Great enhancement of the second harmonic generation response is achieved in AgHgPS4 by introducing vacancy defects and highly distorted HgS4 tetrahedra using AgGaS2 as the template.

Chalcogenides with diamond-like (DL) structures are a treasury of infrared nonlinear optical (NLO) materials. Here, a ternary Hg-based chalcogenide with a defect DL structure, Hg 3 P 2 S 8 , is synthesized by solid-state reaction. Driven by the highly distorted [HgS 4 ] tetrahedra, this compound displays an interesting structural symmetry degradation from tetragonal to orthorhombic compared with its analogue Zn 3 P 2 S 8 . Meanwhile, the overall performances of Hg 3 P 2 S 8 are quite remarkable, including a very strong phase-matchable secondharmonic generation (SHG) response (4.2 × AgGaS 2 ), large band gap (2.77 eV), wide IR transparent range (0.45−16.7 μm), and high laserinduced damage threshold (4 × AGS). Furthermore, the theoretical analysis and local dipole moment calculations elucidate that the highly distorted [HgS 4 ] tetrahedra contribute a lot to the enhancement of the SHG effect. This discovery will motivate the exploration of other DL Hg-based chalcogenides serving as high-performing mid-IR NLO materials.

Metal chalcogenides play a critical role in the infrared (IR) nonlinear optical (NLO) field. However, Eu-based chalcogenide-type IR NLO materials are still scarce up to now. In this paper, two new quaternary Eu-based chalcogenides, EuHgGeSe4 and EuHgSnS4, containing the “NLO active groups” [HgQ4]6– (Q = S, Se) and [GeSe4]4–/[SnS4]4– were synthesized through traditional high-temperature solid-state reactions. They possess noncentrosymmetric structures, crystallizing in the Ama2 space group, and exhibit strong phase-matchable second-harmonic-generation (SHG) responses (3.1× and 1.77× that of AgGaS2 for EuHgGeSe4 and EuHgSnS4, respectively). Meanwhile, the optical band gaps of EuHgGeSe4 (1.97 eV) and EuHgSnS4 (2.14 eV) were determined from UV–vis–NIR diffuse reflectance spectra. Differential scanning calorimetry (DSC) analyses reveal the congruent-melting behavior of EuHgGeSe4. Furthermore, structural analysis and theoretical calculations verify the critical driving effects of [HgQ4]6– tetrahedra on the strong SHG activity. The overall results demonstrate that EuHgGeSe4 and EuHgSnS4 are potential IR NLO materials.

A series of nonlinear optical (NLO) chalcohalides AXHg3P2S8 (A = Rb, Cs; X = Cl, Br), which contain various Hg‐based building units including mixed‐anion trigonal planar [HgS2X]3− and tetrahedral [HgS3X]5−, are successfully synthesized. These compounds display good water resistance, wide infrared transparent region (0.42–17 µm), high laser‐induced damage thresholds (4.5–6 × AgGaS2), and strong phase‐matchable second harmonic generation (SHG) response close to AgGaS2. The mixed‐anion chalcohalide groups serving as functional building units in NLO materials are studied for the first time and proven to be very effective. This work opens a new avenue for new NLO material design to achieve the balance between strong SHG efficiency and large bandgap.

The continuous exploration of multinary chalcogenide semiconductors has provided a variety of new functional materials. In this paper, four new quaternary chalcogenides AHgPS 4 (A + = Na + , K + , Rb + , Cs + ) have been prepared by solid-state syntheses. These findings complement the lack of research on this quaternary system. Influenced by the size effect of cations and the coordination mode of Hg, the four compounds crystallize in four different space groups [NaHgPS 4 , P4̅ n2; KHgPS 4 , Pnn2; RbHgPS 4 , P2 1 /n; CsHgPS 4 , P2 1 2 1 2 1 ] and show an interesting evolution from a 3D framework structure to a 1D chain structure. Moreover, all of these compounds feature noncentrosymmetric (NCS) structures except for RbHgPS 4 . The materials exhibit wide band gaps of 2.7 eV < E g < 3.0 eV. The NCS-related second-harmonic-generation (SHG) property of NaHgPS 4 and KHgPS 4 was also studied. They display strong powder SHG responses (3.14 × AgGaS 2 for NaHgPS 4 ; 4.15 × AgGaS 2 for KHgPS 4 ), which indicate their intriguing potential as IR nonlinear-optical materials. Moreover, first-principles theoretical calculations were performed to understand the structure−property relationships of these materials.

