Three New Alkaline Beryllium Borates LiBeBO₃, Li₆Be₃B₄O₁₂, and Li₈Be₅B₆O₁₈ in the Ternary Phase Diagrams Li₂O–BeO–B₂O₃

The phase diagram in the Li₂O–BeO–B₂O₃ system has been systematically investigated by the methods of visual polythermal analysis, spontaneous crystallization, and X-ray diffraction. Three new alkaline beryllium borates, namely, LiBeBO₃, Li₆Be₃B₄O₁₂, and Li₈Be₅B₆O₁₈, were synthesized with molten fluxes based on Li₂O–B₂O₃ solvent in this system. All of the materials are centrosymmetric. The similarity of the fundamental building block of the title compounds has been compared. Thermal analysis and powder XRD studies were applied to determine phase relation and their incongruent melting behavior. The UV–vis diffuse reflectance spectroscopy demonstrated that the UV cutoff edges of the aforementioned materials are all below 200 nm

Y(IO₃)₃ as a Novel Photocatalyst: Synthesis, Characterization, and Highly Efficient Photocatalytic Activity

Nonbonding layer-structured Y­(IO₃)₃ was successfully prepared by a simple hydrothermal route and investigated as a novel photocatalyst for the first time. Its crystal structure was characterized by X-ray diffraction, high-resolution transmission electron microscopy, and scanning electron microscopy. The optical absorption edge and band gap of Y­(IO₃)₃ have been determined by UV–vis diffuse reflectance spectra. Theoretical calculations of the electronic structure of Y­(IO₃)₃ confirmed its direct optical transition property near the absorption edge region, and the orbital components of the conduction band and valence band (VB) were also analyzed. The photocatalytic performance of Y­(IO₃)₃ was evaluated by photooxidative decomposition of rhodamine B under ultraviolet light irradiation. It demonstrated that Y­(IO₃)₃ exhibits highly efficient photocatalytic activity, which is much better than those of commercial TiO₂ (P25) and important UV photocatalysts BiOCl and BiIO₄. The origin of the excellent photocatalytic performance of Y­(IO₃)₃ was investigated by electron spin resonance and terephthalic acid photoluminescence techniques. The results revealed that the highly strong photooxidation ability that resulted from its very positive VB position should be responsible for the excellent photocatalytic performance

Ce and F Comodification on the Crystal Structure and Enhanced Photocatalytic Activity of Bi₂WO₆ Photocatalyst under Visible Light Irradiation

The novel Ce and F codoped Bi₂WO₆ samples have been successfully obtained by a facile one-step hydrothermal reaction for the first time. They were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The presence of Ce³⁺, Ce⁴⁺, and F^– dopants in Bi₂WO₆ was confirmed by XPS. The change of microstructure and optical band gap has also been observed after the doping of Ce and F. Under visible light, the as-synthesized plate-like F–Ce–Bi₂WO₆ sample exhibits a much better visible-light-responsive photocatalytic performance than pure Bi₂WO₆ for the degradation of RhB and photocurrent (PC) generation. The mechanism of high photcatalytic activity was also suggested on the basis of the PL spectra, electrochemical impedance spectra (EIS), and active species trapping measurements. The results indicated that the synergistic effect of the Ce and F dopants is responsible for the efficient separation and migration of photoinduced charge carriers, thus resulting in the remarkably improved photocatalytic activity

Fabrication of Multiple Heterojunctions with Tunable Visible-Light-Active Photocatalytic Reactivity in BiOBr–BiOI Full-Range Composites Based on Microstructure Modulation and Band Structures

The fabrication of multiple heterojunctions with tunable photocatalytic reactivity in full-range BiOBr–BiOI composites based on microstructure modulation and band structures is demonstrated. The multiple heterojunctions are constructed by precipitation at room temperature and characterized systematically. Photocatalytic experiments indicate that there are two types of heterostructures with distinct photocatalytic mechanisms, both of which can greatly enhance the visible-light photocatalytic performance for the decomposition of organic pollutants and generation of photocurrent. The large separation and inhibited recombination of electron–hole pairs rendered by the heterostructures are confirmed by electrochemical impedance spectra (EIS) and photoluminescence (PL). Reactive species trapping, nitroblue tetrazolium (NBT, detection agent of ^•O₂^–) transformation, and terephthalic acid photoluminescence (TA-PL) experiments verify the charge-transfer mechanism derived from the two types of heterostructures, as well as different enhancements of the photocatalytic activity. This article provides insights into heterostructure photocatalysis and describes a novel way to design and fabricate high-performance semiconductor composites

