Influence of Cation on the Anion Frameworks and Properties of Four Lead Phosphates, A2PbBi2(PO4)2(P2O7) (A = Rb, Cs) and A2PbP2O7 (A = K, Rb)

Strategy for a Rational Design of Deep-Ultraviolet Nonlinear Optical Materials from Zeolites

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play a crucial role in cutting-edge laser technology. In order to solve the serious layered growth tendency of the sole commercial DUV NLO crystal KBe2BO3F2 (KBBF), developing alternative systems of compounds with bulk crystal habits has become an urgent task for practical applications. Herein, a novel strategy was developed by applying non-centrosymmetric (NCS) cancrinite (CAN)-type zincophosphates {Na6(OH)2(H2O)2}Cs2[ZnPO4]6 with bulk-crystal habits as the prototype to design new DUV NLO crystals. Two new anhydrous alkali zincophosphates, namely, {(Li6 -xNaxO)A2}[(ZnPO4)6] (A = Cs, Rb; x = 2-3) crystallizing in the NCS hexagonal space group P63 (no. 173) with a CAN-type framework, were successfully synthesized via a modified fluoro-solvo-hydrothermal method by applying triethylamine (TEA) and concentrated NaF solution as a co-solvent. Interestingly, the rigidity of the NCS CAN-type framework acting as the host ensures the non-centrosymmetry of the resulting new compounds. Meanwhile, the replacement of water molecules by guest cationic species in the channels or cages can greatly improve the thermal stability of the resultant crystal and tune its NLO properties. The synergetic effect of the host framework and the guest species makes the two compounds transparent down to the DUV region (<200 nm) and exhibit SHG effects. Therefore, the proposed rational design strategy of applying the known zeotype NCS frameworks as prototypes together with the modified fluoro-solvo-hydrothermal method opens a great avenue for highly effectively exploring new DUV NLO materials.

Phosphates with Two Types of Isolated P-O Groups: Noncentrosymmetric Na6Sr2Bi3(PO4)(P2O7)4 and Centrosymmetric Cs2CaBi2(PO4)2(P2O7)

Inorganic phosphates are of great interest, because of their rich structural chemistry and multiple functional properties. Compared with the phosphates that only contain the solely condensed P-O groups, the phosphates with various condensed P-O groups are less reported, especially for the noncentrosymmetric (NCS) ones. Here, two new bismuth phosphates, Na₆Sr₂Bi₃(PO₄)(P₂O₇)₄ and Cs₂CaBi₂(PO₄)₂(P₂O₇), were synthesized by the solid-state reaction and both structures contain two types of isolated P-O groups. Remarkably, Na₆Sr₂Bi₃(PO₄)(P₂O₇)₄ crystallizes in the tetragonal space group P4̅2₁c, which represents the first NCS bismuth phosphate with PO₄ and P₂O₇ groups. Detailed structural comparisons among Bi³⁺-containing alkali/alkaline-earth metal phosphates show that the ratios of cations/phosphorus profoundly influence the condensed degree of P-O groups. Ultraviolet-visible-near-infrared (UV-vis-NIR) diffusion spectra show that both compounds have the relatively short UV cutoff edges. And Na₆Sr₂Bi₃(PO₄)(P₂O₇)₄ has a second-harmonic generation response of 1.1 × KDP. The first-principles calculations are carried out to understand the structure-performance relationship.

Growth, Structure and Optical Characterization of Rb3Ti3P5O20 Single Crystal

Phosphate crystals attract much attention on account of their rich crystal structures and excellent physical and chemical properties. Herein, Rb3Ti3P5O20 single crystals were grown by the high temperature solution method using Rb2CO3 and NH4H2PO4 as the fluxes. This crystal, with non-centrosymmetric Pca21 space group, presents a three-dimensional framework structure composed of [TiO6] octahedron, [PO4] tetrahedra, and [P2O7] dimers. The electronic structure was measured via X-ray photoelectron spectroscopy. The measurements found that Rb3Ti3P5O20 has stronger Ti–O ionic bonding properties and weaker P–O covalent bonding properties compared to RbTiOPO4. Optical measurements indicated that Rb3Ti3P5O20 has a 3.54 eV band gap and a wide transmission range (0.33–4.5 μm). Theoretical calculations showed that Rb3Ti3P5O20 crystals have a moderate birefringence of 0.079 at 1064 nm. In addition, the relationship of the structure–property was studied using first-principles method. The results demonstrated that TiO6 octahedron played a significant role for the optical properties.

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.

ACs5Bi4(PO4)2(P2O7)3 (A = K, Rb and Cs) with two kinds of isolated P–O groups designed by dimensional reduction theory

ACs5Bi4(PO4)2(P2O7)3 (A = K, Rb and Cs) were successfully designed and synthesized by dimensional reduction theory with a system of A2O–Bi2O3–P2O5.

Syntheses, structures and characterization of non-centrosymmetric Rb2Zn3(P2O7)2 and centrosymmetric Cs2M3(P2O7)2 (M = Zn and Mg)

Three phosphates Rb₂Zn₃(P₂O₇)₂ and Cs₂M₃(P₂O₇)₂ (M = Zn and Mg) were successfully synthesized by a high-temperature solution method.