From KBa ₄ Ge ₃ S ₁₀ Cl to ABa ₃ EuGe ₃ S ₁₁ (A = Na, K) Synthesized by Reactive Flux Assisted Metal Oxide-Boron-Chalcogen (MOBQ) Method: Effect of Cation/Anion Cosubstitution on Crystal Structure and Nonlinear Optical Properties

Chalcogenides are promising candidates to solve the scarcity of currently applicable middle nonlinear optical (NLO) crystals. Herein, heterovalent cosubstitution strategy was applied to [KBa 4 Cl][Ge 3 S 10 ] ( 0 ), which resulted in the discovery of new ABa 3 EuGe 3 S 11 (A = Na ( 1 ), K ( 2 )). Both of them were synthesized via the reactive flux assisted metal oxide-boron-chalcogen (RFMOBQ) routine, and crystallize in the chiral P 6 3 space group. Their quasi-3D structures are constructed by EuS 7 monocapped trigonal prisms and Ge 3 S 9 rings when considering the covalence of Eu–S bonds, which are different from the isolated Ge 3 S 9 cluster in 0 . 1 and 2 show strong NLO responses (0.7 and 0.6 × AgGaS 2 @2.1 μ m) and enhanced laser-induced damage thresholds (4.01 and 4.85 × AgGaS 2 @1064 nm). This work provides a referential case for increasing the structural dimension, which can be applied to the exploration of new NLO crystals.