Cation Equivalent Multisubstitution Realizing Structure Transformation and Balanced Nonlinear Optical Performance of Quaternary Eu-Based Chalcogenides

Rare-earth (RE) elements play an important role in constructing nonlinear optical (NLO) materials in view of their capability of creating acentric coordination polyhedra with anions. Here, two new RE chalcogenides EuCdSnQ₄ (Q = S (1), Se (2)) were successfully synthesized by the facile metal oxide-boron-chalcogen/reactive flux hybrid solid-state method by taking EuZnGeS₄ (0) as the parent via two-site equivalent cosubstitution. They crystallize with the orthorhombic noncentrosymmetric space group Fdd2, different from the centrosymmetric Fddd structure of 0. The structural evolution from 0 to 1 and 2 is elucidated in detail. The structures of 1 and 2 feature {[CdSnQ₄]^2–}_∞ layers assembled by {[CdSnQ₂]²⁺}_∞ chains and [CdSnQ₂] quadrilaterals. They both show phase matchable NLO responses of 0.6 (1) and 0.8 (2) × AGS. Theoretical calculations and structural analysis indicate that their good NLO performances are mainly contributed by the [EuQ₈] bicapped trigonal prisms. This work enriches the study of RE-based NLO materials.