Fuhui Liao

New high Tc multiferroics KBiFe2O5 with narrow band gap and promising photovoltaic effect

Intrinsic polarization of ferroelectrics (FE) helps separate photon-generated charge carriers thus enhances photovoltaic effects. However, traditional FE with transition-metal cations (M) of d0 electron in MO6 network typically has a band gap (Eg) exceeding 3.0 eV. Although a smaller Eg (2.6 eV) can be obtained in multiferroic BiFeO3, the value is still too high for optimal solar energy applications. Computational “materials genome” searches have predicted several exotic MO6 FE with Eg < 2.0 eV, all thus far unconfirmed because of synthesis difficulties. Here we report a new FE compound with MO4 tetrahedral network, KBiFe2O5, which features narrow Eg (1.6 eV), high Curie temperature (Tc ~ 780 K) and robust magnetic and photoelectric activities. The high photovoltage (8.8 V) and photocurrent density (15 μA/cm2) were obtained, which is comparable to the reported BiFeO3. This finding may open a new avenue to discovering and designing optimal FE compounds for solar energy applications.

Novel phosphors of Eu3+, Tb3+ or Bi3+ activated Gd2GeO5

Abstract Novel phosphors of Eu 3+ , Tb 3+ or Bi3+ doped Gd2GeO5 were synthesized and their photoluminescent and cathodoluminescent properties were investigated. (Gd1−xEux)2GeO5 and (Gd1−xTbx)2GeO5 formed continuous solid solution in the range of x=0.0–1.0. Gd2GeO5:Eu3+ and Gd2GeO5:Bi3+ presented bright red and blue luminescence for both UV and cathode ray excitation, respectively. While Gd2GeO5:Tb3+ gave bright green cathodoluminescence. In all three phosphors, the energy transfer from Gd3+ to activators (e.g. Eu 3+ , Tb 3+ or Bi3+) occurred.

Preparation and X-ray characterization of low-temperature phases of R2SiO5 (R = rare earth elements)

Low-temperature phases of R2SiO5 (R 5 Y, Tb, Dy, Ho, Er, Tm, and Yb) were synthesized by the sol-gel method. The X-ray powder diffraction patterns for these new phases were indexed with the monoclinic unit cell, and the unit cell parameters were refined. The structure of Y2SiO5 with the space group P21/c was determined by powder diffraction data.

Microporous Aluminoborates with Large Channels: Structural and Catalytic Properties

Channel zapping: PKU-1 and newly synthesized PKU-2 (Al(2)B(5)O(9)(OH)(3)⋅n H(2)O; see picture) possess microporous structures with 18-ring and 24-ring channels, respectively. They show high reactivity and size selectivity in the cyanosilylation of aldehydes as heterogeneous Lewis acid catalysts. The different channel sizes determine the substrate selectivity. These examples demonstrate the potential of octahedron-based aluminoborate channels in catalysis.

Synthesis and structure of an aluminum borate chloride consisting of 12-membered borate rings and aluminate clusters.

A new aluminum borate chloride (PKU-8) was synthesized in a flux of boric acid, and the structure was established using powder X-ray diffraction techniques. PKU-8 contains an unusual framework structure of a large cage consisting of 12-membered borate rings [B 12O 30] and aluminate octahedra clusters [Al 7O 24].

Syntheses and crystal structures of two new bismuth hydroxyl borates containing [Bi2O2]2+ layers: Bi2O2[B3O5(OH)] and Bi2O2[BO2(OH)].

Two new bismuth hydroxyl borates, Bi(2)O(2)[B(3)O(5)(OH)] (I) and Bi(2)O(2)[BO(2)(OH)] (II), have been synthesized under hydrothermal conditions. Their structures were determined by single-crystal and powder X-ray diffraction data, respectively. Compound I crystallizes in the orthorhombic space group Pbca with the lattice constants of a = 6.0268(3) Å, b = 11.3635(6) Å, and c = 19.348(1) Å. Compound II crystallizes in the monoclinic space group Cm with the lattice constants of a = 5.4676(6) Å, b = 14.6643(5) Å, c = 3.9058(1) Å, and β = 135.587(6)°. The borate fundamental building block (FBB) in I is a three-ring unit [B(3)O(6)(OH)](4-), which connects one by one via sharing corners, forming an infinite zigzag chain along the a direction. The borate chains are further linked by hydrogen bonds, showing as a borate layer within the ab plane. The FBB in II is an isolated [BO(2)(OH)](2-) triangle, which links to two neighboring FBBs by strong hydrogen bonds, resulting in a borate chain along the a direction. Both compounds contain [Bi(2)O(2)](2+) layers, and the [Bi(2)O(2)](2+) layers combine with the corresponding borate layers alternatively, forming the whole structures. These two new bismuth borates are the first ones containing [Bi(2)O(2)](2+) layers in borates. The appearance of Bi(2)O(2)[BO(2)(OH)] (II) completes the series of compounds Bi(2)O(2)[BO(2)(OH)], Bi(2)O(2)CO(3), and Bi(2)O(2)[NO(3)(OH)] and the formation of Bi(2)O(2)[B(3)O(5)(OH)] provides another example in demonstrating the polymerization tendency of borate groups.