Noncentrosymmetric (NCS) structure is the precondition for second-order nonlinear optical (NLO) materials. In this work, we present a new strategy for constructing NCS structures, that mixed alkali-metals made a new...

BaMgBO 3 F, [11] etc. What these compounds have in common is that they all contain π-conjugated anionic groups. According to the anionic group theory, the planar triangular (BO 3 ) 3− and six-membered ring (B 3 O 6 ) 3− groups with conjugated π-orbitals are beneficial to produce large second-harmonic generation (SHG) coefficients and birefringence. [12] Therefore, the π-conjugated anionic groups are chosen frequently to design and synthesize NLO materials until now. Apart from mentioned borate crystals, there are many NLO crystal systems containing other π-conjugated groups, such as carbonates, [13] nitrates, [14] and the emerging cyanurates. [15] Among them, carbonates with planar triangular π-conjugated (CO 3 ) 2− groups play an unignorable role in NLO materials because the perfectly organized (CO 3 ) 2− group is beneficial for large SHG polarizability to improve laser conversion efficiency and moderate birefringence to realize phasematching (PM). [16] In recent years, several carbonates have been reported as UV and even deep-UV NLO crystals such as LiNaCO 3 , [17] NaZnCO 3 (OH), [13b] MNCO 3 F (M = Na/K/Rb/Cs; M = Mg/Ca/Sr/Zn/Cd/Ge/Sn/Pb), [18] Na 3 Ln(CO 3 ) 3 (Ln = Y/Gd), [19] Ln 8 O(CO 3 ) 3 (OH) 15 X (Ln = Y/Lu, X = Cl/Br), [20] etc. To date, some strategies have been adopted for carbonate NLO crystals with intriguing properties: [21] 1) Total cation substitution method. A series of MNCO 3 F NLO crystals with order anion arrangements were found by this approach. Interestingly, CsPbCO 3 F, designed by the replacement of K + and Sr 2+ in KSrCO 3 F by Cs + and Pb 2+ , respectively, shows a remarkably strong SHG response of 13.4 × KH 2 PO 4 (KDP), far greater than that of KSrCO 3 F (3.3 × KDP), owing to the p-π interaction between lone pair active Pb 2+ cation and (CO 3 ) 2− anion. [18a,22] 2) Partial cation substitution method. For instance, taking centric Y 2 (CO 3 ) 3 •H 2 O as a maternal compound, acentric (NH 4 ) 2 Ca 2 Y 4 (CO 3 ) 9 •H 2 O was gained via the partial substitution of Y 3+ with Ca 2+ , causing a large SHG effect of 2.1 × KDP. [23] To our best knowledge, the strategy for the design and synthesis of carbonates by partial anion

Metal-organic framework (MOF) nanomaterials are emerging porous coordinative polymers with large surface area and high porosity. Their application scenarios highly depend on adsorption/desorption dynamics of guest molecules in the framework. For representative ZIF-8 with framework flexibility, the study of molecule transportation in the pore channels of ZIF-8 will address the ambiguity of unclear application scenarios. In this study, the integration of lab-on-fiber technology and nanotechnology are demonstrated for real-time monitoring of adsorption/desorption dynamics of heterocyclic volatile compounds (VOCs) with kinetic diameters larger than the window aperture of ZIF-8. The in-line fiber interferometer with cascaded long-period gratings is used to monitor the real-time refractive index change of VOC adsorption/desorption. The structure-effect relationship between guest VOCs and framework flexibility is analyzed. It shows that the adsorption dynamics is highly related to the molecular geometry and kinetic diameter. The framework flexibility results in the trapping of guest VOCs toluene, pyridine, and tetrahydrofuran in the frameworks. The methanol adsorption/desorption is an effective strategy for the fast desorption of trapped residual VOCs in the framework. Finally, we conceptually demonstrated the real-time monitoring of trace toluene enrichment using ZIF-8 for indoor air purification. This study paves the way for the in-depth understanding of framework flexibility for MOF’s application.