Reinforced Nonlinear Optical Performances Induced by P-P Homoatomic Bond in Phosphide SrIn₃Si₄P₁₁

Phosphides exhibit great promise as a nonlinear optical (NLO) material system; however, the challenge of simultaneously achieving robust second-harmonic generation (SHG) response, wide band gap, and large birefringence within a single structure remains daunting. Herein, by leveraging the design concept of "multi-asymmetric-module integration", we have successfully harvested a brand-new non-centrosymmetric phosphide SrIn₃Si₄P₁₁, which showcases the characteristics of a three-dimensional framework constructed by diverse [Si₃P₁₀] and [In₃P₁₀] trimers, as well as P-P homoatomic bonds. The introduction of P-P bond distinguishes SrIn₃Si₄P₁₁ from the kindred SrIn₃Si₄P₉, ultimately resulting in "killing three birds with one stone", including a remarkable 30-fold enhancement in SHG intensity, a 2.5-fold increase in birefringence, as well as a 0.50 eV broadening in band gap compared to SrIn₃Si₄P₉. Theoretically calculated analysis reveals that the π interactions and the significant polarization anisotropy of the P-P bond are critical factors contributing to the enhancement of NLO performances. The present study uncovers the pivotal significance of P-P bond in structural design and NLO properties optimization, and delineates a clear research direction for the extensive advancement of phosphides NLO materials.