursor solution. The lattice spacings of 4.551 and 3.435 Å for the powders synthesized at pH = 4.5 revealed the (101) and (200) reflections. All of the samples presented a high color purity, above 90%. The decay times of YPO₄:Eu³⁺ powders were 2.79, 2.86, 2.57, and 2.22 ms for the powders obtained at pH 2, 4.5, 6, and 9, respectively.