Synthesis and crystal structure of three silver indium double phosphates

NASICON-type Na3.6Lu1.8-x(PO4)3:xEu3+ phosphors: structure and luminescence

Na_3.6Lu_1.8-x(PO₄)₃:xEu³⁺ phosphors were synthesized by a high-temperature solid-state reaction. A powder X-ray diffraction study revealed that homogeneous solid solutions with a NASICON-type structure were formed at 0 ≤ x ≤ 0.7. The Na_3.6Lu_1.8(PO₄)₃ structure was refined from the powder X-ray diffraction data and the cation distribution in the lattice sites of the NASICON-type structure was revealed. The refinement indicates structural disorder caused by the displacement of a part of Lu cations along the c axis inside the (Lu/Na)O₆ octahedra that is confirmed by the broadened emission lines of Eu³⁺, which substitutes Lu cations. The highest Eu³⁺ luminescence intensity is found in Na_3.6Lu_1.8-x(PO₄)₃:xEu³⁺ for x = 0.5, whereas a further increase of the Eu³⁺ content leads to concentration quenching that is shown to occur due to the dipole-dipole interaction. An enhanced temperature stability of the Eu³⁺ emission was observed at the excitation energy of 3.23 eV. At this excitation energy, thermal quenching of the emission caused by the ⁷F₀ → ⁵L₇ transitions is compensated by the intensity increase of the emission related to the ⁷F₁ → ⁵G_J transitions, which occurs due to the increase of the ⁷F₁ level population, induced by a temperature rise.

Crystal structure of the alluaudite Ag2Mn3(VO4)3

The new compound Ag2Mn3(VO4)3 was synthesized by hydrothermal and solid state reaction routes, and its crystal structure was determined from single-crystal X-ray diffraction data. Ag2Mn3(VO4)3 crystallizes with a monoclinic symmetry, space group C2/c, with a=11.8968(11) Å, b=13.2057(13) Å, c=6.8132(7) Å, β=111.3166(15) (°) and V=997.16(17) Å3 (Z=4). Its crystal refinement yielded the residual factors R(F)=0.0249 and wR(F 2)=0.0704 for 95 parameters and 1029 independent reflections at a 3σ(I) level. Ag2Mn3(VO4)3 can be considered as a new member of the AA′MM′2(XO4)3 alluaudite family. The specific arrangement of M and M′ octahedral sites and of X tetrahedral sites gives rise to two different channels aligned along the crystallographic c-axis and containing the A and A′ sites. The A, A′, M, and X sites are fully occupied by Ag+, Mn2+, and V5+, respectively; whereas a Mn2+/Mn3+ mixture is observed in the M′ site.

Structural features of two novel alluaudite-like arsenates Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5

Two new compounds, Cd1.16Zn2.34(AsO4)1.5(HAsO4)(H2AsO4)0.5 (1) and Cd0.74Mg2.76(AsO4)1.5(HAsO4)(H2AsO4)0.5 (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O4(OH0.5)2, M1aO4(OH0.5)2, M2O5(OH0.5), and M2aO5(OH0.5) octahedra (M1, M1a = Zn, Cd; M2, M2a = Zn for 1, and M1, M1a = Mg, Cd; M2, M2a = Mg for 2) that are stacked parallel to (1 0 1) and are connected by the [(AsO4)0.5(AsO3(OH))0.5]2.5- and [(AsO4)0.5(AsO2(OH)2)0.5]2- tetrahedra. These chains produce two types of channels parallel to the c-axis. Cd atoms are located in channels 2, while in channels 1 are situated hydrogen atoms of OH groups. The infrared spectra clearly show the presence of broad O-H stretching and bending vibrations centred at 3236, 2392 1575 and 1396 cm-1 in (1), and 3210, 2379 1602 and 1310 cm-1 in (2). The O-H stretching frequency is in good agreement with O⋯O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed.