Polymorphism of Niobium Phosphate Bronze Na4Nb8P4O32 Deduced by the Packings of Structural Units: A Centrosymmetric Phase.

Herein, a new centrosymmetric phase Na4Nb8P4O32 (referred to as CS-Na4Nb8P4O32) was obtained by a molten salt method, which is a polymorph of niobium phosphate bronze Na4Nb8P4O32. CS-Na4Nb8P4O32 displays high structural similarity to the noncentrosymmetric Na4Nb8P4O32 phase (referred to as NCS-Na4Nb8P4O32): Distorted NbO6 octahedra are corner-coordinated to form ReO3-type layers, which are further joined together by isolated PO4 tetrahedra. However, two polymorphous phases adopt different packings of structural units, resulting in distinct symmetries. NbO3 layers and PO4 tetrahedra are reversely arranged along the crystallographic a direction in CS-Na4Nb8P4O32, thereby producing a centrosymmetric structure. The reverse packing cancels out all contributions of dipole moments originating from the distorted NbO6 octahedra; NCS-Na4Nb8P4O32 exhibits the C2-rotation distribution of NbO3 layers and PO4 tetrahedra, thus generating a noncentrosymmetric and polar structure. The C2-rotation packing of structural units brings a constructive addition of the dipole moments, further obtaining large calculated independent second harmonic generation susceptibilities. The study of structural evolution deduced by the packings of structural units in polymorphous Na4Nb8P4O32 might provide valuable insights into polymorphism and structural regulation.

Antimony Doping Enabled Photoluminescence Quantum Yield Enhancement in 0D Inorganic Bismuth Halide Crystals.

Owing to the exterior self-trapped excitons (STEs) with adjustable fluorescence beams, low-dimensional ns2-metal halides have recently received considerable attention in solid-state light-emitting applications. However, the photoluminescence (PL) mechanism in metal halides remains a major challenge in achieving high efficiency and controllable PL properties because the excited-state energy of ns2 conformational ions varies inhomogeneously with their coordination environments. Here, a novel zero-dimensional (0D) lead-free bismuth-based Rb3BiCl6·0.5H2O crystal was reported as a pristine crystal to modulate the optical properties. By doping Sb3+ ions with 5s2 electrons into Rb3BiCl6·0.5H2O crystals, bright orange emission at room temperature was obtained with a photoluminescence quantum yield of 39.7%. Optical characterizations and theoretical studies show that the Sb3+ doping can suppress the strong exciton-phonon coupling, optimize the electronic energy band structure, improve the thermal activation energy, soften the structural lattice of the host crystals, deepen the STE states, and ultimately lead to strong photoluminescence. This work manifests a fruitful manipulation in ripening bismuth-based halides with high-efficiency PL properties, and the PL enhancement mechanisms will guide future research in the exploration of emerging luminescent materials.

Co-substitution design: a new glaserite-type rare-earth phosphate K2RbSc(PO4)2 with high structural tolerance.

An alkali rare-earth phosphate K2RbSc(PO4)2 was successfully obtained as a derivative of glaserite-type K3Na(SO4)2 by co-substitution of K(1)O12 → RbO12, K(2)O10 → KO7, NaO6 → ScO6 and SO4 → PO4, while maintaining the original anionic framework. K2RbSc(PO4)2 exhibits a layered [Sc(PO4)2]∞ framework built from ScO6 octahedra and PO4 tetrahedra, with K and Rb residing in the interlayers. Its isostructural lanthanide analogues K2RbEr(PO4)2 and K2RbLu(PO4)2, inspired by an elemental substitution strategy, were also prepared by a high-temperature solid state reaction. The successful substitution indicates that the skeleton of K2RbSc(PO4)2 is stable with high structural tolerance, which can provide a possibility for substitution of resident ions to obtain diverse structural types and applications.

Atomic Substitution to Tune ScO6 Distortion in Ba2MSc2(BO3)4 (M = Na, K, Ba) to Acquire a Large Birefringence.

