Achieving strong optical nonlinearity and wide bandgap of pnictides via ionic motif-driven directed assembly of covalent groups.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39536113.
- Also identified by DOI 10.1126/sciadv.adr2389 and PMC identifier 11559624.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
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: [Sr<sub>4</sub>Br]<sub>2</sub>[M<sup>II</sup><sub>3</sub>Si<sub>25</sub>P<sub>40</sub>] (M<sup>II</sup> = Mg, Cd) and [Ba<sub>3</sub>Br][M<sup>III</sup>Si<sub>10</sub>P<sub>16</sub>] (M<sup>III</sup> = Ga, In), which exhibit strong second harmonic generation effects (5.2 to 7.5 × AgGaS<sub>2</sub>), 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 (Sr<sub>4</sub>Br) and (Ba<sub>4</sub>Br) 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<sup>II/III</sup>P<sub>4</sub> 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.