RbSe3B2O9(OH) and CsSe3B2O9(OH): one dimensional boroselenite-based anionic frameworks with second harmonic generation properties

M(B(SeO3)3)H2O (M = Al, Ga): the first boroselenites with a unique sandwich like double-layer structure

Exploration of new types of borates is important because of their promising applications in diverse fields. Two new boroselenites, namely, M(B(SeO₃)₃)H₂O (M = Al, Ga), which represent the first IIIA metal boroselenite, were synthesized by hydrothermal reactions. M(B(SeO₃)₃)H₂O (M = Al, Ga) possesses a unique sandwich like double-layer structure formed by two 2D [MSe₂O₈]^5- layers interconnected by 1D [BSeO₅]^3- chains. More interestingly, both compounds display large band gaps (4.86/4.79 eV) and moderate birefringences (Δn = 0.063/0.064 at 1064 nm) based on density functional theory (DFT) calculations.

Bi2[B2(SeO3)6]: A Metal Boroselenite with a Unique Zero-Dimensional [B2(SeO3)6]6- Anionic Group and Large Birefringence

Explorations of new types of borates are important because of their promising application in diverse fields. A new bismuth-containing boroselenite, Bi₂[B₂(SeO₃)₆], has been obtained through high-temperature solid-state reaction in a closed system. Bi₂[B₂(SeO₃)₆] possesses a zero-dimensional [B₂(SeO₃)₆]^6- anionic group that does not belong to any types of reported boroselenites. Besides, Bi₂[B₂(SeO₃)₆] is the first boroselenite with lone-pair electrons containing a metal ion as the countercation. More interestingly, on the basis of the first-principles calculations, this compound displays a large birefringence (0.090) at 1064 nm.

Ba2BS3Cl and Ba5B2S8Cl2: first alkaline-earth metal thioborate halides with [BS3] units

Ba2BS3Cl and Ba5B2S8Cl2 have been synthesized by using PbCl2 as the flux and source of halogen. The two compounds show 3D network structures built by isolated [BS3] units with different Ba-S-Cl groups. This work enriches the structural diversity of boron chemistry and provides an insight into the synthesis of thioborates.

Sr5TeO2(BO3)4 and NaSr5(BO3)(SiO4)2: two inorganic metal borate derivatives with diverse zero dimensional anions

Two new inorganic metal borate derivatives, Sr₅TeO₂(BO₃)₄ and NaSr₅(BO₃)(SiO₄)₂, have been obtained through a high temperature solid reaction method. Sr₅TeO₂(BO₃)₄ crystallizes in a tetragonal space group of P4/mnc featuring a three-dimensional (3D) structure composed of a porous 3D strontium framework stabilized by the unique zero-dimensional (0D) [TeO₂(BO₃)₄]^10- anions. NaSr₅(BO₃)(SiO₄)₂ crystallizes in a monoclinic space group of P2₁/c with a 3D structure consisting of a splendid strontium 3D framework strengthened by isolated BO₃ and SiO₄ groups. The sodium cations located in the empty space of the structure. Thermal stability analyses, optical property measurements and theoretical studies of the compounds were performed. Refractive index calculations revealed that the birefringence of Sr₅TeO₂(BO₃)₄ and NaSr₅(BO₃)(SiO₄)₂ is 0.048 and 0.029, respectively, at 1064 nm.

Effect of anion dimensionality on optical properties: the ∞[B7O10(OH)2] layer in CsB7O10(OH)2vs. the ∞[B7O12] framework in CsBaB7O12

CsB₇O₁₀(OH)₂ with new FBB features a 2D anionic structure whose band gap is about 6.6 eV and CsBaB₇O₁₂ features a 3D anionic structure whose band gap is 5.6 eV. And their simulated birefringence are about 0.08 and 0.05 at 1064 nm, respectively.

Recent progress in selenite and tellurite based SHG materials

Fluorination and bandgaps have attracted more attention than d⁰ TM and SHG efficiency recently in metal selenites and tellurites.

PbCdF(SeO3)(NO3): A Nonlinear Optical Material Produced by Synergistic Effect of Four Functional Units

A new nonlinear optical material, the first fluoride selenite nitrate PbCdF(SeO₃)(NO₃), was successfully synthesized by traditional solid state reactions. This compound crystallizes in the polar space group of Pca2₁, and its structure features a novel 2D layered structure consisting of 1D lead nitrate chains and 2D cadmium selenite layers. PbCdF(SeO₃)(NO₃) exhibits a phase-matchable SHG efficiency of about 2.6 times that of KDP and a wide band gap of 4.42 eV. Its laser damage threshold was measured to be 135.6 MW/cm², which is comparative to that of the reported Li₇(TeO₃)₃F with a short ultraviolet cutoff edge. Theoretical calculation confirmed that the synergistic effects of all the four functional units make PbCdF(SeO₃)(NO₃) a remarkable SHG material.