Replacing alkali metals (K, Na atoms) by an alkaline-earth metal (Ba atom), α-Ba3Sc2(BO3)4 (high-temperature phase) is successfully obtained by a molten salt method, taking Ba2K1.6Na0.4Sc2(BO3)4 as the parent template. Although both of them exhibit similar layered structures composed of ScO6 and BO3 units, α-Ba3Sc2(BO3)4 shows largely distorted ScO6 octahedra (Δd = 0.56) forced by the uniform tension of a larger space effect from BaO12 polyhedrons, rather than regular ScO6 octahedra like in Ba2K1.6Na0.4Sc2(BO3)4. Experimental measurements and calculated analyses elucidate that distorted ScO6 octahedra in α-Ba3Sc2(BO3)4, displaying a second-order Jahn-Teller (SOJT) effect, enlarge the experimental birefringence up to 0.14@550 nm, while Ba2K1.6Na0.4Sc2(BO3)4 with regular ScO6 octahedra only shows Δn = 0.11 under the same condition. In addition, other optical and thermal properties of the two title compounds were characterized. The experimental results indicate that Ba2K1.6Na0.4Sc2(BO3)4 and α-Ba3Sc2(BO3)4 are promising birefringent materials.

Ba1.09Pb0.91Be2(BO3)2F2: The First Pb-Containing Beryllium Borate Fluoride with Trigonal Prismatic PbO6 and 2D [Be3B3O6F3]∞ Layers.

Ba1.09Pb0.91Be2(BO3)2F2 (BPBBF), a previously unreported lead-containing beryllium borate fluoride, has been successfully grown through a high-temperature flux method. Its structure is solved by single-crystal X-ray diffraction (SC-XRD), and it is optically characterized via infrared, Raman, UV-vis-IR transmission, and polarizing spectra as well. SC-XRD data suggests that it can be indexed by a trigonal unit cell (space group P3m1) with lattice parameters a = 4.7478(6) Å, c = 8.3856(12) Å, Z = 1, and V = 163.70(5) Å. This material could be considered as a derivative of the Sr2Be2B2O7 (SBBO) structural motif. It consists of 2D [Be3B3O6F3]∞ layers in the crystallographic ab plane, with divalent Ba2+ or Pb2+ cations serving as spacers among the adjacent layers. Ba and Pb were found to adopt a disordered arrangement in the trigonal prismatic coordination within the BPBBF structural lattice, which is evidenced by both structural refinements against SC-XRD data and energy dispersive spectroscopy. The UV absorption edge (279.1 nm) and birefringence (Δn = 0.054@ 546.1 nm) of BPBBF are confirmed by UV-vis-IR transmission and polarizing spectra, respectively. The discovery of this previous unreported SBBO-type material, BPBBF, along with other reported analogues such as BaMBe2(BO3)2F2 (M = Ca, Mg, and Cd), provide a prodigious example for tuning the bandgap, birefringence, and short UV absorption edge via simple chemical substitution.

Efficient Synthesis and In Vitro Hypoglycemic Activity of Rare Apigenin Glycosylation Derivatives.

Apigenin is a natural flavonoid with significant biological activity, but poor solubility in water and low bioavailability limits its use in the food and pharmaceutical industries. In this paper, apigenin-7-O-ß-(6″-O)-d-glucoside (AG) and apigenin-7-O-ß-(6″-O-succinyl)-d-glucoside (SAG), rare apigenin glycosyl and succinyl derivatives formed by the organic solvent-tolerant bacteria Bacillus licheniformis WNJ02 were used in a 10.0% DMSO (v/v) system. The water solubility of SAG was 174 times that of apigenin, which solved the application problem. In the biotransformation reaction, the conversion rate of apigenin (1.0 g/L) was 100% at 24 h, and the yield of SAG was 94.2%. Molecular docking showed that the hypoglycemic activity of apigenin, apigenin-7-glucosides (AG), and SAG was mediated by binding with amino acids of α-glucosidase. The molecular docking results were verified by an in vitro anti-α-glucosidase assay and glucose consumption assay of active compounds. SAG had significant anti-α-glucosidase activity, with an IC50 of 0.485 mM and enhanced glucose consumption in HepG2 cells, which make it an excellent α-glucosidase inhibitor.

Perfectly Encoding π-Conjugated Anions in the RE5 (C3 N3 O3 )(OH)12 (RE=Y, Yb, Lu) Family with Strong Second Harmonic Generation Response and Balanced Birefringence.

Nonlinear optical (NLO) crystal, which simultaneously exhibits strong second-harmonic-generation (SHG) response and desired optical anisotropy, is a core optical material accessible to the modern optoelectronics. Accompanied by strong SHG effect in a NLO crystal, a contradictory problem of overlarge birefringence is ignored, leading to low frequency doubling efficiency and poor beam quality. Herein, a series of rare earth cyanurates RE5 (C3 N3 O3 )(OH)12 (RE=Y, Yb, Lu) were successfully characterized by 3D electron diffraction technique. Based on a "three birds with one stone" strategy, they enable the simultaneous fulfillment of strong SHG responses (2.5-4.2× KH2 PO4 ), short UV cutoff (ca. 220 nm) and applicable birefringence (ca. 0.15 at 800 nm) by the introduction of rare earth coordination control of π-conjugated (C3 N3 O3 )3- anions. These findings provide high-performance short-wavelength NLO materials and highlight the exploration of cyanurates as a new research area.

