The First Examples of Lithium‐Containing Mixed‐Alkali Strontium Borates with Different Dimensional Anionic Architectures and Short Cutoff Edges

Ba4B14O25: A Deep Ultraviolet Transparent Nonlinear Optical Crystal with Strong Second Harmonic Generation Response Achieved by a Boron-Rich Closed-Loop Strategy

Discovering new deep ultraviolet (DUV) nonlinear optical (NLO) materials is the current research hotspot. However, how to perfectly integrate several stringent performances into a crystal is a great challenge because of the natural incompatibility among them, particularly wide band gap and large NLO coefficient. To tackle the challenge, a boron-rich closed-loop strategy is supposed, based on which a new barium borate, Ba4B14O25, is designed and synthesized successfully via the high-temperature solid-state melting method. It features a highly polymeric 3D geometry with the closed-loop anionic framework [B14O25]8- constructed by the fundamental building blocks [B14O33]24-. The high-density π-conjugated [BO3]3- groups and the fully closed-loop B-O-B connections make Ba4B14O25 possess excellent NLO properties, including short UV cutoff edge (<200 nm), large second harmonic generation response (3.0 × KDP) and phase-matching capability, being a promising DUV-transparent NLO candidate material. The work provides a creative design strategy for the exploration of DUV NLO crystals.

Sc2F2(B2O5): a deep ultraviolet scandium borate fluoride exhibiting large birefringence induced by the synergistic effect of B2O5 and ScOnF2 groups

A rare earth borate fluoride, Sc2F2(B2O5), displays a deep ultraviolet cutoff edge (<200 nm) and very large birefringence induced by the synergistic effect of B2O5 and ScOnF2 groups.

Ba2.5Pb1.5B12O22: structural transformation from a centrosymmetric to a noncentrosymmetric space group by introducing Pb into Ba2B6O11

A new congruent-melting lead barium borate, Ba_2.5Pb_1.5B₁₂O₂₂, was synthesized via a high-temperature solid-state reaction under atmospheric pressure. It crystallizes in the noncentrosymmetric space group Cmc2₁ with a unit cell of a = 19.051(8) Å, b = 10.726(3) Å, c = 8.612(3) Å, and Z = 4. It features a new functional building block (FBB), [B₁₂O₂₆]^16-, that is made up of five [B₃O₈]^7- and one [BO₃]^3- connected by sharing vertex O atoms. It is derived by introducing Pb into Ba₂B₆O₁₁, which leads to a structural transformation from a centrosymmetric to a noncentrosymmetric space group. Its second harmonic generation response (SHG) is approximately 0.9 times that of KDP at the fundamental wavelength of 1064 nm and is also phase-matchable. It has a wide transparent region with a UV cutoff edge of about 250 nm according to the reflectance spectra and high thermal stability, which illustrates that it is a potential candidate for ultraviolet nonlinear optical materials.

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.

Al8(BO3)4(B2O5)F8: A F-Containing Aluminum Borate Featuring Two Types of Isolated B-O Groups

Al₈(BO₃)₄(B₂O₅)F₈, as a new aluminum borate fluoride, has been synthesized by the high-temperature reaction with the closed system for the first time. With respect to its structure, the isolated BO₃ and B₂O₅ groups reside in the center and edge of tunnels constructed by the AlO₄F₂ polyhedra. The AlO₄F₂ polyhedra play the vital role on the formation of isolated B-O groups. According to our investigation, Al₈(BO₃)₄(B₂O₅)F₈ is the first case, which features two types of independently isolated B-O groups in the aluminum borate fluorides. Its cutoff edge is up to deep ultraviolet (DUV) range. What is more, the energy dispersive spectroscopy (EDS), infrared (IR) spectrum, and the first-principles calculations of Al₈(BO₃)₄(B₂O₅)F₈ have been performed.

Synthesis, characterization and crystal structure of a new mixed alkali and alkaline-earth metal borate Rb9Ba24(BO3)19

Rb₉Ba₂₄(BO₃)₁₉ features an intricate 3D Ba–O framework with three types of infinite channels where the Rb⁺ cations and isolated BO₃ units are located.

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.

From BaAl2(BO3)2O to SnAl2(BO3)2F2: structure transformation based on ion regulation

Sn atoms reside in each Al–B–O–F channel consisting of Al₈B₈O₃₂F₁₂ cavities, which makes SnAl₂(BO₃)₂F₂ possess a special structure.

Mg(H2O)6B4O5(OH)4(H2O)3: a new hydrated borate with a short DUV cutoff edge

[B₄O₅(OH)₄] groups are linked together by hydrogen bonds forming undulating pseudo layers, leading to a short cutoff edge.