A novel mixed metal orthoborate Ba2ZnTb2(BO3)4: Crystal structure and multicolor emitting properties introduced by Eu3+ doping

Abstract

Novel mixed metal orthoborate Ba2ZnTb2(BO3)4 was obtained through the high-temperature solid-state reaction at 950 °C. Its crystal structure was determined by single-crystal X-ray diffraction for the first time. The compound crystallizes in the orthorhombic system, Pbca space group, with cell parameters a = 13.4360(1), b = 6.4539(1), c = 25.3262(2) Å, V = 2196.15(4) Å3 and Z = 8. It represents a novel structure type in which ZnO4 tetrahedra and TbO8 polyhedra are interconnected via corner-, edge-, and face-sharing to form 1D [Zn2Tb4O24]n32n− chains. Some B atoms reside in triangular voids of the chains to strengthen the structure, while the others ‘stitch’ the chains together via B–O bonds to create a 3D [Zn2Tb4(BO3)8]n8n− network, with the open channels hosting Ba2+ ions. In addition, polycrystalline samples of Ba2ZnTb2-2xEu2x(BO3)4 (0 ≤ x ≤ 1) were synthesized via solid-state reaction at 780 °C and systematically characterized by powder XRD combined with Rietveld refinements, SEM, IR/Raman, XPS and photoluminescence spectroscopy. As it was revealed, due to the Tb3+ → Eu3+ energy transfer, the emission color of the obtained phosphors can be continuously tuned from green (0.2947, 0.5876) to orange (0.5766, 0.3994) and eventually to red (0.6419, 0.3536) upon the near-UV excitation at 377 nm through changing the Eu3+/Tb3+ ratio. The representative Ba2ZnTb1.998Eu0.002(BO3)4 sample shows a QY of ∼14.84 % (λex = 377 nm), and its emission intensity at 423 K still maintains ∼66 % of that at 303 K. All these observations indicate that, by properly doping activators and selecting the excitation wavelength, this borate phosphor displays multicolor tunable emission that may have potential applications in multicolor lighting and color display.