Li4 MgGe2 S7 : The First Alkali and Alkaline-Earth Diamond-Like Infrared Nonlinear Optical Material with Exceptional Large Band Gap.

Large band gap and strong nonlinear optical (NLO) effect are two valuable but contradictory parameters, which are difficult to balance in one infrared (IR) NLO material. Herein, the first alkali and alkaline-earth metal diamond-like (DL) IR NLO material Li4 MgGe2 S7 , presenting a honeycomb-like 3D framework constructed by 6-membered LiS4 rings and GeMgS6 zigzag chains, was rationally designed and synthesized. The introduction of rigid alkali metal and alkaline-earth metal LiS4 and MgS4 tetrahedra effectively broadens the band gap of DL compound to 4.12 eV (the largest one in the reported quaternary metal chalcogenides), generating a high laser damage threshold of 7 × AgGaS2 at 1064 nm. Furthermore, Li4 MgGe2 S7 displays a suitable SHG response (0.7 × AgGaS2 ) with a type I phase-matching behavior. The results indicate that Li4 MgGe2 S7 is a promising IR NLO material for the high-power laser application and it provides an insight into the design of new DL compound with outstanding IR NLO performances.

LiBa4Ga5Q12 (Q = S, Se): Noncentrosymmetric Metal Chalcogenides with a Cesium Chloride Topological Structure Displaying a Remarkable Laser Damage Threshold.

The exploration of novel infrared nonlinear optical (IR NLO) materials with large second-harmonic generation (SHG) responses and wide band gaps has become very imperative recently. Herein we reported two noncentrosymmetric compounds, LiBa4Ga5Q12 (Q = S, Se), crystallizing in space group P421c (No. 114), which feature 3D frameworks built by a basic [Ga5Q16]17- windmill cluster and LiQ4 tetrahedra in a cesium chloride topological structure. Both compounds satisfy the desired balance between good SHG responses (∼1.5× that of AgGaS2) and wide band gaps (3.43 and 2.44 eV) with remarkable laser damage thresholds (21× and 6× that of AgGaS2). The theoretical calculations uncover that the [Ga5Q16]17- cluster makes major contributions to the SHG effect in LiBa4Ga5Q12. In addition, the structure-performance relationship among all compounds in the I-II4-III5-VI12 system has been discussed systematically, which indicates that the introduction of the alkali metal lithium in the I site is beneficial for the production of large band gaps. This work will be helpful in exploring novel IR NLO materials with special structures and comprehensive properties in the chalcogenide system.

Enhanced optical anisotropy via dimensional control in alkali-metal chalcogenides.

Crystals with both large birefringence and wide transparent range are suitable for broad applications in the areas of optical communications, the laser industry and modulation of the light polarization requirement. In this work, to assist the design of urgently needed crystals with large birefringence in the infrared (IR) region, typical alkali-metal chalcogenides, KPSe6, Na2Ge2Se5, and Li2In2GeSe6 have been studied. They exhibit a hierarchical characteristic in the calculated birefringence by about 0.21, 0.11, and 0.04, respectively. To explore the origin of the birefringence difference, the polarizability anisotropy and the effect of electron distribution anisotropy are analyzed. The alkali-metal chalcogenides KPSe6, Na2Ge2Se5, and Li2In2GeSe6 feature infinite one-dimensional (1D) chains of [PSe6], 2D anionic framework of [Ge2Se5] layers and 3D [In2GeSe9] networks, respectively. It is found that the anionic group with low-dimensional configuration could enhance polarizability anisotropy and render large birefringence for the macroscopic structure. This provides evidence that a low-dimensionality configuration in the structure would be beneficial for the enhancement of optical anisotropy, which can motivate the exploration and design of novel IR birefringent materials.

Be2CO3F2 Monolayer: A Flexible Ultraviolet Nonlinear Optical Material via Rational Design.

Multifunctional monolayer materials with attractive properties and novel applications are of present research interest. In this contribution, we design a new monolayer Be2CO3F2 (BCF) by taking a KBe2BO3F2 unique crystal that is able to produce a high energetic laser by a direct second harmonic generation method, as a parent. The cohesive energy, positive phonon modes, and elastic constants reveal that the BCF monolayer is dynamically and mechanically stable, and the appropriate cleavage energy predicts the experimental realization possibility. The property investigations demonstrated that the monolayer BCF has the significantly superiority in flexibility over the representative flexible optoelectronic material MoS2 based on the calculation of Young's modulus. Additionally, the monolayer BCF possesses both a large band gap (5.2 eV) and a second harmonic generation response. These results demonstrate that the monolayer BCF may provide better applications as a promising multifunctional material in the flexible nonlinear optical fields. We hope that this research will pave a new way for designing new generation multifunctional devices.

LiBa2MIIIQ4 (MIII = Al, Ga, In; Q = S, Se): A Series of Metal Chalcogenides with a Structural Transition.

