Salt-inclusion sulfides [K4Cl][MII11In9S26] (MII = Zn, Cd) displaying robust nonlinear optical activity

Abstract

Noncentrosymmetric salt-inclusion chalcogenides (SICs) are a burgeoning class of second-order nonlinear optical (NLO) materials distinguished by their exceptional optical properties. These materials often exhibit robust second-harmonic generation (SHG) responses and possess wide band gaps that typically correspond to their impressive laser-induced damage threshold (LIDT). In this study, we present two isostructural salt-inclusion chalcogenides, namely [K₄Cl][Zn₁₁In₉S₂₆] (1) and [K₄Cl][Cd₁₁In₉S₂₆] (2), which consist of highly parallel-oriented host [M^II₁₁In₉S₂₆]³⁻ frameworks, with guest [K₄Cl]³⁺ ions incorporated to enhance structural stability and maintain charge balance. Notably, compounds 1 and 2 exhibit favorable NLO properties, including strong nonphase matching SHG intensities (1.9 and 5.7 × AgGaS₂ for particle sizes of 30–50 μm) under 1910 nm laser irradiation. Furthermore, compounds 1 and 2 demonstrate suitable band gaps (2.48 and 2.61 eV) and exhibit minimal anisotropy in their thermal expansion coefficients (ranging from 0.09 to 1.01), contributing to their significant LIDT (7.0 and 4.6 × AgGaS₂@1064 nm), respectively.