Two new rare-earth oxyborates Ba4BiTbO(BO3)4 and Ba1.54Sr2.46BiTbO(BO3)4 and luminescence properties of the Ba4BiTb1−xEuxO(BO3)4 phosphors

Abstract

Single crystals of two new terbium oxyborates Ba₄BiTbO(BO₃)₄ and Ba_1.54Sr_2.46BiTbO(BO₃)₄ were obtained by the high-temperature solution method. They crystallize in the hexagonal P6₃/mmc group (Z = 2) with lattice parameters of a = 5.41865(9) Å, c = 26.3535(5) Å, V = 670.12(3) ų and a = 5.36534(19) Å, c = 26.0661(10) Å, V = 649.83(5) ų, respectively. Their crystal structures feature two kinds of layers: [Tb(BO₃)₂]_n³ⁿ⁻ formed by corner-sharing TbO₆ octahedra and BO₃ triangles, as well as [Bi(BO₃)₂O]_n⁵ⁿ⁻ consisting of Bi₂O₁₃ dimers and BO₃ groups, with alkali-earth cations sitting inside and between the layers. In addition, solid solutions of Ba₄BiTb_1−xEu_xO(BO₃)₄ (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction method. The obtained products were characterized by powder XRD, SEM, IR/Raman, XPS, DRS, and luminescence spectroscopy. It was found that as the Eu³⁺ doped content varies from x = 0 to 0.2, the emission color of the Ba₄BiTb_1−xEu_xO(BO₃)₄ phosphors can be adjusted from cyan to near-white and then to orange-red or from green to orange and then to red under the excitation of 349 and 377 nm, respectively. Furthermore, the emission intensities and chromaticity coordinates were found to be sensitive to the temperature for the phosphor Ba₄BiTb_0.999Eu_0.001O(BO₃)₄ upon 377 nm excitation. The above results demonstrate that Ba₄BiTb_1−xEu_xO(BO₃)₄ phosphors have potential as multifunctional materials for solid-state lighting and temperature sensing applications.