Ultrasensitive sorption behavior of isostructural lanthanide–organic frameworks induced by lanthanide contraction

Reactions of lanthanide nitrate and the trigonal-planar ligand 1,3,5-benzenetrisbenzoic acid (H3BTB) gave rise to a family of lanthanide–organic frameworks (LOFs) formulated as Ln(BTB)(H2O), where Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Yb. Single-crystal X-ray diffraction (XRD) analysis of Pr-LOF reveals a three-dimensional network with an ultramicroporous structure. Powder XRD and thermogravimetric analyses show that these LOFs are isostructural and can firmly stabilize up to 550 °C. Influenced by the opposite effects of ionic radius and molecular weight from La(III)–Yb(III), the related LOFs with the highest uptake of CO2 and CH4 happen to be Nd-LOF and Sm-LOF, respectively. Moreover, the isotherms of N2 at 77 K and benzene vapor at 298 K further evidence that lanthanide contraction greatly affects the adsorption performance of the resulting materials, bringing about stepwise and hysteretic sorption behavior for La-LOF to Pr-LOF but type I isotherms for the rest of the LOFs. This work represents the first systematic study of a family of lanthanide-based metal–organic frameworks with ultrasensitive sorption behavior induced by the lanthanide contraction.

Influence of Rare Earth Sc and La to the Luminescent Properties of FED Blue Phosphor Y 2SiO5 : Ce

Luminescent properties of Sc 3+ and La 3+ doped (Y 0.995 Ce 0.005 ) 2 SiO s phosphors were studied. In the Sc 3+ doped system (Y 0.995-x Sc x Ce 0.005 ) 2 SiO 5 , the solid solution extends to x = 0.65, but in the La 3+ doped system (Y 0.995-x, La x Ce 0.005 ) 2 SiO 5 , the solid solution range is not over the La 3+ content of x = 0.05. For La 3+ doped samples, the photoluminescence (PL) increases about 30% and cathodoluminescence (CL) increases about 10%. Additionally the color saturation is also improved with La 3+ doping. The mechanisms for these improvements are discussed. For the Sc 3+ doped samples, both PL and CL, clearly decrease. These phosphors may be useful in field emission displays TEED).

Influence of Rare Earth Elements (Sc, La, Gd, and Lu) to the Luminescent Properties of FED Blue Phosphor Y 2SiO5 : Ce

The emission spectra of Y 2 SiO 5 :Ce were analyzed by Gaussian peak fitting. The emission mainly can be attributed to the transitions of 5d to 2 F 5/2 and 2 F 7/2 of Ce 3+ ions. A weak peak at ∼460 nm arises from an independent luminescent center. Both the luminescent intensity and the peak height ratio are affected by Ce 3+ content. For choosing an optimized Ce 3+ content, the balance between brightness and color saturation was considered. Sc 3+ and La 3+ cannot replay Y 3+ to form solid solutions and doping them reduced luminescence very much. Y 3+ can be replaced by Gd 3+ and Lu 3+ to form solid solution in some ranges. The replacement of Gd 3+ decreased the luminescence, whereas Lu 3+ enhances the luminescence about 20% under cathode ray excitation. Ludoping also improves color saturation.

Na8[Cr4B12P8O44(OH)4][P2O7].nH2O: a 3D borophosphate framework with spherical cages.

A chromium borophosphate-phosphate (Na(8)[Cr(4)B(12)P(8)O(44)(OH)(4)][P(2)O(7)]nH(2)O, 1), which has an unusual 3D framework structure, was synthesized under hydrothermal conditions. The framework consists of spherical cages composed of CrO(6), PO(4), BO(4), and BO(3) polyhedra. The cages are located at the vertices and the body center of the cubic cell and are interconnected through 12-membered-ring windows along the {111} direction. The actual framework structure is very complex, but the description can be simplified by using the 5-connected fundamental building cluster [CrP(5)B(3)O(24)](11-). In addition, 1 represents the first borate-rich borophosphate that contains a 3D borophosphate partial framework (3(over)infinity[B(3)P(2)O(11)(OH)]) in which the fundamental building unit is an oB dreier single ring (Delta4 square:square square). The cavities of the framework are filled with disengaged water molecules and Na(+) counterions. The former can be reversibly desorbed and reabsorbed and the latter can be exchanged by Li(+) ions, which results in significant shrinkages of the cell volume.