Syntheses,Structures And Properties Of Mixed Anionic Groups Nonlinear Optical Crystals

Nonlinear optical crystals play a unique and crucial role in laser science and technology.However,rationally designing a high-performance NLO crystal is still a great challenge because an ideal NLO crystal must not only have the noncentrosymmetric structure but also satisfy the fundamental properties.According to the anionic group theory,the SHG responses in the NLO crystals mainly originate from the anionic groups.The combination of different anionic groups is helpful to construct new structural frameworks and obtain NLO crystals with excellent performance.Through experimental exploration,five new mixed anionic groups crystals were designed and synthesized,and their properties were characterized.1.By combining the structure-directing properties of Mo O₄F₂ octahedra in Ba₂(Mo O₃F₂)F₂ with the substitution of IO₃^-for isovalent F^-anions,a new NCS and polar iodate,Ba₂[Mo O₃F(IO₃)](MO₃F₂)has been successfully designed and synthesized.The SHG response of Ba₂[Mo O₃F(IO₃)](Mo O₃F₂)is an order magnitude larger than Ba₂(Mo O₃F₂)F₂,which is mainly attributable to the substitution of IO₃^-for isovalent F^-anions that increaseed the distortion of Mo-based octahedra and the polarization of the structure.The property measurements indicate that Ba₂[Mo O₃F(IO₃)](MO₃F₂)would be a promising visible or Mid-IR NLO crystal.All of these indicate that combining the structure-directing property of oxyfluorides with chemical substitution is an effective strategy for exploring the high-performance NLO crystals.2.Through the combination of the distorted W-based octahedra with iodate,Ba₂[WO₃F(IO₃)](WO₃F₂)has been successfully synthesized,which features the first example of direct W-O-I bond.The SHG response of Ba₂[WO₃F(IO₃)](WO₃F₂)is weaker than Ba₂[Mo O₃F(IO₃)](MO₃F₂),which is mainly caused by the weaker distortion of W-based octahedra.In addition,this crystal exhibits wide transparency region(0.28–10.74?m),and a moderated birefringence of 0.061@532 nm.3.Through the combination of borate with phosphate and a large B/P ratio,a new family of mixed-coordinated borophosphates,K₃B₄PO₁₀ and K₂MB₄PO₁₀(M=Rb/Cs),was successfully synthesized.The property measurements show that K₃B₄PO₁₀ and K₂MB₄PO₁₀(M=Rb/Cs)all melt congruently and possess deep-ultraviolet cut-off edges.We also calculated the birefringence of K₃B₄PO₁₀,and the results reveal that the birefringence of K₃B₄PO₁₀ is about 0.0445@532 nm,which is larger than other anhydrous borophosphates and mainly contributed by the regular arrangement of?-conjugated BO₃ groups.These results show that B-rich borophosphates are promising systems to synthesize materials with relatively large birefringence.