Cd8(BO3)4SiO4: Metal Cation Inducing the Formation of Isolated [BO3] and [SiO4] Units in Borate Silicate

The first compound of cadmium-borate silicate Cd8(BO3)4SiO4, crystallizing in space group P42/n (no. 86), has been successfully synthesized by the conventional high-temperature solution method and melts congruently. The zero-dimensional anionic groups of Cd8(BO3)4SiO4 are isolated [BO3] triangles and isolated [SiO4] tetrahedra which are filled in the framework formed by [CdO6] polyhedra. It has a moderate birefringence (Δn = 0.053 at 546 nm), which is measured by experiment and evaluated by first-principles calculations; meanwhile, the source of birefringence is revealed through the response electronic distribution anisotropy method. The UV-vis-NIR diffuse reflectance spectrum indicates that Cd8(BO3)4SiO4 possesses a wide optical transparency range, with a UV cutoff edge at about 254 nm. This work enriches the structure chemistry of borate silicates, and we discussed the possible methods for the exploration and synthesis of novel optical crystals possessing zero-dimensional anionic groups in the borate silicate system.

A novel broadband Ba3Ca4(BO3)3(SiO4)Cl:Mn4+ near-infrared phosphor with a special pseudo-octahedral Mn4+ coordination structure

A pseudo-octahedral coordination structure of Mn4+ has been innovatively designed, which has realized the maximum red shift and the widest full width at half-maximum (FWHM) of Mn4+ emission so far, not only extending the emission wavelength of Mn4+ to the near-infrared (NIR) region, but also effectively broadening its bandwidth. In the Ba3Ca4(BO3)3(SiO4)Cl:Mn4+ (BCBSC:Mn4+) phosphor, the [Mn/Ca1O9] polyhedron contains one [Mn/Ca1O6] octahedron, which constitutes the pseudo-octahedral coordination structure of Mn4+. The BCBSC:Mn4+ phosphor can be excited at 362 nm and 470 nm and exhibits a broadband NIR emission centered at ∼756 nm with a super-wide range from 650 nm to 1100 nm. The FWHM can reach ∼90 nm. In addition, the internal quantum efficiency (IQE) of the BCBSC:0.01Mn4+ phosphor is 69.7%. The unique luminescence characteristics of BCBSC:Mn4+ phosphors are explored using experimental data and first principles calculation. The significant redshift, the abnormal broadband emission, and the high luminous efficiency are closely related to the special highly distorted [Mn/Ca1O6] pseudo-octahedral coordination environment. The results contribute to comprehending the mechanism of the broadband NIR emission of Mn4+ activated phosphors and broaden the research ideas of developing high-performance Mn4+ doped phosphors for NIR phosphor-converted light-emission diode applications.

Oxychalcogenides as Promising Ultraviolet Nonlinear Optical Candidates: Experimental and Theoretical Studies of AEGeOS2 (AE = Sr and Ba)

Oxychalcogenides have gained widespread attention as promising infrared nonlinear optical (IR-NLO) candidates. However, high-performance oxychalcogenides have rarely been reported in the ultraviolet (UV) region owing to the low energy gaps (E_g < 4.0 eV). Herein, two non-centrosymmetric (NCS) oxychalcogenides with one-dimensional (1D) chain structures and wide E_g (>4.3 eV), namely, AEGeOS₂ (AE = Sr and Ba), have been discovered by combined experiments and theory calculations as a new source of UV-NLO materials. Significantly, they exhibit excellent comprehensive performance comparable to the commercial UV-NLO material KH₂PO₄ (KDP), including large phase-matching ranges (>380 nm), sufficient second harmonic generation intensities (0.7-1.1 × KDP), high laser-induced damage thresholds (1.2 × KDP), wide transparent regions (0.26-12.2 μm), and good thermal stability (up to 1100 K). Moreover, systematic structure-activity relationship analysis illustrates that the 1D homochiral helical [GeOS₂]^2- chains composed of heteroanionic [GeS₂O₂] units make major contribution to the desirable UV-NLO performance. This work makes the two compounds shine out as new energy in the UV-NLO field and offers a new perspective for the exploration of structure-driven functional oxychalcogenides.

NaBa3[M2B7O16(OH)2]F2 (M = Ge, Si): Two Synthetic F Analogues of Garrelsite with [B7O16(OH)2]13- Polyanions and Deep-Ultraviolet Cutoff Edges

Two new borogermanate/borosilicate fluorides, namely, NaBa₃[M₂B₇O₁₆(OH)₂]F₂ (M = Ge, Si), have been successfully synthesized through a conventional mild hydrothermal method. They represent the first examples of mixed alkali and alkaline-earth borogermanate/borosilicate fluorides. NaBa₃[M₂B₇O₁₆(OH)₂]F₂ (M = Ge, Si) crystallize in the space group of C2/c, and their structures feature a unique 3D anionic framework composed of [B₇O₁₆(OH)₂]^13- polyanions corner-sharing with SiO₄ or GeO₄ tetrahedra, forming 1D 10-membered-ring tunnels along the b axis, which are filled by Na⁺, Ba²⁺, and F^- ions. UV-vis-near-IR absorption spectra identify the title compounds possessing short deep-ultraviolet absorption edges (below 200 nm), while their birefringences were calculated to be 0.021 and 0.016 at 1064 nm, respectively. Optical property, thermal stability, and theoretical calculations have also been conducted on NaBa₃[M₂B₇O₁₆(OH)₂]F₂ (M = Ge, Si).

