Refinement of the crystal structures of praseodymium- and samariumoxoborate- bis(oxophosphate)-oxide, Ln7O6[BO3][PO4]2, (Ln = Pr, Sm)

Na3[Al2B6P4O22(OH)3](H2O)6 and Na3[Al2BP2O11](H2O)0.5: Two Remarkable Complex Aluminum Borophosphates

Two remarkable aluminum borophosphates (AlBPOs), namely, Na3[Al2B6P4O22(OH)3](H2O)6 (denoted as ABPO1) and Na3[Al2BP2O11](H2O)0.5 (denoted as ABPO2), have been designed and prepared by low-temperature flux syntheses. The exceptional open framework structure of ABPO1 is formed by a unique microanionic network [Al2B6P4O22(OH)3]n3-, which contains three types of 8-, 12-, and 16-membered ring (MR) tunnels. Interestingly, these tunnels are featured by a type of super-nanocage as large as ∼1.753 nm × 1.753 nm × 1.753 nm, which is the first example of AlBPOs containing extra-large cages. Importantly, it was found that Na+ can be partially exchanged by K+, Sr2+, Cd2+, and Ni2+, which means that it is a potential ionic exchanger for removing radionuclides and toxic cations. The structure of ABPO2 features a unique 2D anionic AlBPO layer composed of corner-sharing AlO6 octahedra and AlO4, BO4, and PO4 tetrahedra. To the best of our knowledge, this is the first example of both AlO6 octahedra and AlO4 tetrahedra being contained in the structure. 9-MRs can be observed along the b-axis. Herein, the syntheses and topological structures of ABPO1 and ABPO2 as well as elemental analysis, thermal stability, infrared spectroscopy, UV-vis diffuse reflectance, structural properties, and ionic exchange properties are also discussed.

Design, synthesis, crystal structure and luminescent properties introduced by Eu3+ of a new type of rare-earth borophosphate CsNa2REE2(BO3)(PO4)2 (REE = Y, Gd)

The rich compositional and structural diversity of borophosphates provides a wide variety of host lattices for luminescent materials. Herein, we report a borophosphate, CsNa₂REE₂(BO₃)(PO₄)₂ (REE = Y, Gd), with a new type of three-dimensional (3D) anionic framework of [REE₂(BO₃)(PO₄)₂]_∞. In this structure, REE³⁺ ions are in a linear array and the nearest intraline REE-REE distance is above 6.9 Å. Surprisingly, the Eu³⁺ activated phosphors CsNa₂REE_2(1-x)Eu_2x(BO₃)(PO₄)₂ show an insignificant concentration quenching effect; the higher the Eu³⁺ concentration, the larger the absolute luminescent external quantum yield. The 100% Eu³⁺ phosphor CsNa₂Eu₂(BO₃)(PO₄)₂ possesses an IQY of 59% under 394 nm excitation. Moreover, CsNa₂Eu₂(BO₃)(PO₄)₂ phosphor possesses superior thermal stability in the range 30-200 °C, retaining more than 96% of its initial intensity at 200 °C. We believe the prepared phosphor has potential application as a red phosphor for NUV excited LEDs.

Pure and RE3+-Doped La7O6(VO4)3 (RE = Eu, Sm): Polymorphism Stability and Luminescence Properties of a New Oxyvanadate Matrix

Two polytypes of the new oxyvanadate matrix La₇O₆(VO₄)₃ were identified and deeply characterized. The crystal structure of the α-polytype was solved using a combination of precession electron diffraction and powder X-ray diffraction (XRD) techniques. It crystallizes in a monoclinic unit cell with space group P2₁, a = 13.0148(3) Å, b = 19.1566(5) Å, c = 7.0764(17) Å, and β = 99.87(1)°. Its structure is built upon [La₇O₆]⁹⁺ polycationic units at the origin of a porous 3D network, evidencing rectangular channels filled by isolated VO₄ tetrahedra. An in situ high-temperature XRD study highlights a number of complex phase transitions assorted with the existence of a β-polytype also refined in a monoclinic unit cell, space group P2₁/n, a = 13.0713(4) Å, b = 18.1835(6) Å, c = 7.1382(2) Å, and β = 97.31(1)°. Thus, during the transitions, while the polycationic networks are almost identical, the vanadate's geometry is largely modified. The use of Eu³⁺ and Sm³⁺ at different concentrations in the host lattice is possible using solid-state techniques. The photoluminescence (PL), PL excitation (PLE) spectra, and luminescence decay times were recorded and discussed. The phosphors present an emission light, being bright and reddish orange after excitation under UV. This is mainly due to the V-O band and f-f transitions. Whatever the studied polytype, the final luminescence properties are retained during the heating/cooling process.