K2Pb3(CO3)3F2 and KCdCO3F: Novel Fluoride Carbonates with Layered and 3D Framework Structures

Na3K6(CO3)3(NO3)2X·6H2O (X = NO3, Cl, Br): Exploring High-Performance UV Birefringent Crystals Induced by Coplanar π-Conjugated CO3 and NO3 Groups

Planar π-conjugated groups, like CO3, NO3, and BO3 triangles, are ideal functional units for designing birefringent materials due to their large optical anisotropy and wide band gap. The key point for designing birefringent crystals is to select appropriate functional building blocks (FBBs) and the proper arrangement mode. It is well known that the substitution strategy has proven to be a promising and accessible approach. In this work, alkali metals were chosen to regulate and control two different π-conjugated groups, CO3 and NO3, to build new compounds with large birefringence. Subsequently, three new compounds, Na3K6(CO3)3(NO3)2X·6H2O (X = NO3, Cl, Br), were successfully synthesized using the hydrothermal method. The aliovalent substitution between the [NO3]- anionic group and halogen anions [Cl]-/[Br]- has been achieved in these compounds. Na3K6(CO3)3(NO3)2X·6H2O feature the well-coplanar CO3 and NO3 groups in their crystal structure. This coplanar arrangement mode may effectively enhance the anisotropic polarizability of Na3K6(CO3)3(NO3)2X·6H2O. And their experimental birefringence can reach 0.094-0.131 at 546 nm. Diffuse reflectance spectra demonstrate that these compounds exhibit short ultraviolet (UV) absorption edges of ∼235 nm. Meanwhile, Na3K6(CO3)3(NO3)2X·6H2O also have an easily grown capacity under facile conditions. This work not only reports three new potential UV birefringent crystals but also provides a strategy to make the π-conjugated MO3 group coplanar.

A Cation-Driven Approach toward Deep-Ultraviolet Nonlinear Optical Materials

The design of new materials with special performances is still a great challenge, especially for the deep-ultraviolet nonlinear optical materials in which it is difficult to balance large bandgaps and strong second harmonic generation responses due to their inverse relationship. Cation variation not only influences the whole structure frameworks but also directly participates in the formation of electronic structures, both of which could lead to the uncontrollability of the properties of the designed materials. Here, a novel approach, aiming at purposeful and foreseeable material designs, is proposed to characterize the role of cations. By the verification of several series of borates, the influences of cation variation on property changes are explored systematically. Accordingly, a feasible strategy of designing deep-ultraviolet nonlinear optical materials by substituting barium for lead has been concluded, which could obviously blue-shift the ultraviolet cutoff edge and maintain the relatively strong second harmonic generation response (more than 2 times of KH₂PO₄), achieving the property optimization, and especially works efficiently in fluorooxoborates. The property optimization design strategy and the cation characterization method are not only helpful in exploring nonlinear optical materials but also enlightening in material design and selection.

(R)- and (S)-[C8H10NO3]2[NbOF5]: Noncentrosymmetric niobium oxyfluorides with large optical anisotropy

Huge crystals of noncentrosymmetric (NCS) organic-inorganic hybrid niobium oxyfluorides, (R)-[C8H10NO3]2[NbOF5] [(R)-Nb] and (S)-[C8H10NO3]2[NbOF5] [(S)-Nb], have been easily grown via a slow evaporation method in high yields through the systematic driving...

Two molybdenyl carbonates with different dimensional structures exhibiting huge differences in band gaps

Two molybdenyl carbonates with different dimensional structures exhibit huge differences in band gaps, 0D Cs3MoO4(HCO3) exhibiting a much larger band gap than 1D Cs2MoO3(CO3).

KRE(CO3)2 (RE = Eu, Gd, Tb): new mixed metal carbonates with strong photoluminescence and large birefringence

Three new potassium rare earth carbonates KRE(CO3)2 (RE = Eu, Gd, Tb) with strong photoluminescence and large birefringence were synthesized successfully.

Cd3(IO3)(IO4)F2·0.1CdO: A Nonlinear-Optical Crystal with the Introduction of Fluoride into Iodate Containing Both [IO3]- and [IO4]3- Groups

A new d¹⁰ transition-metal iodate fluoride, namely, Cd₃(IO₃)(IO₄)F₂·0.1CdO, was successfully designed and synthesized via the mid-infrared hydrothermal method. It crystallizes in the polar space group R3m and features the coexistence of the [IO₃]^- and [IO₄]^3- groups. Cd₃(IO₃)(IO₄)F₂·0.1CdO has a strong second-harmonic-generation response of about 3.0 times that of KDP(KH2PO4), large birefringence (0.133 at 546.1 nm), and a wide energy band gap (4.00 eV). In addition, the power laser damage threshold (LDT) measurement indicated that it possesses a high LDT of 84.29 MW/cm², which is about 30 times that of AgGaS₂. These superior properties showed that Cd₃(IO₃)(IO₄)F₂·0.1CdO may be an excellent nonlinear-optical crystal for visible and mid-infrared application.