A Deep-Ultraviolet Nonlinear Optical Crystal: Strontium Beryllium Borate Fluoride with Planar Be(O/F)₃ Groups

A new strontium beryllium borate fluoride, Sr₃[(Be_<i>x</i>B_1–<i>x</i>)₃B₃O₁₀]­[Be­(O_1–<i>x</i>F_<i>x</i>)₃] <i>x</i> = 0.30 (SBBOF), designed to be used in the deep-UV nonlinear optical (NLO) application, was grown by the spontaneous crystallization of a molten flux of SrO–B₂O₃–LiF. It crystallizes in the space group <i>R3m</i> (No. 160) with the following unit cell dimensions: <i>a</i> = 10.3179(11) Å, <i>c</i> = 8.3958(13) Å, <i>V</i> = 774.1(2) ų, and <i>Z</i> = 3. SBBOF consists of [(Be_<i>x</i>B_1–<i>x</i>)₃B₃O₁₀] anionic groups and isolated [Be­(O_1–<i>x</i>F_<i>x</i>)₃] planar groups. Importantly, a new strategy to improve the birefringence was introduced by changing the local configuration of isolated structural units from trigonal pyramids to planar triangles. UV–vis diffuse reflectance spectroscopy indicates that the short-wavelength absorption edge of SBBOF is below 200 nm. The band structure and refractive index were calculated. Second harmonic generation (SHG) was measured using the Kurtz and Perry technique, which showed that SBBOF is a phase-matchable material in both visible and UV regions, and its measured SHG coefficient is 2.2 times as large as that of <i>d</i>₃₆ (KDP) at 1064 nm

A Deep-Ultraviolet Nonlinear Optical Crystal: Strontium Beryllium Borate Fluoride with Planar Be(O/F)₃ Groups

A new strontium beryllium borate fluoride, Sr₃[(Be_<i>x</i>B_1–<i>x</i>)₃B₃O₁₀]­[Be­(O_1–<i>x</i>F_<i>x</i>)₃] <i>x</i> = 0.30 (SBBOF), designed to be used in the deep-UV nonlinear optical (NLO) application, was grown by the spontaneous crystallization of a molten flux of SrO–B₂O₃–LiF. It crystallizes in the space group <i>R3m</i> (No. 160) with the following unit cell dimensions: <i>a</i> = 10.3179(11) Å, <i>c</i> = 8.3958(13) Å, <i>V</i> = 774.1(2) ų, and <i>Z</i> = 3. SBBOF consists of [(Be_<i>x</i>B_1–<i>x</i>)₃B₃O₁₀] anionic groups and isolated [Be­(O_1–<i>x</i>F_<i>x</i>)₃] planar groups. Importantly, a new strategy to improve the birefringence was introduced by changing the local configuration of isolated structural units from trigonal pyramids to planar triangles. UV–vis diffuse reflectance spectroscopy indicates that the short-wavelength absorption edge of SBBOF is below 200 nm. The band structure and refractive index were calculated. Second harmonic generation (SHG) was measured using the Kurtz and Perry technique, which showed that SBBOF is a phase-matchable material in both visible and UV regions, and its measured SHG coefficient is 2.2 times as large as that of <i>d</i>₃₆ (KDP) at 1064 nm

Efficient Hg Vapor Capture with Polysulfide Intercalated Layered Double Hydroxides

