Novel antimony phosphates with enlarged birefringence induced by lone pair cations

Phosphates, whose obvious disadvantage is the relatively small birefringence, can be overcome by the introduction of post-transition metal cations containing stereochemically active lone-pair electrons. In this paper, two new compounds were successfully explored in the A-Sb-P-O system, i.e. Cs2Sb3O(PO4)3 (CsSbPO) and (NH4)2Sb4O2(H2O)(PO4)2[PO3(OH)]2 (NH4SbPOH). Transmission spectra show that CsSbPO has a surprising transmission range with a UV cutoff edge of 213 nm. First-principles calculations show that both compounds have a wide band gap (5.02 eV for CsSbPO and 5.30 eV for NH4SbPOH) and enlarged birefringence (Δn = 0.034@1064 nm for CsSbPO and Δn = 0.045@1064 nm for NH4SbPOH). The results of real-space atom-cutting investigations show that the distorted [SbOx] polyhedra originating from the asymmetric lone pair electrons give the main contribution to the total birefringence and overcome the disadvantage of small birefringence of phosphates but maintain wide transition windows.

Cd2(IO3)(PO4) and Cd1.62Mg0.38(IO3)(PO4): metal iodate-phosphates with large SHG responses and wide band gaps

The first NLO-active metal iodate-phosphates, namely, Cd₂(IO₃)(PO₄) and Cd_1.62Mg_0.38(IO₃)(PO₄) (1 and 2), with three types of NLO groups, have been reported. 1 and 2 are isostructural and the structure of 1 features a 3D network formed by the Cd₄(IO₃)_8/4(PO₄)_6/3 groups. 1 and 2 with strong SHG signals of 4 × and 3.5 × KH₂PO₄ are promising SHG materials in the visible region.

Li3[Al(PO4)2(H2O)1.5] and Na[AlP2O7]: from 2D layered polar to 3D centrosymmetric framework structures

Two new aluminophosphates with moderate NLO property or a short UV cut-off edge (∼190 nm) are reported.

Struvite-type AMgPO4·6H2O (A = NH4, K): Two Natural Deep-Ultraviolet Transparent Nonlinear Optical Crystals

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play vital roles in diverse fields. Unfortunately, only the KBe₂BO₃F₂ crystal has found commercial applications so far. Therefore, the discovery of new DUV NLO crystals is still urgent. As we all know, digging into the properties of existing crystals is also an effective way to obtain new NLO crystals. Herein, two natural asymmetric orthophosphates AMgPO₄·6H₂O (A = NH₄, K) are proposed. Although their structures and some properties such as infrared spectra, thermal properties, and dielectric properties have been previously characterized, their NLO properties have not been reported. Thus, in this work, these two natural DUV transparent orthophosphates NH₄MgPO₄·6H₂O (NMP) and KMgPO₄·6H₂O (KMP) were successfully acquired by a simple slow evaporation method. The single-crystal X-ray diffraction data indicate that NMP and KMP are isomorphic and that both belong to the Pmn2₁ space group of the orthorhombic system. Remarkably, NMP and KMP possess short cutoff edges below 190 nm, and their second-harmonic generation (SHG) efficiencies are 0.62 and 0.80 times that of KH₂PO₄(KDP), respectively; furthermore, they can achieve type-I phase matching at 1064 nm.

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.

Highly porous aluminophosphates with unique three dimensional open framework structures from mild hydrothermal syntheses

Three novel highly porous aluminophosphates were synthesized through mild hydrothermal methods. Interestingly, among them, α-NaAlPO₄(OH) is polar and exhibits moderate nonlinear optical properties with a short cutoff edge.

Three non-centrosymmetric bismuth phosphates, Li2ABi(PO4)2 (A = K, Rb, and Cs): effects of cations on the crystal structure and SHG response

We reported the synthesis, structure and nonlinear properties of three phosphates, Li₂ABi(PO₄)₂ (A = K, Rb, and Cs), and the effects of cations on the crystal structure and SHG response.

Ionothermal Synthesis of Metal Chalcogenides M2Ag3Sb3S7 (M = Rb, Cs) Displaying Nonlinear Optical Activity in the Infrared Region

Two interesting non-centrosymmetric metal chalcogenides, Rb₂Ag₃Sb₃S₇ and Cs₂Ag₃Sb₃S₇, were synthesized by an ionothermal approach. Crystals of compounds Rb₂Ag₃Sb₃S₇ and Cs₂Ag₃Sb₃S₇ possess isomorphic configuration, consisting of two-dimensional (2D) anionic networks _∞[Ag₃Sb₃S₇]^2-, which are split by alkali-metal M⁺ cations. The band gaps are 2.11 and 2.02 eV for Rb₂Ag₃Sb₃S₇ and Cs₂Ag₃Sb₃S₇, respectively. Second-harmonic generation (SHG) studies revealed that Rb₂Ag₃Sb₃S₇ affords a powder SHG performance of ∼0.5 × AgGaS₂ with type-I phase matching, while Cs₂Ag₃Sb₃S₇ shows a slightly stronger SHG performance of ∼0.6 × AgGaS₂ with type-I phase matching. Both compounds possess broad transparency ranges (∼0.6-20 μm), suggesting their potential as infrared (IR) nonlinear optical (NLO) materials. The laser damage thresholds (LDTs) of both Rb₂Ag₃Sb₃S₇ and Cs₂Ag₃Sb₃S₇ are about 2.3 × AgGaS₂. The calculated birefringence indexes Δn are 0.1885 and 0.1944 at 1.064 μm, respectively, which are sufficiently large enough to achieve phase matching. Theoretical studies using density functional theory have been implemented to further understand the relationship between their NLO properties and band structures.

An alkali metal phosphate RbPbBi2(PO4)3 with three kinds of disorder: the effect of isolated soft cation units on the crystal structure

We have reported a new phosphate, RbPbBi₂(PO₄)₃ with three kinds of disorder, and a concept of isolated soft units has been firstly put forward to study the origin of structural distortions and disorder.

Modulation of perovskite-related frameworks induced by alkaline earth metals in phosphate fluorides A2MPO4F (A = K, Rb; M = Ba, Ca)

A₂CaPO₄F (A = K, Rb) are isomorphs. The 1D zig-zag [FA₄Ca₂]_∞ chains in the two compounds belong to the 1D perovskite-related structure.

Ba3Ca4(BO3)3(SiO4)Cl: a new non-centrosymmetric complex alkaline-earth metal borosilicate chloride with a deep-ultraviolet cut-off edge

The first complex alkaline-earth metal borosilicate chloride, Ba₃Ca₄(BO₃)₃(SiO₄)Cl, as a potential ultraviolet nonlinear optical material.