Original Oxo-Centered Frameworks in Bi3(VO4)O3 and Bi3.5(AsO4)(OH)0.5O3.5 by Supercritical Steam.

Two new bismuth compounds, oxovanadate Bi3(VO4)O3 and oxoarsenate Bi3.5(AsO4)(OH)0.5O3.5, were prepared using supercritical hydrothermal pressure. Dealing with the anionic sublattice, both crystal structures are built on anti-oxo-OBi4/OBi3 or -OBi4/OBi5 units connected together in infinite corrugated 2D layers surrounded by isolated XO4 (X = V or As) tetrahedra. These edifices complete a series initiated by the recent Bi3(PO4)O3 prepared under similar conditions. With the latter being assigned to the "simplest" bioxophosphate in terms of structural complexity, this aspect was investigated among the other compounds in their chemical ternaries. These phases are suggested to be high-pressure polymorphs, not possible to tackle when working at ambient pressure and temperature conditions.

Origin of Luminescence in La2MoO6 and La2Mo2O9 and Their Bi-Doped Variants.

In this article, lanthanum molybdenum oxides (La2MoO6 and La2Mo2O9) and their Bi-doped derivatives were investigated as potential rare-earth-free phosphors. An X-ray diffraction analysis coupled with an EDX study confirmed the purity of the samples and the insertion of bismuth in a 1 molar % amount. Kubelka-Munk-transformed reflectance spectra clearly indicated that the insertion of Bi induces a shortening of the optical gap in La2MoO6 but has no impact on that of La2Mo2O9. Moreover, excitation and emission spectra evidenced a strong temperature quenching effect in all materials. Also, the CIEx,y parameters at 77 K are almost identical with or without Bi doping for the two host lattices. Clearly, it was shown, by combining experimental data, ab initio calculations, and the empirical positioning of absorption bands that the luminescence of the Bi-doped La2MoO6 sample is mainly related to the host lattice itself and distortions induced by La/Bi substitution. The role of the Bi3+ dopant is indirect, and the luminescence is mainly due to a Mo-O charge transfer rather than an on-site Bi3+ 3P1,0 → 1S0 transition. Concerning La2Mo2O9, there is no effect following the insertion of Bi, implying that the role of Bi is insignificant.

Pb6O5(NO3)2: A Nonlinear Optical Oxynitrate Structurally Based on Lead Oxide Framework.

A high second harmonic generation response is demonstrated by a Pb6O5(NO3)2 lead oxynitrate whose identity was verified upon reinvestigation of the PbO-Pb(NO3)2 system. Its crystal structure exhibits a unique cationic [Pb6O5]2+ framework hosting orientationally ordered NO3- triangles in the channels. Easy preparation and high thermal stability (until ∼500 °C in air) suggest it to be a new promising NLO material.

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 ß = 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 ß-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 ß = 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.

Synthesis and modular structural architectures of mineralogically inspired novel complex Pb oxyhalides.

Three novel Pb oxyhalides, Pb3[O10Pb20](GeO4)4Cl10 (1), [O16Pb22][OPb](OH)I10(I,Br)(H2O) (2), and Pb5.5Si0.5O6Cl (3), have been prepared by high-temperature solid-state reactions (1 and 3) and hydrothermal method (2). The structure of 1 is based upon novel [O10Pb20](20+) layers of edge- and corner-sharing oxocentered OPb4 tetrahedra with cavities occupied by the GeO4 tetrahedral anions. The interlayer space contains low-occupied Pb sites and Cl(-) anions. The structure of 2 contains unique [O16Pb22][12+] layers of edge-sharing OPb4 tetrahedra with X(-) ions (X = I, Br) in and in between the layers. The structure of 3 is the first example of the Pb oxyhalide with the 3:1 ratio between the O-Pb and X sheets (X = halide). The unprecedented structure topologies and architectures observed in the title compounds are closely related to those observed in rare natural Pb oxyhalides that have no synthetic analogues to date.