Zheshuai Lin

NaSr3Be3B3O9F4: a promising deep-ultraviolet nonlinear optical material resulting from the cooperative alignment of the [Be3B3O12F](10-) anionic group.

The demand for deep-ultraviolet (deep-UV) coherent light sources (l< 200 nm) has become increasingly urgent because they have important applications in semiconductor photolithography, laser micromachining, modern scientific instruments (super-high-resolution and angle-resolved photoemission spectrometer, for example) and so forth. To date, the most effective method to generate deep-UV coherent light with solid-state lasers is through cascaded frequency conversion, in particular multiharmonics, using deep-UV nonlinear optical (NLO) crystals. Therefore, the discovery of suitable deep-UV NLO crystals is of great importance. In the past decades, the anionic group theory, which reveals that the overall nonlinearity of a crystal is the geometrical superposition of the microscopic second-order susceptibility tensors of the NLO-active anionic groups, has been very successful in developing borate NLO crystals. Several important NLO crystals have been discovered, including b-BaB2O4 (BBO), [4] LiB3O5 (LBO), [5] CsB3O5 (CBO), CsLiB6O10 (CLBO), [7, 8] and YCa4O(BO3)3 (YCOB), which have been widely used in NLO optics. However, they cannot be used to generate deep-UV coherent light (l< 200 nm) by multiharmonic generation owing to some inherent shortcomings. Thus, the search for new NLO materials, particularly for deep-UVapplications, has attracted considerable attention. A deep-UV NLO material must have a very short absorption edge, and in this respect, beryllium borates are attractive as they are supposed to possess very large energy gap. It is also well known that the incorporation of fluorine can effectively cause the UV absorption edge of a crystal to blue-shift, so our group has made great efforts to search for new deep-UV NLO fluorine beryllium borate crystals. After more than ten years of intensive research in our group, the KBe2BO3F2 [16–18] (KBBF) crystal became the first practically usable deep-UV NLO crystal used to generate coherent 177.3 and 193 nm light. The excellent NLO properties of KBBF crystals are mainly determined by the (Be2BO3F2)1 layer made up of trigonal-planar [BO3] units and the tetrahedral [BeO3F] units. This deep-UV coherent light material has been used as a photon source in modern instruments and revealed many novel scientific phenomena which could not be observed by traditional techniques, as shown in the study of superconductor CeRu2 [19] and Bi2Sr2CaCu2O8+d. [20] Unfortunately, the KBBF crystal is very difficult to grow in thickness because of its strong layering tendency, which severely limits the coherent output power. Therefore, there is great demand for new types of fluorine beryllium borates which have deepUV transmission, moderate birefringence, and relatively large second harmonic generation (SHG) coefficients, and at the same time overcome the crystal-growth problems found in the KBBF crystal. Alkali-metal and alkaline-earth-metal cations are favorable for the transmission of UV light because there are no d–d electron or f–f electron transitions in this spectral region. As shown in numerous explorations, the size and charge of cations have great influence on the macroscopic packing of anions, which in turn determines the overall NLO properties in a crystal. 22] Herein, we utilize both alkali-metal and alkaline-earth-metal cations. Different charge/size combinations of mixed cations may have different influences on the packing of anions, so it is more likely to isolate new phases with interesting stoichiometries, structures, and properties. To date, no fluorine beryllium borates with mixed cations have been reported. Guided by this idea, we successfully obtained a new alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4, which contains the novel anionic group [Be3B3O12F] 10 as the basic building unit. Furthermore, the arrangement of these [Be3B3O12F] 10 groups is very favorable for generating large a NLO response and moderate birefringence and especially for avoiding the layering tendency during bulk crystal growth. Herein, we report the synthesis, crystal growth, structure, linear and nonlinear optical properties, thermal behavior, and electronic structure of NaSr3Be3B3O9F. These results indicate that the NaSr3Be3B3O9F4 crystal may be a promising NLO material in the deep-UV range. NaSr3Be3B3O9F4 [23] crystallizes in the noncentrosymmetric trigonal space group R3m. The crystal structure is depicted in Figure 1a. In the asymmetric unit, Sr, Na, Be, B each occupy one crystallographically unique position, and there are two unique F and O positions. The B atom is coordinated to three O atoms to form a planar BO3 unit with B O bond lengths [*] H. Huang, J. Yao, Z. Lin, X. Wang, R. He, W. Yao, N. Zhai, Prof. C. Chen Center for Crystal Research and Development Technical Institute of Physics and Chemistry Chinese Academy of Sciences, Beijing 100190 (China) E-mail: cct@mail.ipc.ac.cn

