Deep-ultraviolet nonlinear optical (DUV NLO) crystals are the key materials to extend the output range of solid-state lasers to below 200 nm. The only practical material KBe BO F suffers high toxicity through beryllium and strong layered growth. Herein, we propose a beryllium-free material design and synthesis strategy for DUV NLO materials. Introducing the (BO F) , (BO F ) , and (BOF ) groups in borates could break through the fixed 3D B-O network that would produce a larger birefringence without layering and simultaneously keep a short cutoff edge down to DUV. The theoretical and experimental studies on a series of fluorooxoborates confirm this strategy. Li B O F is identified as a DUV NLO material with a large second harmonic generation efficiency (0.9×KDP) and a large predicted birefringence (0.07) without layering. This study provides a feasible way to break down the DUV wall for NLO materials.

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More than 3900 crystalline borates, including borate minerals and synthetic inorganic borates, in addition to a wealth of industrially-important boron-containing glasses, have been discovered and characterized. Of these compounds, 99.9 % contain only the traditional triangular BO3 and tetrahedral BO4 units, which polymerize into superstructural motifs. Herein, a mixed metal K5Ba2(B10O17)2(BO2) with linear BO2 structural units was obtained, pushing the boundaries of structural diversity and providing a direct strategy toward the maximum thresholds of birefringence for optical materials design. 11B solid-state nuclear magnetic resonance (NMR) is a ubiquitous tool in the study of glasses and optical materials; here, density functional theory-based NMR crystallography guided the direct characterization of BO2 structural units. The full anisotropic shift and quadrupolar tensors of linear BO2 were extracted from K5Ba2(B10O17)2(BO2) containing BO2, BO3, and BO4 and serve as guides to the identification of this powerful moiety in future and, potentially, previously-characterized borate minerals, ceramics, and glasses.

Deep-ultraviolet nonlinear optical (DUV NLO) crystals are the key materials to extend the output range of solid-state lasers to below200 nm. The only practical material KBe 2 BO 3 F 2 suffers high toxicity through beryllium and strong layered growth. Herein, we propose ab eryllium-free material design and synthesis strategy for DUV NLO materials. Introducing the (BO 3 F) 4À ,( BO 2 F 2 ) 3À ,a nd (BOF 3 ) 2À groups in borates could break through the fixed3DB-O network that would produce al arger birefringence without layering and simultaneously keep as hort cutoff edge down to DUV.T he theoretical and experimental studies on as eries of fluorooxoborates confirm this strategy.L i 2 B 6 O 9 F 2 is identified as aDUV NLO material with alarge second harmonic generation efficiency (0.9 KDP) and al arge predicted birefringence (0.07) without layering.T his study provides af easible way to break down the DUV wall for NLO materials.

Deep-ultraviolet (DUV) nonlinear optical (NLO) crystals that can extend the output range of coherent light below 200 nm are pivotal materials for solid-state lasers. To date, KBe2BO3F2 (KBBF) is the only usable crystal that can generate DUV coherent light by the direct second harmonic generation (SHG), but the layered growth habit and toxic ingredients limit its application. Herein, we report a new fluoroborophosphate (NH4)3B11PO19F3 (ABPF) containing four different functional units-[BO3], [BO4], [BO3F] and [PO4]. ABPF exhibits a KBBF-like structure while eliminating the limitations of KBBF crystal. The unique [B5PO10F]∞ layers help ABPF exhibit excellent performances, such as a large SHG response (1.2 × KDP) and a sufficient birefringence (0.088 at 1064 nm) that enables the shortest phase-matching wavelength (190 nm) to the DUV region. Meanwhile, the introduction of strong B-O-P covalent bonds decreases the layered growth habit. These findings will enrich the structural chemistry of fluoroborophosphate and contribute to the discovery of more excellent DUV NLO crystals.

As important materials in modulating the polarization of light, birefringent crystals have attracted considerable attention and played crucial roles in the field of optical communication and the laser industry. Limited by the transparency range, few birefringent crystals can be used in the deep-ultraviolet (DUV) region, except for α-BaBO (α-BBO). However, the application of α-BBO in the DUV range is restricted by the relatively high cutoff edge and low transmittance rate below 200 nm. In this paper, we design and synthesize a new fluoroborate, NaBOF, by introducing fluorine into borate system. It possesses a short cutoff edge of 169 nm and birefringence larger than 0.080 at 589.3 nm. The NaBOF crystals with sizes up to 3.0 mm × 1.5 mm × 0.2 mm have been grown with good quality by a high-temperature solution method in the open system. First-principles calculations were carried out to understand the optical 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.