[ABa₂Cl][Ga₄S₈] (A = Rb, Cs): Wide-Spectrum Nonlinear Optical Materials Obtained by Polycation-Substitution-Induced Nonlinear Optical (NLO)-Functional Motif Ordering

Abstract

Noncentrosymmetry (NCS) is a prerequisite for second-order nonlinear optical (NLO) materials. In this work, a new polycation-substitution-induced centrosymmetry (CS)-to-NCS transformation strategy was applied in CS RbGaS₂, affording two novel NCS salt-inclusion chalcogenides: [ABa₂Cl][Ga₄S₈] (A = Rb, <b>1</b>; Cs, <b>2</b>). Remarkably, they exhibit the key merits of both Vis and IR NLO candidates, including strong phase-matchable second harmonic generation intensities (10.4-15.3 × KH₂PO₄ at 1064 nm; 0.9-1.0 × AgGaS₂ at 1910 nm), high laser-induced damage thresholds (11-12 × AgGaS₂), and a wide transparent window. Their prominent NLO performances originate from the orderly packing of T2-supertetrahedral Ga₄S₁₀ motifs resulting from the template effect of acentric polycation [ClA₂Ba₃]⁷⁺. The CS-to-NCS transformation first realized by polycation-substitution-induced NLO-functional motif ordering provides an effective approach for designing new NLO materials.