Localized self-assembly of macroscopically structured supramolecular hydrogels through reaction-diffusion.

Localized molecular self-assembly has been developed as an effective approach for the fabrication of spatially resolved supramolecular hydrogels, showing great potential for many high-tech applications. However, the fabrication of macroscopically structured supramolecular hydrogels through molecular self-assembly remains a challenge. Herein, we report on localized self-assembly of low molecular weight hydrogelators through a simple reaction-diffusion approach, giving rise to various macroscopically patterned supramolecular hydrogels. This is achieved on the basis of an acid-catalyzed hydrazone supramolecular hydrogelator system. The acid was pre-loaded in a polydimethylsiloxane (PDMS) substrate, generating a proton gradient in the vicinity of the PDMS surface after immersing the PDMS in the aqueous solution of the hydrogelator precursors. The acid dramatically accelerates the in situ formation and self-assembly of the hydrazone hydrogelators, leading to localized formation of supramolecular hydrogels. The growth rate of the supramolecular hydrogels can be easily tuned through controlling the concentrations of the hydrogelator precursors and HCl. Importantly, differently shaped supramolecular hydrogel objects can be obtained by simply changing the shapes of PDMS. This work suggests that reaction-diffusion-mediated localized hydrogelation can serve as an approach towards macroscopically structuralized supramolecular hydrogels, which may find potential applications ranging from tissue engineering to biosensors.

Mixed Alkali Metal and Alkaline Earth Metal Scandium Borate Birefringence Material with Layered Structure and Short Ultraviolet Cutoff Edge.

Birefringent crystals are essential in the domains of linear and nonlinear optics that need light wave polarization control. Rare earth borate has become a popular study material for ultraviolet (UV) birefringence crystals due to its short cutoff edge in the UV area. RbBaScB6O12, a two-dimensional layered structure compound with the B3O6 group, was effectively synthesized through spontaneous crystallization. The UV cutoff edge of RbBaScB6O12 is shorter than 200 nm, and the experimental birefringence is 0.139 @ 550 nm. Theoretical research indicates that the large birefringence originates from the synergistic impact of the B3O6 group and the ScO6 octahedron. RbBaScB6O12 is an outstanding candidate material for birefringence crystals in the UV and even deep UV regions due to its short UV cutoff edge and significant birefringence.

Structure and Optical Properties of LixAg1-xGaSe2 and LixAg1-xInSe2.

Complete substitution of Li atoms for Ag atoms in AgGaSe2 and AgInSe2 was achieved, resulting in the solid solutions LixAg1-xGaSe2 and LixAg1-xInSe2. The detailed crystal structures were determined by single-crystal X-ray diffraction and solid-state 7Li nuclear magnetic resonance spectroscopy, which confirm that Li atoms occupy unique sites and disorder only with Ag atoms. The tetragonal CuFeS2-type structure (space group I4̅2d) was retained within the entirety of the Ga-containing solid solution LixAg1-xGaSe2, which is noteworthy because the end-member LiGaSe2 normally adopts the orthorhombic ß-NaFeO2-type structure (space group Pna21). These structures are closely related, being superstructures of the cubic sphalerite and hexagonal wurtzite prototypes adopted by diamond-like semiconductors. For the In-containing solid solution LixAg1-xInSe2, the structure transforms from the tetragonal to orthorhombic forms as the Li content increases past x = 0.50. The optical band gaps increase gradually with higher Li content, from 1.8 to 3.4 eV in LixAg1-xGaSe2 and from 1.2 to 2.5 eV in LixAg1-xInSe2, enabling control to desired values, while the second harmonic generation responses become stronger or are similar to those of benchmark infrared nonlinear optical materials such as AgGaS2. All members of these solid solutions remain congruently melting at accessible temperatures between 800 and 900 °C. Electronic structure calculations support the linear trends seen in the optical band gaps and confirm the mostly ionic character present in Li-Se bonds, in contrast to the more covalent character in Ga-Se or In-Se bonds.

Weyl semimetal mediated epsilon-near-zero hybrid polaritons and the induced nonreciprocal radiation.

Polaritonic excitation and management in ultra-thin polar crystals has recently received significant attention and holds new promise for epsilon-near-zero (ENZ) modes. However, manipulation of the ENZ mode via anisotropic magneto-optic (MO) material remains elusive. Herein, we provide an effective strategy for constructing an ENZ polar thin film with dependence on Weyl semimetals (WSM). The thermal radiation of the proposed device is explored with electromagnetic (EM) simulations that utilize the anisotropic rigorous coupled-wave analysis (aRCWA) method. Strong coupling of the ENZ mode to WSM polaritons has been demonstrated, and the structural parameters hold tolerance on the order of hundreds of nanometers, which is highly favorable for low-cost fabrication and high-performance application. By changing both the azimuthal angle (ϕ) and angle of incidence (θ), the nonreciprocity (η) can be effectively influenced. The distribution of η is symmetrical with ϕ = 180°, η = 0 when ϕ = 90° and ϕ = 270°. The mechanism of this proposal is owing to the hybrid polaritons supported by the polar thin film and nonreciprocal radiation of WSM, which is validated by examining the amplitude distribution of the magnetic field. The nonreciprocal emitter described herein allows simultaneous control of spectral distribution and polarization of radiation, which will facilitate the active design and application of mid-infrared (MIR) thermal emitters.

