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

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, 1; Cs, 2). 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.