SrCl2·6H2O: An Alkaline-Earth-Metal Chloride Hexahydrate as Deep-Ultraviolet Nonlinear-Optical Crystal with the {[Sr(H2O)6]2+}∞ Cationic Framework.

Abstract

Exploring deep-ultraviolet (DUV) nonlinear-optical (NLO) materials is significant for the conversion of high-frequency laser. Herein, two alkali-earth-metal halide hexahydrates, SrX2·6H2O (X = Cl, Br), were obtained, and the centimeter-sized single crystals of SrCl2·6H2O were grown by a slow evaporation method. Both of them crystallize in the trigonal space group P321, and their crystal structures show {[Sr(H2O)6]2+}∞ cationic chains, with isolated Cl- or Br- anions interspersed between the chains. SrCl2·6H2O exhibits a moderate second-harmonic-generation response (0.4 × KDP) at 1064 nm and can realize phase matching. Importantly, SrCl2·6H2O has a short ultraviolet cutoff edge (<200 nm). Crystal growth, crystal structures, optical performances, and theoretical calculations of the title and related compounds have been discussed in this work. This study enriches the understanding of metal halide hydrates as NLO materials in the DUV region.