Sr2[B5O8(OH)]2·[B(OH)3]·H2O: A Strontium Borate That Shows Deep‐Ultraviolet‐Transparent Nonlinear Optical Properties

A new noncentrosymmetric strontium borate, P1‐Sr2[B5O8(OH)]2·[B(OH)3]·H2O (1), has been synthesized under the hydrothermal condition. The P1‐Sr2[B5O8(OH)]2·[B(OH)3]·H2O shows a layered B‐O network with 9‐ring windows in the ab plane. Sr2+ cations, H3BO3, and H2O molecules are located in the voids of layers and interlayers, respectively. The P1‐Sr2[B5O8(OH)]2·[B(OH)3]·H2O is the first synthetic phase of veatchite, while the other three polymorphs are found in different natural minerals. This strontium borate is a potential deep‐ultraviolet‐transparent nonlinear‐optical (NLO) crystal whose second‐harmonic‐generation (SHG) intensity is 1.7 times that of KH2PO4 (KDP) and is phase‐matchable. The short wavelength cutoff edge of compound 1 is below 190 nm. Density functional theory (DFT) calculations show that the B–O units are responsible for the nonlinear optical property.