Deep-Ultraviolet Nonlinear Optics in a Borate Framework with 21-Ring Channels

A new borate LiBa₃(OH)[B₉O₁₆][B(OH)₄], which combines the uniform porosity of open-frameworks with the extraordinary NLO properties of borates, has been obtained under hydrothermal conditions by using mixed lithium and barium ions as templates. The framework displays an acs-type net with large 21-ring channels. The second harmonic generation (SHG) measurement shows that it is a type I phase-matchable material with a strong SHG signal intensity about 3.1 times that of KDP (KH₂PO₄). UV/Vis–NIR diffuse reflectance analysis indicates that the compound has a wide transparency range with the short-wavelength absorption edge below 200 nm. These characteristics reveal that the compound is a promising deep-UV nonlinear optical material.