CsSbF2SO4: An Excellent Ultraviolet Nonlinear Optical Sulfate with a KTiOPO4 (KTP)‐type Structure

A novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF₂SO₄, was obtained by ionothermal synthesis. A meticulously designed co‐substitution approach was used to successfully replace the [TiO₆]^8? and [PO₄]^3? functional groups in KTiOPO₄ (KTP) with [SbO₄F₂]^7? and [SO₄]^2? units, respectively. The structure of CsSbF₂SO₄ features a pseudo‐3D framework consisting of interconnected 1D [SbF₂O₂SO₄]^5? chains of corner‐sharing [SbO₄F₂]^7? octahedra and [SO₄]^2? tetrahedra. The title compound exhibits a sharply enlarged band gap compared to its parent compound, KTP, benefitting from the introduction of F^? ions and the displacement of Sb³⁺ cations. Second harmonic generation (SHG) measurements manifested that CsSbF₂SO₄ is phase‐matchable and revealed a strong SHG response of about 3.0 KH₂PO₄ (KDP), which is the highest value reported for any metal sulfate reported to date. The reported fluoride sulfate is a promising near ultraviolet (UV) nonlinear optical (NLO) material.     

Large Second Harmonic Generation (SHG) Effect and High Laser‐Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga₂Se₃ phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS₂ (AGS), respectively. In addition, its IR transparent window ca. 0.59–25 μm is also significantly wider than that of AGS (ca. 0.48–≈11.4 μm). The occurrence of the strong SHG responses and good phase‐matching indicate that the structure of the new Ga₂Se₃ phase can only be non‐centrosymmetric and have a lower symmetry than the cubic γ‐phase. The observed excellent SHG and phase‐matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.     

Prediction of Fluorooxoborates with Colossal Second Harmonic Generation (SHG) Coefficients and Extremely Wide Band Gaps: Towards Modulating Properties by Tuning the BO3/BO3F Ratio in Layers

Fluorooxoborates have inspired investigations of deep‐ultraviolet (DUV) nonlinear optical (NLO) materials that can meet the multiple criteria. Herein, five stable structures with the composition of BaB₂O₃F₂ (I–V) are discovered using the ab initio evolutionary algorithm. Among them, BaB₂O₃F₂‐I has been synthesized experimentally and confirms the reliability of the method. All of the predicted structures possess extremely wide band gaps (8.1–9.0 eV). Moreover, four new structures exhibit giant second harmonic generation (SHG) coefficients (>3×KDP, d₃₆=0.39 pm V^?1). A novel type of the [BOF] layer with BO₃:BO₃F ratio of [1:1] is found in BaB₂O₃F₂‐II and BaB₂O₃F₂‐III. While BaB₂O₃F₂‐IV and BaB₂O₃F₂‐V are solely composed of the BO₃F group and have colossal SHG coefficients (ca. 4×KDP). It gives the direct evidence that the BO₃F group could generate strong SHG effect. Most importantly, the influences of BO₃:BO₃F ratio and their number density on band gap, birefringence and SHG effects are investigated.