Anti-inflammatory and PTP1B inhibitory sesquiterpenoids from the twigs and leaves of Aglaia lawii.

Twelve sesquiterpenoids with seven different carbon skeletons, including four isodaucanes (1-4), an aromadendrane (5), a guaiane (6), a cadalane (7), two eudesmanes (8 and 9), two bisabolanes (10 and 11), and a megastigmane (12), were isolated from the twigs and leaves of Aglaia lawii (Wight) C. J. Saldanha et Ramamorthy. Of these compounds, amouanglienoids A (1) and B (2) are new isodaucane sesquiterpenoids. This is the first report of isodaucanes from the genus Aglaia, and amouanglienoid A (1) represents the first isodaucane containing a Δ7(8) double bond. Their structures were discerned from extensive spectroscopic analyses, single-crystal X-ray diffraction, and comparison of the experimental and calculated ECD data. In in vitro bioassays, compounds 1, 10, and 11 showed potent inhibitory effects against lipopolysaccharide (LPS)-induced inflammation in BV-2 microglial cells, while compound 11 exhibited considerable inhibition of PTP1B with an IC50 value of 16.05 ± 1.09 µM.

Realization of Enlarged Birefringence from BaCdBe2(BO3)2F2 to NaMgBe2(BO3)2F via the Cation Size Effect as a Potential Deep-Ultraviolet Birefringent Material.

Birefringence, as one of the most important factors for birefringent materials, governs their performances in applications. In this study, two previously unreported beryllium borates, BaCdBe2(BO3)2F2 (BDBBF) and NaMgBe2(BO3)2F (NMBBF), have been rationally designed by modulating interstitial cations. When smaller sizes of the cations are used, the crystal structure of NMBBF exhibits closer-packed 2D [Be6B6O12F3]∞ double layers rather than the 2D [Be3B3O6F3]∞ single layers in the crystal structure of BDBBF. The ultraviolet (UV) transmittance spectrum indicates that the short UV absorption edges of BDBBF and NMBBF are below 200 nm. The results from both theoretical calculations (theo.) and experimental characterizations (exp.) reveal enlarged birefringence from BDBBF (0.067 at 589 nm from theo. and 0.059 at 546.1 nm from exp.) to NMBBF (0.078 at 589 nm from theo. and 0.081 at 546.1 nm from exp.). Because of its excellent structure-based optical properties, NMBBF has the potential to be a deep-UV birefringent material. Our structural comparison and discussion provide a scope to aid in the design of potential deep-UV birefringent materials with large birefringence.

Structure, optical and luminescence properties of anhydrous samarium iodate Sm3(IO3)9(HIO3)4.

A new non-centrosymmetric iodate crystal Sm3(IO3)9(HIO3)4 has been successfully synthesized by a hydrothermal method. The crystal structure is a three-dimensional network with samarium polyhedra linked by iodate groups. It shows a moderate second harmonic generation response of 1.1 × KH2PO4 (KDP). The strongest emission in its luminescence spectrum is located at 600 nm under 403 nm excitation. Hence, Sm3(IO3)9(HIO3)4 is a potential orange laser material.

Mode selection in InGaAs/InGaAsP quantum well photonic crystal lasers based on coupled double-heterostructure cavities.

Photonic crystal lasers with a high-Q factor and small mode volume are ideal light sources for on-chip nano-photonic integration. Due to the submicron size of their active region, it is usually difficult to achieve high output power and single-mode lasing at the same time. In this work, we demonstrate well-selected single-mode lasing in a line-defect photonic crystal cavity by coupling it to the high-Q modes of a short double-heterostructure photonic crystal cavity. One of the FP-like modes of the line-defect cavity can be selected to lase by thermo-optically tuning the high-Q mode of the short cavity into resonance. Six FP-like modes are successively tuned into lasing with side mode suppression ratios all exceeding 15 dB. Furthermore, we show a continuous wavelength tunability of about 10 nm from all the selected modes. The coupled cavity system provides a remarkable platform to explore the rich laser physics through the spatial modulation of vacuum electromagnetic field at submicron scale.

Low loss modified Bezier bend waveguide.

