Twist Phase Matching in Two-Dimensional Materials.

Optical phase matching involves establishing a proper phase relationship between the fundamental excitation and generated waves to enable efficient optical parametric processes. It is typically achieved through birefringence or periodic polarization. Here, we report that the interlayer twist angle in two-dimensional (2D) materials creates a nonlinear geometric phase that can compensate for the phase mismatch, and the vertical assembly of the 2D layers with a proper twist sequence generates a nontrivial "twist-phase-matching" (twist-PM) regime. The twist-PM model provides superior flexibility in the design of optical crystals, which can be applied for twisted layers with either periodic or random thickness distributions. The designed crystal from the twisted rhombohedral boron nitride films within a thickness of only 3.2 µm is capable of producing a second-harmonic generation with conversion efficiency of ∼8% and facile polarization controllability that is absent in conventional crystals. Our methodology establishes a platform for the rational design and atomic manufacturing of nonlinear optical crystals based on abundant 2D materials.

Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3: A Great Enhancement in Birefringence Induced by Optimal Arrangement of π-Conjugated [BO3] Units.

In virtue of the essential role in controlling polarized light, outstanding ultraviolet (UV) and deep-ultraviolet (DUV) birefringent crystals are imperative in many advanced optical instruments. To design the UV and DUV crystals with large birefringence, we paid more attention to combining the excellent gene, π-conjugated [BO3] unit and metal cations beneficial to blue-shift the cutoff edge; finally, two rare-earth borates Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3 have been synthesized using the high-temperature solution method. Compared with Na3La2(BO3)3, Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3 are isostructural, and the isolated [BO3] units are arranged nearly parallel to each other in the structure, which is conducive to generating a larger birefringence. The structural comparison between the two crystals and Na3La2(BO3)3 indicates that the various coordination environments of alkali metal cations play an important role in the evolution of the crystal structure from Li3La2(BO3)3 and Li1.75Na1.25La2(BO3)3 to Na3La2(BO3)3. This work can contribute to a better understanding of the enhancement in birefringence from Na3La2(BO3)3 (0.023 @ 1064 nm) to Li3La2(BO3)3 (0.078 @ 1064 nm) with the perspective of structure-property relationships. Meanwhile, the two title crystals possess the DUV cutoff edge (<190 nm), suggesting that they can be applied as the DUV birefringent crystals.

Hydroxyfluorooxoborate Na[B3 O3 F2 (OH)2 ]⋠[B(OH)3 ]: Optimizing the Optical Anisotropy with Heteroanionic Units for Deep Ultraviolet Birefringent Crystals.

Maximizing the optical anisotropy in birefringent materials has emerged as an efficient route for modulating the polarization-dependent light propagation. Currently, the generation of deep-ultraviolet (deep-UV) polarized light below 200 nm is essential but challenging due to the interdisciplinary significance and insufficiency of high-performing birefringent crystals. Herein, by introducing multiple heteroanionic units, the first sodium difluorodihydroxytriborate-boric acid Na[B3 O3 F2 (OH)2 ]⋅[B(OH)3 ] has been characterized as a novel deep-UV birefringent crystal. Two rare heteroanionic units, [B3 O3 F2 (OH)2 ] and [B(OH)3 ], optimally align to induce large optical anisotropy and also the dangling bonds are eliminated with hydrogens, which results in an extremely large birefringence and band gap. The well-ordered OH/F anions in [B3 O3 F2 (OH)2 ] and [B(OH)3 ] were identified and confirmed by various approaches, and also the origin of large birefringence was theoretically discussed. These results confirm the feasibility of utilizing hydrogen involved heteroanionic units to design crystals with large birefringence, and also expand the alternative system of deep-UV birefringent crystals with new hydroxyfluorooxoborates.

Transcriptomic analysis reveals mechanism of light-sensitive albinism in tea plant Camellia sinensis 'Huangjinju'.

BACKGROUND: Camellia sinensis 'Huangjinju' is an albino tea variety developed recently in China. Young leaves of 'Huangjinju' demonstrate bright yellow when cultivated under natural sunlight, but regreens under reduced light intensity. To elucidate the physiological and molecular mechanisms of this light-sensitive albinism, we compared leaf pigmentation, metabolites, cellular ultrastructure and transcriptome between plants cultured under natural sunlight and shade. RESULTS: Shading treatment doubled the chlorophyll concentration and regreened albino leaves; carotenoid also increased by 30%. Electron microscopy analyses showed that chloroplast not only increased in number but also in size with a complete set of components. In addition, regreened leaves also had a significantly higher concentration of polyphenols and catechins than albino leaves. At transcriptomic level, a total of 507 genes were differentially expressed in response to light condition changes. The most enriched pathways include light harvest protein complex, response to stimuli, oxidation-reduction process, generation of precursor metabolites and energy response. CONCLUSION: The integrated strategy in this study allows a mechanistic understanding of leaf albinism in light-sensitive tea plants and suggested the regulation of gene networks involved in pigmentation and protein processing. Results from this study provide valuable information to this area and can benefit the domestication and artificial breeding to develop new albino tea varieties.

