A new rare-earth borate Sr3Dy2(BO3)4 and tunable luminescence properties of Sr3Dy2-2xEu2x(BO3)4 phosphors

Abstract

A new rare-earth borate Sr₃Dy₂(BO₃)₄ was obtained by high-temperature solution reaction at 950 °C and structurally characterized by single-crystal XRD for the first time. It crystallizes in the orthorhombic system (Pnma group, Z = 12) with cell parameters of a = 22.2265(3) Å, b = 15.8861(2) Å, c = 8.7096(1) Å, V = 3075.29(7) ų. The compound features a complex 3D framework constructed by (Dy/Sr)O_n (n = 7, 8, and 9) polyhedra and BO₃ planar triangles. Moreover, solid solutions of Sr₃Dy_2-2xEu_2x(BO₃)₄ (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction route. The obtained products were characterized by powder XRD/Rietveld refinement, SEM/EDS, IR/Raman, XPS, DRS, and photoluminescence techniques. It was found that all samples were in the yellow-white light region under excitation at 351 nm. Among them, Sr₃Dy_1.6Eu_0.4(BO₃)₄ exhibits the CIE coordinates of (0.3292, 0.3536), close to the standard white-light illumination. When λ_ex = 394 nm, as the Eu³⁺ content varies from x = 0 to 0.2, the emission color of Sr₃Dy_2-2xEu_2x(BO₃)₄ can be adjusted from yellow-white (0.3280, 0.3834) to yellow-pink (0.5373, 0.3667). Thus, color-tunable and white emissions can be achieved by controlling the wavelength of the excitation light and the Eu³⁺/Dy³⁺ ratio. Meanwhile, the temperature-dependent analysis of Sr₃Dy_1.6Eu_0.4(BO₃)₄ proved the high thermal stability, with the emission intensity at 150 °C remaining >75 % of its value at room temperature. These results indicate that Sr₃Dy_2-2xEu_2x(BO₃)₄ has the potential as a single-phase white-emitting phosphor for w-LED applications.