Jun-Ling Song

Facile Syntheses of Ba2[B4O7(OH)2] and Na[B5O7(OH)2](H2O) Borate Salts Exhibiting Nonlinear Optical Activity in the Ultraviolet

Two novel noncentrosymmetric metal borates, Ba2[B4O7(OH)2] (1) and Na[B5O7(OH)2](H2O) (2), have been obtained by hydrothermal and surfactant-thermal means. Compound 1 consists of novel one-dimensional borate chains formed by B3O9 and B3O8 rings, assembled into a three-dimensional (3D) framework by Ba2+ cations. The structure of 2 exhibits double-helical chains constructed from B5O10 primary building units, which are interconnected via Na+ cations and H-bonding interactions to generate a 3D framework. Second-harmonic-generation (SHG) measurements show that 1 shows a phase-matching powder SHG response of ∼2.2 × KH2PO4 (KDP), while 2 exhibits a weak SHG response. The cutoff edges of 1 and 2 are ∼242 and ∼221 nm, respectively, which suggests that they are potential ultraviolet nonlinear optical (NLO) materials. Band structures and NLO properties have also been theoretically studied.

Solvent-controlled syntheses of mixed-alkali-metal borates exhibiting UV nonlinear optical properties

The mixed-alkali-metal borates NaK(B5O8)(OH)·H2O (1), NaK6[(B4O5)(OH)4]3(OH)·C2H5OH (2) and Na0.33K1.67(B4O5)(OH)4·3H2O (3) have been solvothermally synthesized using various polar organic solvents. Compounds 1 and 2 crystallize in the centrosymmetric space groups P and Rc, respectively. The structure of 1 features a 2D-layered framework constructed by [B5O11]7− primary building units in the ab plane, extending to a 3D framework linked by K+ and Na+ cations, while the structure of 2 can be described as isolated [B4O9]6− primary building units connected by H-bonding interactions and K–O and Na–O bonds, forming a 3D supramolecular framework. Compound 3 crystallizes in the acentric space group P2c, and its UV nonlinear optical properties have been investigated for the first time. Second-harmonic generation (SHG) measurements show that 3 is type-I phase-matching, with a moderate SHG response ca. 0.94 times that of KH2PO4. The cut-off edge of 3 is 242 nm, which suggests that 3 is a potential UV NLO material. Density functional theory calculations have been employed on 3 to rationalize its band structure and electron density as well as the density of states.

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

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.