| Second-order nonlinear optical crystals can expand laser wavelength and have significant implications for the development of laser technology.Organic-inorganic hybrid crystal materials have the advantages of both organic and inorganic materials,and are excellent functional materials with important application prospects in the fields of solar cells,sensors,catalysis,photoluminescence,and nonlinear optics.This article explores various organic-inorganic hybrid crystals with second-order nonlinear properties,and investigates their crystal growth,structure,physical properties,and theoretical calculations,obtaining the following research results:Successfully synthesized two kinds of novel lead-free nonlinear optical crystals(C6H10N2)2Bi X7·H2O（X=Cl,Br）with high stability in the corresponding acid solution by using cations with stereochemically active lone pairs of electrons(Bi3+)and 2-aminomethylpyridine（C6H8N2）with planarπ-conjugated structure.Both crystals belong to the orthorhombic crystal system P212121 space group and are zero-dimensional perovskite structure.Their thermal stability,environmental stability and solvent atmosphere stability were studied comprehensively.The relationship between structure and properties was studied by first-principles calculation.The(C6H10N2)2Bi Br7·H2O crystal has a large birefringence of 0.1368 at 1064 nm,which is attributed to the strong anisotropicπ-conjugated electron distribution of the planar 2-aminomethylpyridine.The SHG effect intensity of(C6H10N2)2Bi Cl7·H2O and(C6H10N2)2Bi Br7·H2O are 0.25 and 0.32 times of KDP（KH2PO4）,respectively,and the second-order nonlinear response of the bromide is stronger due to the large distortion of the[Bi Br6]octahedron.This work provides a new idea for exploring low-toxicity and high-stability perovskite structured nonlinear optical materials.By using the organic compound,morpholine（C4H9NO）,containing high electronegative oxygen,combined with chloride and bromide containing the cation(Pb2+)with lone pairs of electrons,two kinds of nonlinear optical crystals(C4H10NO)Pb X3（X=Cl,Br）were synthesized by solvent evaporation.Both crystals belong to the orthogonal P212121 space group of one-dimensional（1D）chain-like perovskite structure.Theoretical calculations showed that the generated second-order nonlinear optical effect was mainly attributed to the distortion of the inorganic octahedral framework[Pb X6].The SHG effect intensities of(C4H10NO)Pb Cl3 and(C4H10NO)Pb Br3 are approximately 0.70 and 0.81 times of KDP,respectively,and the birefringence at 1064 nm are 0.098 and 0.111,respectively,and the laser damage thresholds are 19.94 and 46.82 MW/cm2,respectively.This work provides a new design idea for designing new nonlinear optical crystals by introducing highly electronegative oxygen elements to regulate the crystal symmetry.The lone pair electrons of O in morpholine can be bound to Cd2+through coordination to metal charge transfer strategy,benefiting from the second-order Jahn-Teller effect and the formation of non-centrosymmetric structure by Cd2+cation shift.The introduction of highly electronegative Cl can make the polyhedron of the off-centre crystal more distorted and conducive to strong SHG response.Therefore,by combining the chloride of d10metal cation(Cd2+)and morpholine molecules,the nonlinear optical crystal(C4H10NO)2Cd2Cl6 was synthesized by solvent evaporation.(C4H10NO)2Cd2Cl6belongs to the orthorhombic P212121 space group,with one-dimensional（1D）structures of[Cd Cl6]and[Cd Cl4O2]octahedral distortions.(C4H10NO)2Cd2Cl6 has a short absorption cutoff of 230 nm and SHG response intensity of about 0.73 times of KDP.In addition,related theoretical calculations were carried out to study the relationship between band structure,refractive anisotropy,electronic state and nonlinear optical response.(C4H10NO)2Cd2Cl6 shows good thermal stability.This work realizes the synthesis of organic-inorganic hybrid nonlinear optical crystal with strong SHG response by using d10 transition metal. |