Ba3 (BO3 )(CO3 )F: The First Borate Carbonate Fluoride Synthesized by the High-Temperature Solution Method

In contrast to the well-investigated halogen-containing borates and carbonates, very few halogen-containing borate carbonate compounds have been reported. Specifically, no example of borate carbonate fluoride has been synthesized successfully until now. Herein, the planar π-conjugated units [BO₃ ]^3- and [CO₃ ]^2- and the F^- ions are introduced simultaneously into one crystal structure resulting in the first borate carbonate fluoride, Ba₃ (BO₃ )(CO₃ )F, by the high-temperature solution method in the atmosphere. Its structure features a hexagonal channel formed by the [BO₃ ]^3- and [CO₃ ]^2- units with the [F₃ Ba₈ ]¹³⁺ trimers filled in the channel. Various characterizations including single crystal- and powder-XRD, EDX, IR, UV-vis-NIR, and TG-DSC, together with the first principles calculation have been carried out to verify the structure and fully understand the structure-property relationships.

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.

LiGeBO4: a nonlinear optical material with a balance between deep-ultraviolet cut-off edge and large SHG response induced by hand-in-hand tetrahedra

LiGeBO₄ is found to be a material that can balance a large band gap (>6.2 eV) and strong SHG coefficient (2 × KDP), which is rarely seen in tetrahedral-based crystals.

Role of spin-orbit interaction on the nonlinear optical response of CsPbCO3F using DFT

We explore the effect of spin-orbit interaction (SOI) on the electronic and optical properties of CsPbCO₃F using the full potential linear augmented plane wave method with the density functional theory (DFT) approach. CsPbCO₃F is known for its high powder second harmonic generation (SHG) coefficient (13.4 times (d₃₆ = 0.39 pm V^-1) that of KH₂PO₄ (KDP)). Calculations are done for many exchange correlation (XC) potentials. After the inclusion of SOI, the calculated Tran-Blaha modified Becke-Johnson (TB-mBJ) band gap of 5.58 eV reduces to 4.45 eV in agreement with the experimental value. This is due to the splitting of Pb p-states. Importantly, the occurrence of a band gap along the H-A direction (indirect) transforms to the H-H (direct) high symmetry points/direction in the first Brillouin zone. We noticed a large anisotropy in the calculated complex dielectric function, absorption, and refractive index spectra. The calculated static birefringence of 0.1049 and 0.1057 (with SOI) is found to be higher than that of the other carbonate fluorides. From the Born effective charge (BEC) analysis we notice that the Cs atom shows a negative contribution to birefringence whereas Pb, C, and F atoms show a positive contribution. In addition, we have also calculated the nonlinear optical χ(-2ω;ω,ω) dispersion of a CsPbCO₃F single crystal. We found that d₁₁ = d₁₂ = 4.35 pm V^-1 at 1064 nm, which is 11.2 times higher than d₃₆ of KDP. The origin of the highly nonlinear optical susceptibility dispersion of CsPbCO₃F is explained. Overall, our results are in agreement with experiments and it is obvious from the present study that CsPbCO₃F is a direct band gap, large second harmonic generation, and good phase matchable NLO crystal in the ultraviolet region.

Crystal growth and optical properties of a UV nonlinear optical material KSrCO3F

Large UV NLO KSrCO₃F crystals were grown by a TSSG method, and their linear and nonlinear optical properties were investigated.

Three new phosphates with isolated P2O7units: noncentrosymmetric Cs2Ba3(P2O7)2and centrosymmetric Cs2BaP2O7and LiCsBaP2O7

Three new phosphates, a noncentrosymmetric (NCS) Cs₂Ba₃(P₂O₇)₂and centrosymmetric (CS) Cs₂BaP₂O₇and LiCsBaP₂O₇, have been synthesized from high-temperature solutions for the first time.

Influence of original and simulated microscopic units on SHG response in semiorganic NLO materials

The SHG effect increase was explored by combining the electronic structure, SHG density, molecular orbital analysis and hyperpolarizability density.