Stacking-Controlled Growth of rBN Crystalline Films with High Nonlinear Optical Conversion Efficiency up to 1.

Nonlinear optical crystals lie at the core of ultrafast laser science and quantum communication technology. The emergence of 2D materials provides a revolutionary potential for nonlinear optical crystals due to their exceptionally high nonlinear coefficients. However, uncontrolled stacking orders generally induce the destructive nonlinear response due to the optical phase deviation in different 2D layers. Therefore, conversion efficiency of 2D nonlinear crystals is typically limited to less than 0.01% (far below the practical criterion of >1%). Here, crystalline films of rhombohedral boron nitride (rBN) with parallel stacked layers are controllably synthesized. This success is realized by the utilization of vicinal FeNi (111) single crystal, where both the unidirectional arrangement of BN grains into a single-crystal monolayer and the continuous precipitation of (B,N) source for thick layers are guaranteed. The preserved in-plane inversion asymmetry in rBN films keeps the in-phase second-harmonic generation field in every layer and leads to a record-high conversion efficiency of 1% in the whole family of 2D materials within the coherence thickness of only 1.6 µm. The work provides a route for designing ultrathin nonlinear optical crystals from 2D materials, and will promote the on-demand fabrication of integrated photonic and compact quantum optical devices.

Hepatoprotective effects of different mulberry leaf extracts against acute liver injury in rats by alleviating oxidative stress and inflammatory response.

This study investigated the hepatoprotective effects of various mulberry (Morus alba L.) leaf extracts (MLEs), including mulberry ethanol extract (MEE), aqueous extract (MAE) and a combination extract (MCE) against D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced acute liver injury in rats. It aimed to explore the possible molecular mechanism of the liver-protecting function of mulberry leaves and provide a reference for choosing the appropriate extraction method. The results showed that the three extracts contained different amounts of phenolic compounds, 1-deoxynojirimycin (DNJ) and polysaccharides. MLEs markedly improved the pathological status of rat liver tissue, decreased the levels of AST, ALT, TNF-α, IL-1ß, IL-6 and MDA, while increased the levels of GSH, SOD and CAT in the D-GalN/LPS-treated rats at the same time. MEE, with the highest amount of total phenolics, exhibited the highest antioxidant activity corresponding to the protein expression level of Nrf2 and HO-1. MCE significantly suppressed the expression of apoptosis-related dot-like protein (ASC) and Caspase-1 and inhibited the phosphorylation of p38 MAPK and ERK1/2, thereby showing high anti-inflammatory activity. These results indicated that the active components from mulberry leaves protected rats against acute liver injury, attributed to a reduction in both oxidative stress and inflammatory response. The protective effect may be implicated in regulating the Nrf2, NLRP3 and MAPK signaling pathways.

Noncentrosymmetric Rare-Earth Borate Fluoride La2B5O9F3: A New Ultraviolet Nonlinear Optical Crystal with Enhanced Linear and Nonlinear Performance.

In crystal engineering, it is an effective and controllable approach to modify the electronic band structure and optimize crystal performances using rational chemical cosubstitution in a classic structure model. Herein, the noncentrosymmetric (NCS) rare-earth borate fluoride La2B5O9F3 was designed and synthesized successfully based on the extraordinarily stable M2B5O9X (M = Ca, Sr, Ba, Sn, Pb, and Eu; X = Cl, Br, and I) template. Moreover, all 70 rare-earth borate halides were discussed, and the ratio of crystallization in NCS group is only 17.1%, much lower than 34.9% in all anhydrous borates. Benefiting from the substitution of [MOX] by [LaOF] polyhedra with improved hyperpolarizability and anisotropy of polarizability, compared with the M2B5O9X family, La2B5O9F3 with optimized band structure exhibits the suitable SHG response (1.2 × KH2PO4 (KDP) @ 1064 nm), large band gap (6.58 eV), and moderate birefringence, which well achieves the optimal balance among the three critical parameters mentioned above for nonlinear optical (NLO) applications in the short-wavelength region. This work expands the research field of NLO materials to rare-earth borate fluorides and can lead to a better understanding of the role of rare-earth metal cations.