Structure Determination and Luminescent Property Studies of the Single Crystal Na3Sm(BO3)2

Crystallization of A3Ln(BO3)2 (A = Na, K; Ln = Lanthanide) from a Boric Acid Containing Hydroxide Melt: Synthesis and Investigation of Lanthanide Borates as Potential Nuclear Waste Forms

A series of alkali metal rare-earth borates were prepared via high-temperature flux crystal growth, and their structures were characterized by single crystal X-ray diffraction (SXRD). Na₃Ln(BO₃)₂ (Ln = La-Lu) crystallize in the monoclinic space group P2₁/n, the potassium series K₃Ln(BO₃)₂ (Ln = La-Tb) crystallize in the orthorhombic space group Pnma, while the Ln = Dy, Ho, Tm, Yb analogues crystallize in the orthorhombic space group Pnnm. To demonstrate the generality of this synthetic technique, high-entropy oxide (HEO) compositions K₃Nd_0.15(1)Eu_0.20(1)Gd_0.20(1)Dy_0.22(1)Ho_0.23(1)(BO₃)₂ and K₃Nd_0.26(1)Eu_0.29(1)Ho_0.22(1)Tm_0.14(1)Yb_0.10(1)(BO₃)₂ were obtained in single crystal form. Radiation damage investigations determined that these borates have a high radiation damage tolerance. To assess whether trivalent actinide analogues of Na₃Ln(BO₃)₂ and K₃Ln(BO₃)₂ would be stable, density functional theory was used to calculate their enthalpies of formation, which are favorable.

Na3Sm(PO4)2: (3+1)-dimensional commensurately modulated structure model and photoluminescence properties

For the first time, we determined the detailed crystal structure of Na3Sm(PO4)2 using single crystal X-ray diffraction and established the commensurately modulated structure model using the superspace formalism. The structure adopts a (3+1)-dimensional superspace group Pca21(0β0)000 with the modulation vector q=1/3b*. At the same time, the photoluminescent properties of Na3Sm(PO4)2 sintered at different temperatures between 800 and 1200°C were studied. Under near-UV excitation (402 nm), Na3Sm(PO4)2 shows intense characteristic emission bands of Sm3+ (561, 596, 642 nm) with the CIE coordinate of (0.5709, 0.4282), corresponding to orange color. The excitation spectrum covers a wide range from 350 nm to 470 nm, which indicates that Na3Sm(PO4)2 can be efficiently activated by near-UV or visuable LED ship.