Greatly enhancing birefringence of fluorosilicates through the synergetic effect of functional units

Abstract

Short-wave ultraviolet optical crystals are widely used in various fields. Exploring organic–inorganic hybrid compounds is an effective approach for discovering crystal materials that simultaneously possess large band gaps and birefringence. In this work, two novel organic–inorganic hybrid fluorosilicates, (C₂H₇N₄O)₂SiF₆ and (C₂H₄N₄)₄ZnSiF₆·H₂O, were obtained. (C₂H₇N₄O)₂SiF₆ has the largest band gap among organic–inorganic hybrid fluorosilicates and a unique [(C₂H₇N₄O)₂SiF₆]_∞ layered structure, while (C₂H₄N₄)₄ZnSiF₆·H₂O has the largest birefringence (0.282@0.546 μm) among reported organic–inorganic hybrid fluorosilicates. In addition, we systematically analyzed the structural and optical properties upon transformation from (C₂H₇N₄O)₂SiF₆ to (C₂H₄N₄)₄ZnSiF₆·H₂O.