We proposed and experimentally demonstrated a low loss modified Bezier bend for silicon and silicon nitride photonic integrated circuits. Both simulation and experimental results confirm that the modified Bezier bend can effectively reduce the bend loss for silicon and silicon nitride platform. At a bend radius of 1 µm, the reduction of bend loss from 0.367 dB/90° of circular bend and 0.35 dB/90° of traditional Bezier bend to 0.117 dB/90° of modified Bezier bend for silicon platform was experimentally demonstrated. For a 12-µm radius silicon nitride bend, the bend loss reduction from 0.65 dB/90° of circular bend and 0.575 dB/90° of traditional Bezier bend to 0.32 dB/90° was achieved. The proposed modified Bezier bend design can also be applied to other material systems, such as InP, LN, GaAs, etc., to effectively reduce the bend waveguide loss.

Design and analysis of an InGaAs/InGaAsP quantum well microlaser with longitudinal periodical strain distribution for single-mode lasing.

Single-mode lasing for small size semiconductor laser is significantly important in the on-chip optical signal processing, data storage, and dense optical integrated systems. This paper presents new, to the best of our knowledge, single-mode quantum well microlasers by distributing periodical strain along the longitudinal laser cavity. The quantum transmission line modeling (Q-TLM) method is employed to establish the model for strained microlasers. The dynamic output of quantum well microlasers with longitudinal periodical strain (LPS) distribution is analyzed in the time and frequency domains, and it is found that the introduction of LPS significantly improves the single-mode output of quantum well microlasers by increasing the side mode suppression ratio (SMSR) from 8.44 to 28.29 dB. The study results confirm that well-controlled periodical strain along the longitudinal laser cavity provides an alternative routine for realizing single-mode lasing by strain engineering.

Synthesis, Structure Determination, and Characterizations of a Polar Salt-Inclusion Scandium Germanate, Rb10Li3Sc4Ge12O36F.

A noncentrosymmetric salt-inclusion germanate, Rb10Li3Sc4Ge12O36F, was grown through spontaneous crystallization from a LiF-RbF flux. It crystallizes in the polar space group P31c with cell parameters of a = 10.7587(3) Å, c = 21.6691(10) Å, and Z = 2. Its structure features a complex 3D framework composed of helical [Ge4O12] chains from condensed [GeO4] tetrahedra running along the c axis, which are interconnected by the [ScO6] octahedra. Voids of the 3D net are filled with Rb+ ions, Li+ ions, and isolated trigonal-bipyramidal [Rb3Li2F] superalkali clusters. The title compound has a large band gap of 5.6 eV, a moderate powder second-harmonic-generation response of 0.9KDP, and an extremely small birefringence of 0.001, as was further unraveled by theoretical calculations.

PT symmetric single-mode line-defect photonic crystal lasers with asymmetric loss design.

The exploration of parity-time (PT) symmetry in micro-/nano-cavity lasers has recently gained immense research interest. The PT symmetric phase transition to single-mode lasing has been achieved by arranging the spatial distribution of optical gain and loss in single or coupled cavity systems. In terms of photonic crystal (PhC) lasers, a non-uniform pumping scheme is usually employed to enter the PT symmetry-breaking phase in a longitudinal PT symmetric system. Instead, we use a uniform pumping scheme to enable the PT symmetric transition to the desired single lasing mode in line-defect PhC cavities based on a simple design with asymmetric optical loss. The flexible control of gain-loss contrast is realized by removing a few rows of air holes in PhCs. We obtain single-mode lasing with a side mode suppression ratio (SMSR) of around 30 dB without affecting the threshold pump power and linewidth. The output power of the desired mode is six times higher than that in multimode lasing. This simple approach enables single-mode PhC lasers without sacrificing the output power, threshold pump power, and linewidth of a multimode cavity design.

Ca3(TeO3)2(MO4) (M = Mo, W): Mid-Infrared Nonlinear Optical Tellurates with Ultrawide Transparency Ranges and Superhigh Laser-Induced Damage Thresholds.