Hexameric poly-fluoroberyllophosphate Na4Be2PO4F5 with moderate birefringence and deep-ultraviolet transmission as a potential zero-order-waveplate crystal

Na4Be2PO4F5 features novel [Be4P2O8F10] hexameric isolated groups, caused due to a cut-off effect from F atoms, and it is an optimal choice to act as a deep-UV zero-order waveplate material.

High-temperature, high-pressure hydrothermal synthesis, crystal structure, and solid state NMR spectroscopy of a lead borosilicate with boron-silicon mixing: Pb6B2Si8O25

A new lead(ii) borosilicate, Pb₆B₂Si₈O₂₅ (1), has been synthesized by a high-temperature, high-pressure hydrothermal reaction at 480 °C and 990 bar. Its structure was determined by single-crystal X-ray diffraction. The reaction product was phase-pure as indicated by powder X-ray diffraction and whole pattern fitting using the Pawley method. Compound 1 has a 2D layer structure with the lead ions being located at interlayer regions. Each layer is formed of corner-sharing BO₄ or SiO₄ tetrahedra and contains an eight-ring window. The layer consists of a new fundamental building block (FBB) with the formula T₈O₂₃ (T: B or Si) formed by two (B(1)_0.8Si(1)_0.2)O₄ tetrahedra and six (Si(2)_0.933B(2)_0.067)O₄ tetrahedra. The FBB can be described as double open-branched triple tetrahedra. Another interesting structural feature of 1 is boron-silicon mixing which is uncommon in borosilicates. There are three unique tetrahedra in the structure: B(1)O₄ tetrahedra with 20% substitution of Si for B, Si(2)O₄ tetrahedra with 6.67% substitution of B for Si, and Si(3)O₄ tetrahedra without substitution. We have applied ¹¹B and ²⁹Si MAS NMR spectroscopy to study the substitutional disorder. The NMR study results not only confirm the mixing of B and Si atoms in the structure, but also verify quantitatively the results from single-crystal X-ray diffraction. The reasons for boron-silicon mixing in the structure are discussed. Crystal data for 1: trigonal, R3[combining macron]c (no. 167), a = 9.5090(2) Å, c = 42.3552(8) Å, V = 3316.7(2) ų, Z = 6, R₁ = 0.0147, and wR₂ = 0.0309.

A new acentric borate-nitrate Cs3B8O13(NO3) with interpenetrating porous 3D covalent and ionic lattices

A new acentric borate-nitrate Cs3B8O13(NO3) was synthesized by a molten salt method which consists of interpenetrating porous 3D covalent [B8O13]∞ and ionic [(NO3)Cs3]∞ lattices. It shows low ultraviolet cut-off edge (202 nm) and phase-matching second harmonic generation (SHG) intensity (0.7 KDP @1064 nm). First principles calculations showed that the main source of SHG is the cooperation of the B-O and [NO3]- groups.

In situ hydrothermal synthesis of polar second-order nonlinear optical selenate Na5(SeO4)(HSeO4)3(H2O)2

An alkali–metal selenate nonlinear optical (NLO) crystal, Na₅(SeO₄)(HSeO₄)₃(H₂O)₂, which possesses good second-order nonlinear optical properties, has been obtained by mild in situ hydrothermal synthesis.

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.

K4(PO2F2)2(S2O7): first fluorooxophosphorsulfate with mixed-anion [S2O7]2- and [PO2F2]- groups

Mixed-anion compounds are among the most promising systems to design functional materials with enhanced properties. Among the phosphate-sulfate species, the [SO4]2- and [PO2F2]- tetrahedra are known and give rise to structural versatility. However, to date, the crystal structures of phosphate-sulfates with the coexistence of two distinct anion groups ([S2O7]2- and [PO2F2]-) in one compound are unknown. Here, a novel type of fluorooxophosphorsulfate, K4(PO2F2)2(S2O7) (KSPOF), is designed and synthesized via a high-temperature method in a closed system. The crystal structure is derived from single-crystal X-ray diffraction (C2/c, a = 13.000(10) Å, b = 7.5430(10) Å, c = 19.010(10) Å, β = 130.070(10)°, and Z = 4). It is the first fluorooxophosphorsulfate with mixed-anion building units ([S2O7]2- and [PO2F2]-) and a unique drum-like cluster was found, which enriches the diversity of structures for fluorooxophosphorsulfate systems. Furthermore, the theoretical calculations indicate that KSPOF possesses moderate birefringence, which mainly originates from the distorted [PO2F2]- tetrahedron.

Full-visible-spectrum lighting realized by a novel Eu2+-doped cyan-emitting borosilicate phosphor

A novel cyan-emitting Ba₃Ca₄(BO₃)₃(SiO₄)Cl:Eu²⁺ inorganic material was developed and its potential application in full-visible-spectrum lighting was explored.