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Deep‐ultraviolet (DUV) nonlinear optical (NLO) crystals are vital to the development of science and state‐of‐the‐art technologies, but the exploration of these important optoelectronic materials is hindered by the contradiction between NLO effect and energy band gap as well as the sensitivity of DUV phase‐matching to optical birefringence. Here, in order to achieve a well balanced DUV NLO performance, we chose the diamond‐like structure as the prototype template for the material design and synthesized the first DUV NLO hydroxycarbonate crystal, LiZn(OH)CO3. This compound simultaneously has a wide band gap (>6.53 eV), a strong second harmonic generation response (ca. 3.2×KDP), and a large birefringence (0.147 at 1064 nm) with the shortest DUV phase‐matching capability (λPM<190 nm) among all reported NLO carbonates. Moreover, the structure–property relationships in LiZn(OH)CO3 are analyzed by first‐principles calculations. This work presents an effective design strategy to push the NLO performance of hydroxycarbonates into the DUV region. [ABSTRACT FROM AUTHOR]

Deep‐ultraviolet (DUV) nonlinear optical (NLO) crystals are vital to the development of science and state‐of‐the‐art technologies, but the exploration of these important optoelectronic materials is hindered by the contradiction between NLO effect and energy band gap as well as the sensitivity of DUV phase‐matching to optical birefringence. Here, in order to achieve a well balanced DUV NLO performance, we chose the diamond‐like structure as the prototype template for the material design and synthesized the first DUV NLO hydroxycarbonate crystal, LiZn(OH)CO3. This compound simultaneously has a wide band gap (>6.53 eV), a strong second harmonic generation response (ca. 3.2×KDP), and a large birefringence (0.147 at 1064 nm) with the shortest DUV phase‐matching capability (λPM<190 nm) among all reported NLO carbonates. Moreover, the structure–property relationships in LiZn(OH)CO3 are analyzed by first‐principles calculations. This work presents an effective design strategy to push the NLO performance of hydroxycarbonates into the DUV region. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) transparency, second harmonic effect and optical birefringence are three vital but mutually restrictive factors in the application of UV nonlinear optical (NLO) materials. It is difficult for traditional phosphates to achieve a good balance among these factors. In this communication, we propose that the structural evolution of the NLO motif from traditional phosphate to oxythiophosphate would enhance the birefringence and second harmonic generation (SHG) effect while maintaining wide UV transparency, which is confirmed by first‐principles calculations and preliminary experimental measurements. Following this strategy, we predict that, compared with the well‐known NLO phosphate KH2PO4, the oxythiophosphate KH2PO3S exhibits better balance for the UV NLO performance, including wide UV transparency (UV cutoff down to 203 nm), strong SHG effect (ca. 0.9 pm V−1), and large birefringence (ca. 0.1 at 1 μm) with short phase‐matching SHG output wavelength (≈214 nm). [ABSTRACT FROM AUTHOR]

Commercial infrared (IR) nonlinear optical (NLO) materials are mainly from chalcopyrite‐type AMQ2 (A = Ag, Zn, M = Ga, Ge, Q = S, Se, P) crystals such as AgGaS2 (AGS), AgGaSe2 (AGSe), and ZnGeP2 (ZGP), in which the basic NLO‐active groups are MQ4 tetrahedral units. However, the small anisotropic character of them critical for small birefringence hinders the practical applications in the available IR wavelength range. In this study, a novel strategy for modulating birefringence is proposed using a cation regulation‐driven compressed hypertetrahedral layer approach and a family of AAg2MS4 (A = Na, K, Rb; M = P, As) IR NLO crystals are successfully obtained. Remarkably, the title compounds increase the birefringence to 0.12–0.15, about three times larger than that of AGS (0.04), while they can maintain large bandgaps and strong NLO effects. In addition, they exhibit congruent‐melting properties, beneficial for bulk single crystal growth. The work offers a firsthand access for designing and fabricating high‐performance IR NLO materials. [ABSTRACT FROM AUTHOR]

Cristobalite‐type boron phosphate BPO4, an important nonlinear‐optical (NLO) crystal, exhibits nearly the largest bandgap (Eg ≈ 9.3 eV) and a significant second‐harmonic‐generation (SHG) effect (d36 ≈ 0.7 pm V−1) in the deep‐ultraviolet (DUV, < 200 nm) spectral region. However, its conventional tetrahedral framework structure tends to have low structural anisotropy, resulting in a severe deficiency of birefringence (Δn < 0.01), which fails to achieve DUV birefringent phase matching. In this work, the local anisotropy of tetrahedral structures are proposed to enlarge by constructing van der Waals (vdW) anisotropic motifs under synthetic chemical conditions, which can effectively convert unattainable extreme external forces into internal stresses in chemical bond structures. Depending on unique hierarchical vdW assemblies, enormous tetrahedral distortions can be achieved by stable in‐plane or in‐line bond matching between rigid tetrahedral primitives. First‐principles calculations demonstrate that the birefringence of 2D layered and 1D chained BPO4 achieved by vdW engineering are scaled from Δn < 0.01 to 0.07–0.13, with the shortest birefringent phase‐matched wavelengths down to DUV 189–154 nm. The finding is of seminal importance for the design of vdW NLO crystals in structural chemistry and would provide opportunities to explore unique vdW DUV NLO materials under extreme synthetic conditions. [ABSTRACT FROM AUTHOR]