Syntheses, crystal structure and luminescent properties of polyborates PbLnB₇O₁₃ (Ln = Gd, Sm) with a 2D [B₇O₁₃]_∞ framework

Two new polyborates, PbLnB₇O₁₃ (Ln = Gd, Sm), have been prepared and their structures were determined by single crystal X-ray diffraction analysis. The results show that they are isostructure, crystallize in a non-centrosymmetric space group P2₁ and feature a 2D layer structure that is composed of [B₇O₁₃]_∞ and [Ln]_∞ layers. The [B₇O₁₃]_∞ layer is constructed by BO₃ triangles and BO₄ tetrahedra with the fundamental building block of B₇O₁₇ (3∆4□: <∆2□>∆<∆2□>). Moreover, a series of Sm-doped solid solutions PbGd_1−xSm_xB₇O₁₃ (x=0.005–1) were synthesized and their photoluminescence properties were studied. Under near-UV light (403 nm) excitation, they exhibit intense orange emission centered at 602 nm, due to the ⁴G_5/2→⁶H_7/2 transition of Sm³⁺ activator. We may expect that PbGd_1−xSm_xB₇O₁₃ could be used as a good orange phosphor pumped by near UV light LED chips.