Wide band gaps in nonlinear optical materials AMgAgGa6S11 (A = K, Rb) achieved by the incorporation of dual s-block elements in Ag-based sulfide

Abstract

Infrared (IR) nonlinear optical (NLO) material with a concurrently wide band gap and significant NLO coefficient in a single crystal is an incompatible but addressable challenge. Hence, for the first time, the AgGaS2 structure evolved into an Ag-based sulfide system integrating dual s-block elements, guiding the discovery of two NLO crystals named AMgAgGa6S11 (A = K, 1; Rb, 2). Structurally, title phases possess a novel NLO functional motif [AgGa6S17] assembled by two C2-type supertetrahedra through a shared [AgS4] tetrahedron, in which the electropositive cations A+ and Mg2+ are embedded. Thus, compounds 1 and 2 display emulative band gaps (3.15 and 3.25 eV, exceeding that of 2.65 eV in AgGaS2) toward optimizing the laser-induced damage thresholds (3.1 and 3.2 × AgGaS2 @1064 nm). Remarkably, the noncentrosymmetric phases 1 and 2 exhibit moderate second-harmonic generation (SHG) responses (0.6 and 0.7 × AgGaS2 @1910 nm), the greater-than-commercial half of the AgGaS2. To the best of our current knowledge, an experimental birefringence of 1 and 2 (0.029 and 0.027, @546 nm) is first observed in quinary ordered chalcogenides, indicating that samples 1 and 2 meet phase-matching conditions at the incident laser of 1910 nm. All these observations demonstrate that crystals 1 and 2 can become prospective NLO materials. This research will pave the way for discovering excellent IR NLO crystals with wide band gaps and impressive NLO coefficients by incorporating multiple strong electropositive elements into chalcogenides.