Stereochemically active lone-pair-driven giant enhancement of birefringence from three-dimensional CsZn4Ga5Se12 to two-dimensional CsZnAsSe3

Abstract

Birefringent crystals are highly desirable for their important applications in optoelectronic fields. However, the rational design of novel birefringent materials with large birefringence (Δn) has always faced great challenges. In this work, a novel quaternary thioarsenate, CsZnAsSe₃, has been rationally designed and successfully obtained based on a stereochemically active lone pair (SCALP) induction strategy via the facile surfactant–thermal method. In the structure of CsZnAsSe₃, isolated [AsSe₃] triangular pyramids and one-dimensional infinite [Zn–Se]_∞ chains are alternately connected with each other to generate a two-dimensional [ZnAsSe₃]⁻ layer and the charge-balanced Cs⁺ cations are occupied between them. The introduction of SCALP cations not only induces structural dimension transformation but also significantly improves optical anisotropy. Remarkably, CsZnAsSe₃ exhibits a significantly increased Δn (ca. 0.223), which is about 28 times that of the previously reported three-dimensional parent CsZn₄Ga₅Se₁₂ (ca. 0.008). Moreover, detailed theoretical investigation has aided in the deep understanding of the electronic structure and the source of large Δn. This research offers a useful structural design strategy for discovering new chalcogenides with enhanced Δn in the future.