Alkali metal–alkaline earth metal borate crystal LiBa₃(OH)(B₉O₁₆)[B(OH)₄] as a new deep-UV nonlinear optical material

Abstract

A new noncentrosymmetric alkali metal–alkaline earth metal borate with the formula LiBa₃(OH)(B₉O₁₆)[B(OH)₄] has been synthesized using a convenient hydrothermal method. The structure features a three-dimensional zeolite-like framework and consists of a [B₉O₁₉(OH)]¹²⁻ primary building unit with 6-membered-ring channels along the c-axis. The Ba dications and [B(OH)₄]− anions are encapsulated in the 6-membered-ring channels, while the Li cations are located between two adjacent [B9O19(OH)]¹²⁻ clusters. Second-harmonic generation (SHG) measurements show that LiBa₃(OH)(B₉O₁₆)[B(OH)₄] is type-I phase-matching, with SHG response ca. 1.2 times that of KH₂PO₄. In addition, it exhibits a wide transparency range with a short UV cut-off edge (<200 nm), suggesting that LiBa₃(OH)(B₉O₁₆)[B(OH)₄] is a potential deep-UV nonlinear optical material. Density functional theory calculations were employed to rationalize the band structure and density of states as well as the electron density.