Intense interests in mid-infrared (MIR) nonlinear optical (NLO) crystals have erupted in recent years due to the development of optoelectronic applications ranging from remote monitoring to molecular spectroscopy. Here, two polar crystals Ca3(TeO3)2(MO4) (M = Mo, W) were grown from TeO2-MO3 flux by high-temperature solution methods. Ca3(TeO3)2(MoO4) and Ca3(TeO3)2(WO4) are isostructural, which feature novel structures consisting of asymmetric MO4 tetrahedra and TeO3 trigonal pyramids. Optical characterizations show that both crystals display ultrawide transparency ranges (279 nm to 5.78 µm and 290 nm to 5.62 µm), especially high optical transmittance over 80% in the important atmospheric transparent window of 3-5 µm, and superhigh laser damage thresholds (1.63 GW/cm2 and 1.50 GW/cm2), 54.3 and 50 times larger than that of state-of-the-art MIR NLO AgGaS2, respectively. Notably, they exhibit the widest band gaps and the loftiest laser-induced threshold damages among the reported tellurates so far. Moreover, Ca3(TeO3)2(MO4) exhibit type I phase matching at two working wavelengths owing to their large birefringence and strong second-harmonic generation responses from the distorted anions, as further elucidated by the first-principles calculations. The above characteristics indicate that Ca3(TeO3)2(MO4) crystals are high-performance MIR NLO materials, especially applying in high-power MIR laser operations.

BaZnBe2(BO3)2F2: a novel zinc-beryllium borate with SBBO-type structure overcoming the polymorphism problem.

A novel zinc-beryllium borate BaZnBe2(BO3)2F2 was grown by a high-temperature flux method for the first time. It crystallizes in P3[combining macron] with the cell parameters of a = b = 4.5998, c = 7.7037 and Z = 1, which is different from BaMBe2(BO3)2F2 (M = Mg, Ca). Interestingly, when Zn replaces Mg and Ca in BaMgBe2(BO3)2F2 and BaCaBe2(BO3)2F2, the structure retains the same anionic group but the symmetry is lowered. The title compound contains a flexible net structure [Be3B3O6F3]∞ in the a-b plane with Ba and Zn atoms located in the interlayers accordingly, which overcomes the structural instability problems of SrBe2B2O7 (SBBO). The structure evolution from SBBO to BaZnBe2(BO3)2F2 was discussed. This work is of great significance to the discovery of new materials and the modification of existing materials.

Widely tunable long-wave infrared difference frequency generation with a BaGa4Se7 crystal.

We report an experimental study of long-wave infrared difference frequency generation based on BaGa4Se7 crystal. The sources of two input wavelengths were the fundamental output of a Nd:YAG laser and its second-harmonic pumped ∼1.2µmKTiOPO4 optical parametric oscillator. A wide tuning range of 7.9-17.5 µm (>1.14 octave) was achieved, which reached the upper limit of the BaGa4Se7 transparency region. The spectra and pulse widths, input-output relationship, beam profile, wavelength tolerance, and angular acceptance of the phase-matching were characterized in detail. This presented coherent source can potentially be applied in multiple gas analyses and spectral imaging.

K4Cu3(C3N3O3)2X (X = Cl, Br): strong anisotropic layered semiconductors containing mixed p-p and d-p conjugated π-bonds.

2D materials are gaining more and more interest owing to their promising applications in future electronic industry. Here, two new quasi-2D metal cyanurates, K4Cu3(C3N3O3)2X (X = Cl, Br), were grown and characterized for the first time. They belong to the trigonal P3[combining macron]m1 space group and feature an infinite layer, constructed by p-p conjugation in the (C3N3O3) planar six-membered-rings and d-p conjugation in the N-Cu-N linear chains. Moreover, they are indirect semiconductors with suitable bandgaps of 3.5 eV, locating between g-C3N4 and h-BN. The electronic states and anisotropic optical responses were also studied through theoretical calculations.

Nonlinear-Optical Crystal Rb3YB6O12 with Condensed B5O10 Blocks That Exhibits an Intriguing Structural Arrangement and a Short Ultraviolet Absorption Edge.

Nonlinear-optical (NLO) crystals, which can regulate the laser wavelength through a cascading second-harmonic-generation technique, have been widely utilized in the field of optoelectronics. In this work, we grew the NLO borate crystal Rb3YB6O12 (RYBO) using the spontaneous crystallization method. RYBO crystallizes in a chiral trigonal space group of R32 with a new type of structural arrangement built from Y-O short chains and B5O10 groups. It is significantly different from the known structure of chemical analogues Rb3REB6O12 (RE = Nd, Eu) not only in the halved unit cell parameter but also in the Y-O connection manner. The NLO response of RYBO is about 0.8KDP, 8-fold larger than that of KB5O8·4H2O with the same B5O10 groups because of the coexistence of two NLO-active units of the distorted YO6 octahedra and B5O10 anions. Thanks to the short ultraviolet (UV) cutoff, RYBO may have potential NLO applications in the UV and even deep-UV spectral regions.