Na4[B6O9 (OH)3](H2O) Cl: A Deep-Ultraviolet Transparent Nonlinear Optical Borate Chloride with {[B6O9 (OH)3]3-}∞ Chains.

Abstract

The development of nonlinear-optical (NLO) crystals with short ultraviolet cutoff edges is significant and challenging. Here, a new sodium borate chloride, Na4[B6O9 (OH)3](H2O) Cl, was successfully obtained by the mild hydrothermal method, which crystallizes in a polar space group Pca21. The structure of the compound is characterized by {[B6O9 (OH)3]3-}∞ chains. Measurements of optical properties indicate the compound exhibits a deep-ultraviolet (DUV) cutoff edge (≤200 nm) and moderate second harmonic generation response (0.4 × KH2PO4). It presents the first DUV hydrous sodium borate chloride NLO crystal and the first sodium borate chloride possessing a one-dimensional B-O anion framework. Probing into the connection of structure and optical properties has been performed based on theoretical calculations. These results are instructive for designing and obtaining new DUV NLO materials.