The development of new nonlinear optical (NLO) materials for deep‐ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, ...three new alkali‐metal fluorooxoborates, AB4O6F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH2PO4 (KDP). Interestingly, by judicious selection of the A‐site alkali‐metal cations, the arrangement of NLO‐active structural units is fine‐tuned to an optimal configuration, which contributes to large SHG responses.
Cation control: Three new deep‐ultraviolet nonlinear optical materials with excellent optical properties, comparable to those of KBe2BO3F2, have been obtained by cation‐controlled synthesis.
Conspectus Coherent light radiation down to the deep-ultraviolet spectral range (λ < 200 nm) produced by common laser sources is extensively used in diverse fields ranging from ultrahigh-resolution ...photolithography to photochemical synthesis to high-precision microprocessing. Actually, it is hard to immediately obtain certain wavelengths, deep-ultraviolet coherent light in particular, from commercial laser sources. However, the direct second harmonic generation process governed in part by nonlinear optical crystals is a feasible and effective approach to generate deep-ultraviolet coherent light, which motivates chemists and materials scientists to find potential deep-ultraviolet nonlinear optical materials that can practically meet the scientific requirements. The research progress required to go from a new single-crystal structure to final device applications involves many pivotal steps and is highly time-consuming and challenging, and therefore, it is necessary to commence systematic studies aimed at shortening the research cycle and accelerating the rational design of deep-ultraviolet nonlinear optical materials. In this Account, we choose borates as raw materials because they have ever-greater possibilities to form desired noncentrosymmetric structures, wide optical transparency windows, rich structural chemistry, and also large polarizabilities to guarantee the coexistence of large second-order nonlinear optical coefficients and suitable birefringence. Besides, the effects of fluorine atoms on the structural chemistry and optical properties of borates have been summarized and analyzed. On the basis of these favorable influences, three specific rational design strategies, including experimental and theoretical methods, have been proposed in order to shorten the investigational cycle of discovering the new expected compounds with high physicochemical performances required for practical applications. In this way, the progress of searching for candidates for the next generation of deep-ultraviolet nonlinear optical materials was accelerated from borates to borate fluorides to fluorooxoborates with three effective strategies: (1) expansion of the frontier from borates to borate fluorides with the introduction of fluorine to achieve enhanced optical performance; (2) computer-assisted design of new deep-ultraviolet nonlinear optical materials with a newly introduced systematic global structure optimization method; and (3) expansion of the frontier from borate fluorides to fluorooxoborates by proposed functionalized oxyfluoride BO x F4–x (x+1)– (x = 1, 2, 3) chromophores to balance multiple criteria. The preliminary development of fluorooxoborates exhibiting high performance as a new fertile field to search for deep-ultraviolet nonlinear optical materials is highly encouraging and inspiring and can guide chemists and materials scientists with new directions and thoughts aimed at finding the next generation of practical deep-ultraviolet nonlinear optical materials.
The search of new borates with improved functional properties has attracted considerable attention. Herein, a new polar fluorooxoborate, NaB4O6F (NBF) was prepared by high‐temperature solid‐state ...reaction. NBF belongs to the AB4O6F family (A=alkali metal or ammonium), a series of compounds that undergoes significant cation‐dependent structural changes. NBF is of particular interest owing to the special cation position. Temperature‐dependent ionic conductivity measurements show that NBF is a solid ionic conductor, and it has the lowest active energy of 32.5 kJ mol−1 of fluorooxoborates. NBF also shows a second‐harmonic generation (SHG) response of 0.9×KH2PO4 and 0.2×β‐BaB2O4, at 1064 and 532 nm, respectively, and it has a short UV cutoff edge below 180 nm. Based on bond valence (BV) concepts, symmetry analysis, and the first principles calculation, the unique B4O6F∞ layer can be regarded as the “multifunctional unit”, which is responsible for the observed properties of NBF.
BOF a nova: A new polar fluorooxoborate, NaB4O6F has been discovered through chemical substitution of the cation. It exhibits better ion conductivity than other alkali‐metal fluorooxoborates and excellent NLO properties.
The discovery of new nonlinear optical (NLO) materials for coherent light generation in the deep‐ultraviolet (DUV, wavelength below 200 nm) region is essential for the development of laser ...technologies. Herein, we report a new material CsB4O6F (CBF), which combines the superior structural properties of two well‐known NLO materials, β‐BaB2O4 (BBO) and KBe2BO3F2 (KBBF). CBF exhibits excellent DUV optical properties including a short cutoff edge (155 nm), a large SHG response (≈1.9×KDP), and a suitable birefringence that enables frequency doubling down to 171.6 nm. Remarkably, CBF melts congruently and shows an improved growth habit. In addition, our rational design strategy will contribute to the discovery of DUV NLO materials.
A beryllium‐free deep‐ultraviolet nonlinear optical material, CsB4O6F, combines the superior functional and structural properties of two established NLO materials, β‐BaB2O4 and KBe2BO3F2. CsB4O6F exhibits excellent DUV optical properties, a large SHG response, and a suitable birefringence that enables frequency doubling down to 171.6 nm.