The Kurtz-Perry Powder Technique Revisited: A Study of the Effect of Reference Selection on Powder Second-Harmonic Generation Response.

The accurate evaluation of nonlinear optical (NLO) coefficient, the main parameter affecting light conversion efficiency, plays a crucial role in the development of NLO materials. The Kurtz-Perry powder technique can evaluate second-harmonic generation (SHG) intensity in pristine powder form, saving a significant amount of time and energy in the preliminary screening of materials. However, the Kurtz-Perry method has recently been subject to some controversy due to the limitations of the Kurtz-Perry theory and the oversimplified experimental operation. Therefore, it is very meaningful to revisit and develop the Kurtz-Perry technique. In this work, on the basis of introducing the light scattering effect into the original Kurtz-Perry theory, the theoretical expression of second-harmonic generation intensity with respect to band gap and refractive index are analyzed. In addition, the reference-dependent SHG measurements were carried out on polycrystalline LiB3O5 (LBO), AgGaQ2 (Q = S, Se), BaGa4Q7 (Q = S, Se), and ZnGeP2 (ZGP), and the results of SHG response emphasize the importance of using appropriate references to the Kurtz-Perry method. In order to obtain reliable values of nonlinear coefficients, two criteria for selecting a reference compound were proposed: (1) it should possess a band gap close to that of the sample to be measured and (2) it should possess a refractive index close to that of the sample to be measured. This work might shed light on improvements in accuracy that can be made for effective NLO coefficients obtained using the Kurtz-Perry method.

Synthesis and Characterizations of Two Tellurides ß-BaGa2Te4 and Ba5Ga2Ge3Te12 with Flexible Chain Structure.

Demands for IR birefringent materials are increasing due to the rapid developments of IR laser applications. Herein, two new chain tellurides ß-BaGa2Te4 and Ba5Ga2Ge3Te12 have been discovered. ß-BaGa2Te4 crystallizes in the orthorhombic space group Imma (no. 74) with unit cell constants of a = 23.813(3) Å, b = 11.9673(19) Å, and c = 6.7215(9) Å, while Ba5Ga2Ge3Te12 crystallizes in the monoclinic space group P21/c (no. 14) with unit cell constants of a = 13.6540(3) Å, b = 9.6705(2) Å, and c = 23.1134(7) Å. The structure of ß-BaGa2Te4 can be considered to be the antiparallel arrangement of one-dimensional (1D) [GaTe2] chains formed by edge-sharing GaTe4 tetrahedra, which are separated by Ba2+ cations. In the crystal structure of Ba5Ga2Ge3Te12, two kinds of 1D chains, namely chain 1 ∞1[(GaGe)3Te8] and chain 2 ∞1[(GaGe)2Te4], are stacked alternately and put together by the coulomb force with Ba2+ cations. In addition, First-principles calculations indicate that ß-BaGa2Te4 has a large birefringence, ∼0.325 at 2050 nm, derived from the superposition of the polarizabilities of GaTe4 tetrahedra, implying that it has potential as an IR birefringent material. This work may provide some guidance for exploring new IR birefringent crystals.

Synthesis and characterization of a new rare earth borate nonlinear optical crystal K7PbLu2B15O30.

A new complex rare earth borate K7PbLu2B15O30 was prepared by the spontaneous crystallization method. K7PbLu2B15O30 is crystallized in the chiral trigonal space group R32 with cell parameters a = b = 13.0893(3) Å, c = 15.2379(6) Å, α = ß = 90°, γ = 120°, and Z = 3. The basic structure of the crystal can be seen as composed of B5O10 groups and LuO6 polyhedra sharing oxygen atoms, while K+ and Pb2+ fill the space to balance the charge. The UV transmission cut-off edge of K7PbLu2B15O30 was less than 300 nm, and the powder SHG response was roughly 1.1 times that of KDP. Furthermore, a first-principles analysis was performed to see more about the relationship between the crystal structure and optical characteristics.

Bridging oxygen atoms in trigonal prism units driven strong second-harmonic-generation efficiency in Sr3Ge2O4Te3.

Herein, a novel IR NLO oxytelluride Sr3Ge2O4Te3 was successfully designed and synthesized through a "partial O-to-Te substitution" strategy. Compared with the parent oxide, Sr3Ge2O4Te3 not only successfully achieves a phase-matchability transition (from NPM to PM), but also greatly improves the linear and NLO performances, including a wide band gap (2.26 eV), strong SHG response (1.3 × AgGaSe2) and large optical anisotropy (Δn = 0.152@2090 nm). The analyses of the structure-property relationship and SHG-density indicate that the bridging oxygen in the [O3Ge-O-GeTe3] prism unit plays the most important role in the multiplication SHG effect. This work provides some insights into the design and exploration of novel IR NLO materials.