Two new rare-earth borates Sr 2 Tb 3 B 27- δ O 46 and Ba 2 Eu 3 B 27- δ O 46 ( δ = 2/3): syntheses, crystal structures, and luminescence properties.

Two new alkali-earth and rare-earth metal borates, Sr 2 Tb 3 B 27- δ O 46 and Ba 2 Eu 3 B 27- δ O 46 ( δ = 2/3), have been prepared by high-temperature solution reactions at 950 °C. The single-crystal XRD analysis showed that the borates crystallize in the rhombohedral space group R 3 with the cell parameters a = 7.7468(1) Å, c = 46.3657(5) Å, V = 2409.75(3) Å 3 , Z = 3 and a = 7.7964(1) Å, c = 46.5086(6) Å, V = 2448.23(7) Å 3 , Z = 3, respectively, which further confirms that "LnMB 9 O 16 " has the right formula of M 2 Ln 3 B 27- δ O 46 ( δ = 2/3). Their crystal structures consist of 3D networks constructed by Tb(Eu)O 6 trigonal prisms, BO 3 planar triangles, and BO 4 tetrahedra, with large cavities accommodating Sr 2+ (Ba 2+ ) cations. Furthermore, the phase composition, morphology, IR, Raman, and XPS spectra as well as photoluminescence properties of these two compounds were studied. Upon excitation by ultraviolet radiation, Sr 2 Tb 3 B 27- δ O 46 exhibits the characteristic emission lines originating from Tb 3+ corresponding to 5 D 4 - 7 F 6,5,4,3,2,1,0 transitions, whereas Ba 2 Eu 3 B 27- δ O 46 displays bright red emission from Eu 3+ with four groups of emission bands associated with 5 D 0 → 7 F 1,2,3,4 transitions. Both phosphors show stable luminescence and color purity at elevated temperatures. As it may be expected, Sr 2 Tb 3 B 27- δ O 46 and Ba 2 Eu 3 B 27- δ O 46 ( δ = 2/3) are promising green (Tb) and red (Eu) components for use in WLEDs.