Combining a wide band gap, strong second-harmonic generation (SHG), and good phase matchability into a single structure is an ongoing challenge in the design of nonlinear optical (NLO) materials. Herein, we report the first examples of fluorinated gallium selenites AGa₃F₆(SeO₃)₂ [A = Rb (RGFS), Cs (CGFS)] by introducing fluorinated main-group metal octahedra [GaO₂F₄] into the metal selenite system. The two new compounds are isostructural (noncentrosymmetric space group P6₃mc) and feature interesting hexagonal tungsten oxide (HTO)-type [Ga₃F₆(SeO₃)₂]_∞ layers, with alkali metal cations acting as linkers between these layers while also maintaining charge balance. Photophysical studies demonstrate that RGFS and CGFS exhibit strong phase-matchable SHG responses [5.6 × KH₂PO₄ (RGFS) and 5.4 × KH₂PO₄ (CGFS) at 1064 nm], high laser damage thresholds [39.37 MW/cm² (RGFS), 41.59 MW/cm² (CGFS) at 1064 nm, 10 ns pulses, 1 Hz repetition rate], wide band gaps [3.57 eV (RGFS), 3.65 eV (CGFS), the latter the highest value among polar HTO-type selenites or tellurites], and large birefringences (0.097 and 0.092 at 546 nm for RGFS and CGFS, respectively); the two compounds simultaneously exhibit multiple key NLO parameters for practical applications in the near-ultraviolet and mid-infrared region. The critical role of the [GaO₂F₄]^5– groups in the linear and NLO responses in the two materials has been elucidated by first-principles studies. Our report demonstrates that introducing fluorinated main-group metal octahedra into metal selenite systems can lead to promising multicomponent selenite NLO materials.

中文翻译：

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AGA ₃ ˚F ₆（SEO ₃）₂（A =铷，铯）：相位匹配六方晶氧化钨材料的新型带强二次谐波产生响应

将宽带隙，强大的二次谐波（SHG）和良好的相位匹配性结合到一个结构中是非线性光学（NLO）材料设计中的一个持续挑战。此，我们报告的氟代镓硒酸盐AGA第一实施例₃ ˚F ₆（SEO ₃）₂通过引入氟化主族金属八面体[高[A = RB（RGFS），CS（CGFS）] ₂ ˚F ₄ ]到金属亚硒酸盐体系。这两种新化合物具有同构结构（非中心对称空间群P 6 ₃ mc），并具有令人感兴趣的六方氧化钨（HTO）型[Ga ₃ F ₆（SeO ₃）₂ ] _∞层，其中碱金属阳离子充当这些层之间的连接基，同时还保持电荷平衡。光物理研究表明，RGFS和CGFS在1064 nm处具有很强的相位匹配SHG响应[5.6×KH ₂ PO ₄（RGFS）和5.4×KH ₂ PO ₄（CGFS）]，高激光损伤阈值[39.37 MW / cm ²（ RGFS），41.59 MW / cm ²（CGFS）在1064 nm，10 ns脉冲，1 Hz重复频率下]，宽带隙[3.57 eV（RGFS），3.65 eV（CGFS），后者在极性HTO型亚硒酸盐或亚碲酸盐中是最高值]，并且较大双折射（RGFS和CGFS在546 nm处分别为0.097和0.092）; 这两种化合物同时具有多个关键的NLO参数，可用于近紫外和中红外地区的实际应用。第一性原理已经阐明了[GaO ₂ F ₄ ] ^5–基团在两种材料的线性和NLO反应中的关键作用。我们的报告表明，将氟化主族金属八面体引入金属亚硒酸盐体系中可以产生有前途的多组分亚硒酸盐NLO材料。