Assembly of Functional Units for Constructing an Ultraviolet-Transparent Nonlinear Optical Mixed Alkaline Metal Borate-Formate

A new noncentrosymmetric mixed alkaline metal borate-formate, Na2KB6O10(HCOO) (1), has been successfully synthesized under surfactant-thermal conditions. Compound 1 features a three-dimensional B–O framework constructed from [B6O13]8– building units, with two distinct sets of nine-membered-ring channels extending along different crystallographic directions, in which Na+, K+, and HCOO– ions are located for charge balance. It exhibits a broad transparency window in the ultraviolet (UV) region, and its second harmonic generation response is determined to be 1.4 times that of KH2PO4 with phase-matching behavior. This mixed alkaline metal borate-formate is demonstrated to be a promising UV-transparent nonlinear optical crystal.