Realizing Phase‐Matching of Nonlinear Optical [ABa <sub>3</sub> Br <sub>2</sub> ][Ga <sub>5</sub> Se <sub>10</sub> ] (A = Cs, Rb, K, Na) Through Large Anisotropic Lattice Distortion
Meng‐Na Jing, Si‐Fan Lu, Xingwei Jiang, Bin‐Wen Liu, Guo‐Cong Guo
Abstract
Abstract Achieving phase‐matching (PM) behavior by enhancing the birefringence of nonlinear optical (NLO) crystals has been a formidable challenge. Herein, salt‐inclusion chalcogenides [ABa 3 Br 2 ][Ga 5 Se 10 ] (A = Cs, 1 ; Rb, 2 ; K, 3 ; Na, 4 ) that crystal in tetragonal system were synthesized and exhibit smaller c / a ratios (where a and c are the lattice constants) when compared with their Cl‐analogues, indicative of an anisotropic lattice distortion. Along the a ‐ and c ‐axes, the refractive indices show a significant divergence, corresponding to the decrease or increase in electron density. Such anisotropic behavior significantly enhances the birefringence of compounds 1 – 4 (0.044–0.066 @546 nm), realizing the transition from non‐PM (Cl‐analogues) to PM (compounds 1 – 4 ) characteristics at near 2.0 um laser. Moreover, compounds 1 – 4 represent a rare class of selenides that combine significant PM second‐harmonic generation responses (>1.0 × AgGaS 2 ) with wide optical band gaps (>3.0 eV). This work achieves the critical transition from non‐PM to PM behavior through significant anisotropic lattice distortion, thereby offering a new avenue for developing NLO materials.