Novel tantalum phosphate Na13Sr2Ta2(PO4)9: synthesis, crystal structure, DFT calculations and Dy3+-activated fluorescence performance

Rb9-xAg3+xSc2(WO4)9: a new glaserite-related structure type, rubidium disorder, ionic conductivity

A new triple tungstate Rb_9-xAg_3+xSc₂(WO₄)₉ (0 ≤ x ≤ 0.15) synthesized by solid state reactions and spontaneous crystallization from melts presents a new structure type related to those of Cs₇Na₅Yb₂(MoO₄)₉ and Na₁₃Sr₂Ta₂(PO₄)₉. The title compound in centrosymmetric space group Cmcm contains dimers of two ScO₆ octahedra sharing corners with three bridging WO₄ tetrahedra. Three pairs of opposite terminal WO₄ tetrahedra are additionally linked by AgO₂ dumbbells to form {Ag₃[Sc₂(WO₄)₉]}^9- groups, which together with some rubidium ions are packed in pseudohexagonal glaserite-like layers parallel to (001), but stacking of the layers is different in these three structures. In the title structure, the layers stack with a shift along the b axis and their interlayer space contains disordered Rb⁺ cations partially substituted by Ag⁺ ions. Almost linear chains of incompletely filled close Rb3a-Rb3d positions (the shortest distances Rb-Rb are 0.46 to 0.64 Å) are found to locate approximately along the b axis. This positional disorder and the presence of wide common quadrangular faces of Rb2 and Rb3a-Rb3d coordination polyhedra favor two-dimensional ionic conductivity in the (001) plane with Rb⁺ and Ag⁺ carriers, which was confirmed with bond valence sum (BVS) maps. Electrical conductivity measurements on Rb₉Ag₃Sc₂(WO₄)₉ ceramics revealed a first-order superionic phase transition at 570 K with a sharp increase in the electrical conductivity. The conductivity σ_i = 1.8 × 10^-3 S cm^-1 at 690 K is comparable with the value of 1.0 × 10^-3 S cm^-1 (500 K) observed earlier for rubidium-ion transport in pyrochlore-like ferroelectric RbNbWO₆.

Recent trends in crystallography - a current IUCr journals perspective

This Editorial considers the impact of recent work published in IUCrJ and other IUCr journals, as well as the relationship between IUCrJ and the other journals, in terms of where the most cited recent papers are used.

A novel stibium phosphate, LiBa(SbO)2(PO4)3: synthesis, crystal structure and RE3+-activated (RE = Tb3+ and Eu3+) fluorescence performance

A new stibium phosphate, lithium barium bis(antimony oxide) tris(phosphate), LiBa(SbO)₂(PO₄)₃, was prepared by the molten salt method with LiF as the flux. The crystal structure consists of an original three-dimensional anionic framework of [(SbO)₂(PO₄)₃]_∞ built from PO₄ tetrahedra sharing their corners with SbO₆ octahedra. This framework delimits one-dimensional tunnels where the lithium(I) and barium(II) ions are located. The UV-Vis spectrum shows that LiBa(SbO)₂(PO₄)₃ was transparent from 350 to 800 nm, and is thus suitable as a luminescent host matrix. We then used Tb³⁺ and Eu³⁺ activators to test its luminous performance and the purities of the prepared phosphors were studied by powder X-ray diffraction analysis with Rietveld refinements. Photoluminescence (PL) studies reveal that the emission spectra of 1 mol% RE³⁺-doped (RE = Tb and Eu) samples can be excited by 371 and 394 nm light, emitting green and orange-red light, respectively, for Tb³⁺ and Eu³⁺. The CIE coordinates were measured to be (0.295, 0.571) and (0.6027, 0.3967), and the luminescent lifetimes were calculated as 0.178 and 1.159 ms, respectively.

K3Eu5(PO4)6: hydrothermal synthesis, crystal structure and photoluminescence properties

An anhydrous orthophosphate, K₃Eu₅(PO₄)₆ (tripotassium pentaeuropium hexaphosphate), has been prepared by a high-temperature solid-state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single-crystal X-ray diffraction analysis (SC-XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three-dimensional framework of [Eu₅(PO₄)₆]_∞, with the tunnel filled by K⁺ ions. The IR spectrum, UV-Vis spectrum and luminescence properties of polycrystalline samples of K₃Eu₅(PO₄)₆, annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu³⁺ concentration (9.96 × 10²¹ ions cm^-3), the self-activated phosphor K₃Eu₅(PO₄)₆ shows s strong luminescence emission intensity with a quantum yield of 37%. Under near-UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu³⁺ ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.

A new disordered langbeinite-type compound, K2Tb1.5Ta0.5P3O12, and Eu3+-doped multicolour light-emitting properties

For the first time, a new langbeinite-type phosphate, namely potassium terbium tantalum tris(phosphate), K₂Tb_1.5Ta_0.5(PO₄)₃, has been prepared successfully using a high-temperature flux method and has been structurally characterized by single-crystal X-ray diffraction. The results show that its structure can be described as a three-dimensional open framework of [Tb_1.5Ta_0.5(PO₄)₃]_∞ interconnected by K⁺ ions. The Tb^III and Ta^V cations in the structure are disordered and occupy the same crystallographic sites. The IR spectrum, the UV-Vis spectrum, the morphology and the Eu³⁺-activated photoluminescence spectroscopic properties were studied. A series of Eu³⁺-doped phosphors, i.e. K₂Tb_1.5-xTa_0.5(PO₄)₃:xEu³⁺ (x = 0.01, 0.03, 0.05, 0.07, 0.10), were prepared via a solid-state reaction and the photoluminescence properties were studied. The results show that under near-UV excitation, the luminescence colour can be tuned from green through yellow to red by simply adjusting the Eu³⁺ concentration from 0 to 0.1, because of the efficient Tb³⁺→Eu³⁺ energy-transfer mechanism.