Beryllium-free Li4Sr(BO3)(2) for deep-ultraviolet nonlinear optical applications

Nonlinear optical (NLO) materials are of great importance in laser science and technology, as they can expand the wavelength range provided by common laser sources. Few NLO materials, except KBe2BO3F2 (KBBF), can practically generate deep-ultraviolet coherent light by direct second-harmonic generation process, limited by the fundamental requirements on the structure-directing optical properties. However, KBBF suffers a strong layering tendency and high toxicity of the containing beryllium, which hinder the commercial availability of KBBF. Here we report a new beryllium-free borate, Li4Sr(BO3)2, which preserves the structural merits of KBBF, resulting in the desirable optical properties. Furthermore, Li4Sr(BO3)2 mitigates the layering tendency greatly and enhances the efficiency of second-harmonic generation by more than half that of KBBF. These results suggest that Li4Sr(BO3)2 is an attractive candidate for the next generation of deep-ultraviolet NLO materials. This beryllium-free borate represents a new research direction in the development of deep-ultraviolet NLO materials.

BaGa4Se7: A New Congruent-Melting IR Nonlinear Optical Material

The new compound BaGa(4)Se(7) has been synthesized for the first time. It crystallizes in the monoclinic space group Pc with a = 7.6252 (15) Å, b = 6.5114 (13) Å, c = 14.702 (4) Å, β = 121.24 (2)°, and Z = 2. In the structure, GaSe(4) tetrahedra share corners to form a three-dimensional framework with cavities occupied by Ba(2+) cations. The material is a wide-band gap semiconductor with the visible and IR optical absorption edges being 0.47 and 18.0 μm, respectively. BaGa(4)Se(7) melts congruently at 968 °C and exhibits a second harmonic generation response at 1 μm that is approximately 2-3 times that of the benchmark material AgGaS(2). A first-principles calculation of the electronic structure, linear and nonlinear optical properties of BaGa(4)Se(7) was performed. The calculated birefractive indexΔn = 0.08 at 1 μm and the major SHG tensor elements are: d(11) = 18.2 pm/V and d(13) = -20.6 pm/V. This new material is a very promising NLO crystal for practical application in the IR region.

A new cathode material for super-valent battery based on aluminium ion intercalation and deintercalation

Due to their small footprint and flexible siting, rechargeable batteries are attractive for energy storage systems. A super-valent battery based on aluminium ion intercalation and deintercalation is proposed in this work with VO2 as cathode and high-purity Al foil as anode. First-principles calculations are also employed to theoretically investigate the crystal structure change and the insertion-extraction mechanism of Al ions in the super-valent battery. Long cycle life, low cost and good capacity are achieved in this battery system. At the current density of 50 mAg−1, the discharge capacity remains 116 mAhg−1 after 100 cycles. Comparing to monovalent Li-ion battery, the super-valent battery has the potential to deliver more charges and gain higher specific capacity.

Nonlinear Optical Borate Crystals, Principles and Applications

Preface INTRODUCTION History of the Theoretical Understanding for Nonlinear Optical Crystals History of Development on Nonlinear Optical Borate Crystals Crystal Growth of Nonlinear Borate Crystals and Current Status of Applications THEORETICAL BASIS TO DEVELOP BORATE NONLINEAR OPTICAL CRYSTALS BORATE NONLINEAR OPTICAL CRYSTALS FOR FREQUENCY CONVERSION BBO LBO Family KBBF Family Other Borate Crystals Borate Crystals in Developing APPLICATIONS Rapid Proto-Typing Semiconductor Industry - Bia-Hole Drilling - Annealing - Marking - Inspection Bio-Medical Applications - Eye Surgery - Protein Processing Advanced Instrument Making

Beryllium-Free Rb3Al3B3O10F with Reinforced Interlayer Bonding as a Deep-Ultraviolet Nonlinear Optical Crystal

A new beryllium-free borate Rb3Al3B3O10F has been synthesized and characterized by single-crystal X-ray diffraction. It features a framework structure consisting of alveolate [Al3(BO3)3OF]∞ layers tightly bound via Al-O and Al-F bridged bonds, with the in-layer [BO3](3-) groups in nearly coplanar and aligned arrangement. This compound is transparent down to 200 nm and is phase-matchable with a powder second-harmonic generation efficiency of 1.2 times that of KH2PO4. Remarkably, it exhibits a strong interlayer bonding which is about one order larger than that of the benchmark KBe2BO3F2, thus no layering tendency was observed during the crystal growth. In addition, it is nonhygroscopic and thermally stable up to ∼1462 K. These attributes make Rb3Al3B3O10F a promising nonlinear optical crystal in the deep-ultraviolet region. First-principles calculations, combined with the anionic group theory, were adopted to rationalize the optical properties.

