Rb1.87Cs1.13B8O13(NO3): a new acentric borate-nitrate with two types of three-dimensional interpenetrating lattices

Abstract

Designing ultraviolet (UV) and deep-UV materials remains a great challenge, especially designing those with multiple anions. By incorporating [NO₃] units into borates and using the high-temperature solution method, a new alkali metal borate-nitrate crystallizing in the acentric space group Pca2₁ was designed and synthesized successfully in sealed quartz tubes. This borate-nitrate, having the formula Rb_1.87Cs_1.13B₈O₁₃(NO₃), consists of interpenetrating porous 3D covalent [B₈O₁₃] and ionic [(NO₃)(Rb/Cs)₃] lattices. It shows a short UV cut-off edge of about 228 nm, and a moderate birefringence (0.047@1064 nm) and SHG response (0.3 × KDP). First principles calculations show that B–O units and [NO₃] units make the predominant contribution to the SHG effects.