Ternary AGa5S8 (A = K, Rb, Cs): Promising infrared nonlinear optical materials rationally realized by “one-for-multiple substitution” strategy

Abstract

Commercially available infrared (IR) nonlinear optical (NLO) materials, such as diamond-like AgGaQ2 (Q = S, Se), display large NLO coefficients but relatively low laser-induced damage thresholds (LIDTs), which seriously hinder their widespread laser applications. Herein, the “one-for-multiple substitution” strategy, namely, [SZn46+ + 5Zn2+ ⇒ A+ + 5Ga3+] (A = K, Rb and Cs), is applied on the diamond-like zinc-blende ZnS, and affords three new polar ternary crystals AGa5S8 (A = K, Rb and Cs) through the solid-state method. These compounds inherit the diamond-like anionic backbone framework in ZnS where the NLO functional motifs GaS4 are arranged in a parallel manner. This characteristic accounts for the remarkable phase-matchable second-harmonic generation intensities (1.1–1.2 × AgGaS2). In addition, the inclusion of the highly electropositive A+ cations affords a band gap ranging from 3.10 to 3.37 eV, which facilitates the improvement of LIDT (9.3–12.4 × AgGaS2). To the best our knowledge, crystals AGa5S8 (A = K, Rb and Cs) are the first series of ternary A-inclusion chalcogenides with large second-harmonic generation responses (≥1.0 × AgGaS2) and wide band gaps (≥3.0 eV), fulfilling the rigorous requirements of outstanding IR NLO materials. In addition, the “one-for-multiple substitution” strategy presents the great significance of diamondlike structure evolution and provides a remarkable opportunity to achieve NLO materials. [Figure not available: see fulltext.].