Microspheric Na2Ti3O7 consisting of tiny nanotubes: an anode material for sodium-ion batteries with ultrafast charge–discharge rates

Conventionally, rechargeable batteries with a fast charge-discharge rate, while being able to be implemented in large-scale applications with low prices, are critical for new energy storage systems. In this work, first-principles simulations were employed to theoretically investigate the insertion of sodium into the Na(2)Ti(3)O(7) structure. The result discovered that the theoretical capacity of Na(2)Ti(3)O(7) was 311 mA h g(-1). Furthermore, a microspheric Na(2)Ti(3)O(7) material consisting of tiny nanotubes of ca. 8 nm in outside diameter and a few hundred nanometers in length has been synthesized. The galvanostatic charge-discharge measurements, using the as-prepared Na(2)Ti(3)O(7) nanotubes as a working electrode with a voltage range of 0.01-2.5 V vs. Na(+)/Na, disclosed that a high capacity was maintained even under an ultrafast charge-discharge rate. At a current density of 354 mA g(-1), the discharge capacity was maintained at 108 mA h g(-1) over 100 cycles. Even at a very large current density of 3540 mA g(-1), the discharge capacity was still 85 mA h g(-1). HRTEM analysis and electrochemical tests proved that sodium ions could not only intercalate into the Na(2)Ti(3)O(7) crystal, but could also be stored in the intracavity of the nanotubes. All of the results disclose that the as-prepared Na(2)Ti(3)O(7) nanotubes are able to be used as anode materials in large-scale applications for rechargeable sodium-ion batteries at low cost while maintaining excellent performance.

Mechanical Tunability via Hydrogen Bonding in Metal-Organic Frameworks with the Perovskite Architecture

Two analogous metal-organic frameworks (MOFs) with the perovskite architecture, [C(NH2)3][Mn(HCOO)3] (1) and [(CH2)3NH2][Mn(HCOO)3] (2), exhibit significantly different mechanical properties. The marked difference is attributed to their distinct modes of hydrogen bonding between the A-site amine cation and the anionic framework. The stronger cross-linking hydrogen bonding in 1 gives rise to Youngs moduli and hardnesses that are up to twice those in 2, while the thermal expansion is substantially smaller. This study presents clear evidence that the mechanical properties of MOF materials can be substantially tuned via hydrogen-bonding interactions.

Mechanism for linear and nonlinear optical effects in monoclinic bismuth borate (BiB3O6) crystal

Electronic structure calculations of BiB3O6 crystal from first principles are performed based on a plane-wave pseudopotential method. The linear refractive indices and the static second-harmonic generation (SHG) coefficients are also calculated by the SHG formula improved by our group. The calculated values are in good agreement with the experimental values. A real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic groups to the optical response. The results show that the contribution of the (BiO4)5− anionic group to the SHG coefficients is more pronounced than that of the (BO3)3− and (BO4)5− groups.

Deep-ultraviolet transparent phosphates RbBa2(PO3)5 and Rb2Ba3(P2O7)2 show nonlinear optical activity from condensation of [PO4](3-) units.

It is challenging to explore deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials that can achieve a subtle balance between deep-UV transparency and high NLO activity. Known deep-UV NLO materials are almost exclusively limited to borates, except few newly discovered phosphates despite their small NLO activities. Here we report two asymmetric phosphates, RbBa2(PO3)5 (I) and Rb2Ba3(P2O7)2 (II), which feature [PO3]∞ chains and [P2O7](4-) dimers formed by condensation of [PO4](3-) units, respectively. Remarkably, I achieves the desired balance, with the shortest deep-UV absorption edge at 163 nm and the largest NLO activity of 1.4 × KDP (KH2PO4) in deep-UV NLO phosphates. According to first-principles calculations, the enhanced macroscopic SHG response of I can be attributed to the [PO3]∞ chains which exhibit significantly larger microscopic SHG coefficients as compared with the [P2O7](4-) dimers.