AeMg_6Ga_6S_(16) (Ae = Ca, Sr, Ba): The First Double Alkaline-Earth Metal Chalcogenides with Excellent Performances

摘要

Infrared nonlinear optical (IR NLO) crystals are of quite significance in thedevelopment of laser technology, yet rationally designing new IR NLO crystalthat can satisfy all the property requirements is still a great challenge owingto the incompatibility between large second harmonic generation (SHG)response and wide band gap. Herein, taking AgGaS_2 (AGS) as the templateand using highly electropositive alkaline-earth metal cations substituting Ag~+cations, the first examples of double alkaline-earth (Ae) metal chalcogenide IRNLO crystals, AeMg_6Ga_6S_(16) (Ae = Ca, Sr, Ba), are successfully designed andsynthesized. Structurally, they possess stable Mg/GaS∞ open frameworks,which can accommodate a wide range of cations from the small size of Ca~(2+) tolarge Ba~(2+) cations and all of the resulting compounds melt congruently. Moreimportantly, these materials achieve the optimal balance among the criticalperformance parameters, including the strong SHG response (≈0.7–0.8 × AGS)and wide band gap (Eg = 3.50–3.54 eV). Theoretical calculations and structureanalysis reveal that their superior NLO properties can be attributed to thesynergistic contribution of the polarizable MgS6 and GaS4 groups.