From (NH4)3[Zr(PO4)2F] to (NH4)3[Sn2(PO4)2]Cl: the rational design of a tin-based short-wave ultraviolet phosphate with large optical anisotropy

Abstract

Exploration of ultraviolet phosphates with large optical anisotropy is of great significance to the development of ultraviolet lasers. Nevertheless, featuring a highly-symmetric structural unit of the PO₄ group, ultraviolet phosphates are usually characterized by small optical anisotropies in spite of the discovery of numerous phosphates, highlighting the great challenge in the design and synthesis of benign ultraviolet phosphates. Herein, a new ultraviolet phosphate of (NH₄)₃[Sn₂(PO₄)₂]Cl was rationally obtained by a substitution-oriented design strategy. With the cosubstitution of Zr⁴⁺ and out-of-plane F⁻ of [Zr(PO₄)₂F]³_∞⁻ layers of (NH₄)₃[Zr(PO₄)₂F], (NH₄)₃[Sn₂(PO₄)₂]Cl featuring new layers of [Sn₂(PO₄)₂]²_∞⁻ and out-of-plane Cl⁻ was successfully isolated, indicating the feasibility of substitution for the design of (NH₄)₃[Zr(PO₄)₂F]-type phosphates. In particular, (NH₄)₃[Sn₂(PO₄)₂]Cl exhibits a wide band gap of 4.7 eV and a large birefringence of 0.065 @ 1064 nm, which is favorable to practical applications.