We report detailed studies showing that the novel layered polysulfide compounds S_<i>x</i>-LDH (S_<i>x</i>^2–, polysulfides, <i>x</i> = 2, 4, 5; LDH, Mg–Al layered double hydroxides) can capture efficiently large quantities of mercury (Hg⁰) vapor. During the adsorption process, the interlayer polysulfides [S_<i>x</i>]^2– react with Hg⁰ through their S–S bond to produce HgS. The structure of S_<i>x</i>-LDH before and after Hg-adsorption was characterized with X-ray diffraction, vibration spectroscopy, and scanning electron microscopy. The presence of adsorbed Hg was verified by weight gain, inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy. Despite their relatively low surface areas, the S₂-LDH, S₄-LDH, and S₅-LDH samples show excellent Hg capture capacities of 4.9 × 10⁵, 7.4 × 10⁵, and 1.0 × 10⁶ μg/g, respectively, corresponding to 50–100% adsorption rates by weight, highlighting the potential of these materials in natural gas purification. The Hg-capture efficiency and mechanism in S_<i>x</i>-LDH are supported by control experiments with K₂S₄, S₈, LDH-NO₃-CoS₄, and MgAl-NO₃-LDH

Crystal Growth of Tl₄CdI₆: A Wide Band Gap Semiconductor for Hard Radiation Detection

We report the synthesis, physical characterization, and crystal growth of Tl₄CdI₆. We show that this material has good photoconductivity and is a promising semiconductor for room temperature X-ray and γ-ray detection. Large single crystals were grown by the vertical Bridgman method and cut to dimensions appropriate for detector testing. Single crystal X-ray diffraction refinements confirm that Tl₄CdI₆ crystallizes in the tetragonal crystal system with a centrosymmetric space group of <i>P</i>4<i>/mnc</i>, with a calculated density of 6.87 g/cm³. Thermal analysis and high-temperature synchrotron powder diffraction studies were used to determine phase relationships and crystallization behavior during crystal growth. We have elucidated the reason for different colors encountered when synthesizing or growing single crystals of Tl₄CdI₆ (yellow, red, and black), and it is the presence of a small amount of TlI impurity. We report proper crystal growth conditions to obtain essentially pure yellow Tl₄CdI₆ crystals. The material having the yellow color has a band gap of 2.8 eV. First-principles density functional theory calculations indicate a direct band gap at the Γ point of the Brillouin zone. The Tl₄CdI₆ crystals have a resistivity of 10¹⁰ Ω·cm. Photoconductivity measurements on the as-grown crystals show mobility-lifetime product on the order of 10^–4 cm²/V for both electrons and holes. The promising detector properties of this material are confirmed by preliminary measurements showing a clear spectral response to an Ag X-ray source, which classifies Tl₄CdI₆ as an emerging material for radiation detection

Cs₂Hg₃S₄: A Low-Dimensional Direct Bandgap Semiconductor

Cs₂Hg₃S₄ was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs₂S₄. Cs₂Hg₃S₄ crystallizes in the <i>Ibam</i> spacegroup with <i>a</i> = 6.278(1) Å, <i>b</i> = 11.601(2) Å, and <i>c</i> = 14.431(3)­Å; <i>d</i>_calc = 6.29 g/cm³. Its crystal structure consists of straight chains of [Hg₃S₄]_<i>n</i>^2<i>n</i>– that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs⁺ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the <i>a</i>, <i>b</i>, and <i>c</i> axes were assessed at 1.56 × 10^–5, 2.79 × 10^–5, and 3.04 × 10^–5 K^–1, respectively. Large single-crystals up to ∼5 cm in length and ∼1 cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs₂Hg₃S₄ gave resistivity ρ of ≥10⁸ Ω·cm and carrier mobility-lifetime (μτ) products of 4.2 × 10^–4 and 5.82 × 10^–5 cm² V^–1 for electrons and holes, respectively. Cs₂Hg₃S₄ is a semiconductor with a bandgap <i>E</i>_g ∼ 2.8 eV and exhibits photoluminescence (PL) at low temperature. Electronic band structure calculations within the density functional theory (DFT) framework employing the nonlocal hybrid functional within Heyd–Scuseria–Ernzerhof (HSE) formalism indicate a direct bandgap of 2.81 eV at Γ. The theoretical calculations show that the conduction band minimum has a highly dispersive and relatively isotropic mercury-based s-orbital-like character while the valence band maximum features a much less dispersive and more anisotropic sulfur orbital-based band