Achieving strong optical nonlinearity and wide bandgap of pnictides via ionic motif-driven directed assembly of covalent groups

Lihua Gao; Jindong Chen; Xuemei Shi; Yan Xiao; Yinglei Han; Chensheng Lin; Huikang Jiang; Guangsai Yang; Guang Peng; Ning Ye

doi:10.1126/sciadv.adr2389

Achieving strong optical nonlinearity and wide bandgap of pnictides via ionic motif-driven directed assembly of covalent groups

Sci Adv. 2024 Nov 15;10(46):eadr2389. doi: 10.1126/sciadv.adr2389. Epub 2024 Nov 13.

Authors

Lihua Gao¹, Jindong Chen^{1

2}, Xuemei Shi¹, Yan Xiao³, Yinglei Han⁴, Chensheng Lin⁵, Huikang Jiang¹, Guangsai Yang¹, Guang Peng¹, Ning Ye^{1

2}

Affiliations

¹ Tianjin Key Laboratory of Functional Crystal Materials, Institute of Functional Crystal, College of Materials Science and Engineering, Tianjin University of Technology, Tianjin 300384, China.
² Tianjin Key Laboratory of Quantum Optics and Intelligent Photonics, School of Science, Tianjin University of Technology, Tianjin 300384, China.
³ College of Chemistry and Materials Science, Hebei University, Baoding, Hebei 071002, China.
⁴ MOE Key Laboratory of Weak-Light Nonlinear Photonics, School of Physical Sciences, Nankai University, Tianjin 300457, China.
⁵ Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China.

PMID: 39536113
DOI: 10.1126/sciadv.adr2389

Abstract

Noncentrosymmetric (NCS) pnictides are indispensable for nonlinear optics, ferroelectrics, magnetic Weyl electronics, etc., areas, yet their structure design remains a substantial challenge. By using asymmetric ionic unit-driven covalent groups orienting and rigidity-flexibility coupling dual strategy, we successfully design and synthesize four NCS pnictides: [Sr₄Br]₂[M^II₃Si₂₅P₄₀] (M^II = Mg, Cd) and [Ba₃Br][M^IIISi₁₀P₁₆] (M^III = Ga, In), which exhibit strong second harmonic generation effects (5.2 to 7.5 × AgGaS₂), wide bandgaps (1.81 to 1.90 electron volts), and moderate birefringence (0.030 to 0.051). An unprecedented NCS structure-inducing mechanism analysis revealed that the (Sr₄Br) and (Ba₄Br) ionic units featuring the diamond-like electrostatic force field effectively break inversion symmetry and trigger uniform arrangement of the covalent tetrahedron groups. Furthermore, the nonlinear optical (NLO) properties and birefringence can be remarkably tuned by the secondary covalent building blocks (M^II/IIIP₄ tetrahedra) with distinct bond flexibility providing a broader space for regulating the key parameters. This work might expand chemical space for exploiting high-performance pnictide NLO materials.