A large nonlinear optical (NLO) coefficient and a wide band gap are two crucial but contradictory parameters that are difficult to achieve simultaneously in a single infrared (IR) NLO compound. A ...salt‐inclusion chalcogenide (SIC), LiLiCs2ClGa3S6 (1), was prepared that presents a nanosized tunnel framework constructed from monotype chalcogenide tetrahedra. Highly oriented covalent GaS4 tetrahedra in the host lead to a moderate second harmonic generation response (0.7 AgGaS2), and ionic guests effectively broaden the band gap to the widest value (4.18 eV) among all IR NLO chalcogenides, thereby achieving a remarkable balance between NLO efficiency and band gap.
The salt‐inclusion chalcogenide LiLiCs2ClGa3S6 is presented, which features a 3D framework composed of Ga3S6 nanosized tunnels. Introduction of an ionic guest to the covalent chalcogenide host produces a material with a moderate nonlinear optical (NLO) coefficient and an ultrawide band gap (Eg). These characteristics are promising for the development of infrared (IR) NLO materials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Extending photoresponse ranges of semiconductors to the entire ultraviolet-visible (UV)-shortwave near-infrared (SWIR) region (ca. 200-3000 nm) is highly desirable to reduce complexity and cost of ...photodetectors or to promote power conversion efficiency of solar cells. The observed up limit of photoresponse for organic-based semiconductors is about 1800 nm, far from covering the UV-SWIR region. Here we develop a cyanide-bridged layer-directed intercalation approach and obtain a series of two viologen-based 2D semiconductors with multispectral photoresponse. In these compounds, infinitely π-stacked redox-active N-methyl bipyridinium cations with near-planar structures are sandwiched by cyanide-bridged Mn
-Fe
or Zn
-Fe
layers. Radical-π interactions among the infinitely π-stacked N-methyl bipyridinium components favor the extension of absorption range. Both semiconductors show light/thermo-induced color change with the formation of stable radicals. They have intrinsic photocurrent response in the range of at least 355-2400 nm, which exceeds all reported values for known single-component organic-based semiconductors.
A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced ...damage threshold (LIDT). Herein we report the preparation of a new Ga2Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59–25 μm is also significantly wider than that of AGS (ca. 0.48–≈11.4 μm). The occurrence of the strong SHG responses and good phase‐matching indicate that the structure of the new Ga2Se3 phase can only be non‐centrosymmetric and have a lower symmetry than the cubic γ‐phase. The observed excellent SHG and phase‐matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.
A simple but perfect case: A new phase of gallium selenides (δ‐Ga2Se3) has been obtained via solid‐state reactions. δ‐Ga2Se3 is phase‐matchable with large second harmonic generation (SHG) responses, high laser‐induced damage thresholds (LIDTs), and wide transparent range of 0.59–25 μm. These properties are all required for the application of NLO materials with high‐power lasers.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A
bstract
In this paper, we reduce the electromagnetic theory to future null infinity and obtain a vector theory at the boundary. We compute the Poincaré flux operators which could be generalized. We ...quantize the vector theory, and impose normal order on the extended flux operators. It is shown that these flux operators generate the supertranslation and superrotation. When work out the commutators of these operators, we find that a generalized electromagnetic duality operator should be included as the generators to form a closed symmetry algebra.
A
bstract
We reduce the gravitational theory in an asymptotically flat spacetime to future null infinity. We compute the Poincaré flux operators at future null infinity and construct the ...supertranslation and superrotation generators. The generators are shown to form a closed symmetry algebra by including a generalized gravitational duality operator. We could regard all the generators as the Hamiltonians with respect to the symmetry transformation in the boundary field theory. Our construction of the generators may relate to the BMS fluxes defined in the literature by adding counterterms to the Bondi mass and angular momentum aspects.
Exploring nonlinear optical (NLO) functional motifs (FM, the structural origin of NLO efficiency) is vital for the rational design of NLO materials. Normal spectrum techniques applied in studying ...photon exciting materials are invalid for NLO materials, in which electrons are not excited substantially but only distorted under laser. A general strategy of determining NLO FM is proposed by comparative studies of experimental electron density (ED) without and under the laser. The in situ experimental ED and wavefunction of typical NLO material LiB3O5 (LBO) under dark and 360 and 1064 nm lasers are investigated. Compared with the initial state under dark, the ED of B3O5− unit at functional states under laser irradiation exhibits remarkable changes of topological atomic and bond properties, confirming the NLO FM being B3O5−. The work extracts for the first time the FM of a NLO material experimentally and highlights the crucial role of in situ ED analysis in studying NLO mechanisms.
A general strategy of determining nonlinear optical (NLO) functional motif (FM) is proposed by comparative studies of experimental electron density (ED) without and under the laser. In situ ED analysis is firstly adopted for an NLO material with typical LiB3O5 as an example. The work extracts the FM of a NLO material experimentally and highlights the crucial role of in situ ED analysis in studying NLO mechanisms.
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The typical chalcopyrite AgGaQ2 (Q = S, Se) are commercial infrared (IR) second‐order nonlinear optical (NLO) materials; however, they suffer from unexpected laser‐induced damage thresholds (LIDTs) ...primairy due to their narrow band gaps. Herein, what sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, represented by SZn4S12 + S4Zn13S24 + 11ZnS4 ⇒ MS12+ M4ClS24 + 11GaS4, in which the covalent SxZny units in the diamond‐like sphalerite ZnS are synergistically replaced by cationic MxCly units, resulting in two novel salt‐inclusion sulfides, MM4ClGa11S20 (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS4 anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS2, facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS2@1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second‐harmonic generation intensities (0.84 and 0.78 × AgGaS2@2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS4 units. Importantly, this study demonstrates the successful application of the cationic substitution strategy based on diamond‐like structures to provide a feasible chemical design insight for constructing high‐performance NLO materials.
What sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, offers two excellent infrared nonlinear optical materials, which provides a feasible chemical design insight for constructing high‐performance nonlinear optical materials.
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The randomly‐oriented glass fibers (GF) reinforced composites with Bisphenol A–amine based benzoxazine (BA‐a) and bio‐based eugenol‐based phthalonitrile (EPN) copolymer were developed by an ...isothermal compression molding technique. The silane coupling agent‐treated GF (TGF) reinforced composites showed much better impact strength as compared to as‐received GF reinforced composites. A rise of 95.2 MPa, 5.5GPa, 69.1 MPa, and 2.5GPa in flexural strength, flexural modulus, tensile strength, and Young's modulus were observed, respectively. The DMA results confirmed that the storage modulus (E') and glass transition temperature (Tg) were gradually increased and the damping factor decreased as the TGF reinforcement was raised from 0 to 40 wt%. E' and Tg values were 3.09 GPa and 27°C, respectively, higher than the recorded values for the neat copolymer. The 40 wt% TGF reinforced poly(BA‐a/EPN) composite showed the maximum thermal stability values of 475.4, 507.3°C, and 75.43% for T5, T10, and Yc, respectively. The LOI values confirm that the TGF/copolymer composites have self‐extinguishing properties.
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