Abstract
Nonlinear optical (NLO) materials are the vital components of future photoelectric technologies as they can broaden the tunable wavelength range supplied by common laser sources. However, ...the necessary prerequisites for a practical NLO material are rather strict. Accordingly, considerable efforts have been focused on finding potential NLO materials. Here we report two asymmetric beryllium-free borates
Pna
2
1
- and
P
$$\bar 6$$
6
̄
2
m
-Ba
3
Mg
3
(BO
3
)
3
F
3
featuring NLO-favorable
2
∞
Mg
3
O
2
F
3
(BO
3
)
2
layered structures. The reversible phase transition among two polymorphs was demonstrated by multiple experimental tests. The optical measurements reveal that
Pna
2
1
-Ba
3
Mg
3
(BO
3
)
3
F
3
possesses the optical properties required for ultraviolet NLO applications. Remarkably,
Pna
2
1
-Ba
3
Mg
3
(BO
3
)
3
F
3
has a large laser damage threshold, a deep-ultraviolet cutoff edge, a favorable anisotropic thermal expansion as well as the capacity of insolubility in water. These optical properties can be comparable or superior to that of commercial NLO material
β
-BaB
2
O
4
, which make
Pna
2
1
-Ba
3
Mg
3
(BO
3
)
3
F
3
a promising ultraviolet NLO material.
Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; ...however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements.
Crack-free and almost fully dense (≥99%) bulk-form titanium matrix nanocomposites in-situ synthesized from a ball-milled mixture of Ti-6Al-4V and B4C powders were achieved through an optimized ...selective laser melting (SLM) process. The effects of minor B4C addition on microstructure evolution, hardness, compressive properties and fracture mechanisms of the composites were systematically investigated. The in-situ synthesized nanoscale TiBw or TiCp ceramic reinforcements, exhibiting a quasi-continuous (TMC1) or full-continuous structure (TMC2), could play a prominent role in determining the microstructure refinement and mechanical properties of the composites. Results indicate that the SLM-processed nanocomposites exhibit a maximum increase of 45% of Vickers microhardness and 26% of ultimate compressive strength over the Ti-64 alloy. The enhancement of mechanical properties is mainly attributed to the second-phase strengthening, grain refinement strengthening as well as solid solution strengthening induced by the interstitial carbon in Ti matrix. This study provides a novel solution for microstructure tailoring with minor B4C addition and producing high-performance titanium matrix composites via SLM additive manufacturing.
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•Crack-free bulk-form titanium matrix nanocomposites with relative density ≥99% were fabricated by selective laser melting.•In-situ synthesized nanoscale TiB whiskers or TiC particles distributed in the titanium matrix were achieved.•The composites evolve from quasi-continuous to full-continuous wall-like or network structure with increasing B4C content.•The composites show a maximum increase of 45% of Vickers microhardness and 26% of compressive strength over the Ti-64.
Elucidating the orbital level origin of second harmonic generation (SHG) in materials and identifying the local contributions is a long-standing challenge. We report a first principles approach for ...the SHG where the contributions from individual orbitals or atoms can be evaluated via symmetry adapted Wannier functions without semiempirical parameters. We apply this method to the common SHG materials KBe2BO3F2, KCaCO3F, and β−BaB2O4, and show that the orbitals on noncentrosymmetric sublattices are responsible for SHG effect and the energies of these orbitals control the magnitude.
Birefringent materials play indispensable roles in modulating the polarization of light and are vital in the laser science and technology. Currently, the design of birefringent materials operating in ...the deep-ultraviolet region (DUV, λ ≤200 nm) is still a great challenge. In this work, we developed a new DUV birefringent crystal LiBO
based on BO
infinite chains in the Li-B-O system, which simultaneously achieves the shortest UV cutoff edge (164 nm) and the largest birefringence (≥0.168 at 266 nm) among all the reported borate-based DUV birefringent materials. Single crystals of LiBO
with dimensions up to Ø55 × 34 mm
were grown by the Czochralski method, providing access to large-sized single crystal with low cost. Moreover, it has a high laser damage threshold and stable physicochemical properties. These outstanding characters unambiguously support that LiBO
can be an excellent birefringent material for DUV application.
In this paper, we propose a blind image watermarking algorithm based on the multiband wavelet transformation and the empirical mode decomposition. Unlike the watermark algorithms based on the ...traditional two-band wavelet transform, where the watermark bits are embedded directly on the wavelet coefficients, in the proposed scheme, we embed the watermark bits in the mean trend of some middle-frequency subimages in the wavelet domain. We further select appropriate dilation factor and filters in the multiband wavelet transform to achieve better performance in terms of perceptually invisibility and the robustness of the watermark. The experimental results show that the proposed blind watermarking scheme is robust against JPEG compression, Gaussian noise, salt and pepper noise, median filtering, and Con-vFilter attacks. The comparison analysis demonstrate that our scheme has better performance than the watermarking schemes reported recently.
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