K2SO4(NH3SO3)2 and Cs2SO4(NH3SO3)3: Two Deep-UV Transparent Sulfamate-Sulfates with Moderate Birefringence

Abstract

In this work, polar tetrahedron [NH3SO3] and non-polar tetrahedron [SO4]2- were combined to synthesize two deep-UV transparent crystals K2SO4(NH3SO3)2 and Cs2SO4(NH3SO3)3 based on solution evaporation method. Due to the presence of two types of tetrahedral groups with wide bandgap and alkali metal cations without d-d or f-f transitions, both crystals exhibit a deep-UV cutoff edge, approximately 190 nm. Significantly, the birefringence of K2SO4(NH3SO3)2 and Cs2SO4(NH3SO3)3 are 0.0123 and 0.0153 @546 nm, respectively, which are remarkably improved compared to many conventional sulfate crystals. In addition, theoretical calculations were performed to analyze the relationships between the structures and optical properties.