A series of metal chalcogenides, LiBa2MIIIQ4 (MIII = Al, Ga, In; Q = S, Se), have been successfully obtained by the sealed-tube method. LiBa2MIIIQ4 undergoes a special structural transformation from the P21/m (LiBa2AlQ4 and LiBa2GaS4) to the P21/n (LiBa2InQ4) space group, which leads to disparities in electronic states, birefringence, and band gaps. Their structures feature the same zigzag [LiMIIIQ4]4- layers consisting of corner-shared LiQ4 and MIIIQ4 tetrahedra. The Ba atoms serve to bridge the [LiMIIIQ4]4- layers. The structural comparisons show that the radii of MIII and the coordination environments of the Ba atoms (BaQ7 vs BaQ8) cooperatively affect the structural transition from simple mirror m to diagonal glide n in LiBa2MIIIQ4. In addition, a statistical analysis uncovers that the MIII/Ba atomic ratio also plays an important role in regulating the structural transition in Ba- and MIII-based chalcogenides.

A review on the recently developed promising infrared nonlinear optical materials.

Infrared (IR) nonlinear optical (NLO) materials are the key devices for generating tunable infrared output between ∼3 and ∼20 µm by laser frequency conversion techniques. Based on the study of structure and properties, chalcogenides, pnictides and oxides, have been demonstrated as the most promising systems for the exploration of new IR NLO materials with excellent optical performances. Over the past decades, many state-of-the-art IR NLO materials have been discovered in these systems. In this work, the synthesis, characterization and performance of the new developed promising IR NLO materials are summarized and analyzed. The typical IR NLO materials with large-size single crystals are selected as the representatives for the detailed discussions. Moreover, the discrepancies in optical properties of single crystal, polycrystalline powders, and the corresponding calculated results are discussed, aiming to provide suggestions for the exploration of next generation IR NLO material in these systems.

Synthesis, characterization and theoretical investigation of a new chalcohalide, Ba4GaS4F3.

A new fluorine-containing chalcohalide, Ba4GaS4F3, has been synthesized by conventional high-temperature solid-state reaction. The compound crystallizes in the centrosymmetric space group I41/a with a = b = 16.628 (5) Å, c = 17.139 (10) Å, Z = 16. Experimental and theoretical results confirm that Ba4GaS4F3 is a direct band gap compound with an experimental band gap of about 3.13 eV, and the band gap is mainly determined by the Ba-5p, F-2p and S-3p orbitals. What's more, different from the many newly discovered chalcohalides in the Ba3AM4Q (A = Ga, In; M = S, Se; Q = Cl, Br, I) family, Ba4GaS4F3 is the first reported compound in the Ba4AM4D3 (A = Ga, In; M = chalcogen; D = halogen) family. The results enrich the structural diversity of metal chalcohalides.

Syntheses, Structures and Properties of Alkali and Alkaline Earth Metal Diamond-Like Compounds Li2MgMSe4 (M = Ge, Sn).

Two new diamond-like (DL) chalcogenides, Li2MgGeSe4 and Li2MgSnSe4, have been successfully synthesized using a conventional high-temperature solid-state method. The two compounds crystallize in the non-centrosymmetric space group Pmn21 with a = 8.402 (14) Å, b = 7.181 (12) Å, c = 6.728 (11) Å, Z = 2 for Li2MgSnSe4, and a = 8.2961 (7) Å, b = 7.0069 (5) Å, c = 6.6116 (6) Å, Z = 2 for Li2MgGeSe4. The calculated results show that the second harmonic generation (SHG) coefficients of Li2MgSnSe4 (d33 = 12.19 pm/v) and Li2MgGeSe4 (d33 = -14.77 pm/v), mainly deriving from the [MSe4] (M = Ge, Sn) tetrahedral units, are close to the one in the benchmark AgGaS2 (d14 = 13.7 pm/V). The calculated band gaps for Li2MgSnSe4 and Li2MgGeSe4 are 2.42 and 2.44 eV, respectively. Moreover, the two compounds are the first series of alkali and alkaline-earth metal DL compounds in the I2-II-IV-VI4 family, enriching the structural diversity of DL compounds.

ABaSbQ3 (A = Li, Na; Q = S, Se): diverse arrangement modes of isolated SbQ3 ligands regulating the magnitudes of birefringences.

A new series of ABaSbQ3 compounds (A = Li, Na; Q = S, Se) featuring isolated SbQ3 ligands with different arrangement modes was synthesized. The structural transformations (monoclinic to orthorhombic) in the known A-MII-Sb-Q3 system showing an intimate relationship with the differences (Δd = LIIM-Q - LA-Q) were systematically investigated for the first time. Remarkably, the diverse arrangement modes of the isolated SbQ3 ligands have also proven effective at regulating the optical anisotropy based on first principles calculation.

Structural modulation induced by MIIIA metals in Ba3MQ4X (M = Al, Ga, In; Q = S, Se; X = Cl, Br): an experimental and computational analysis.

Four new chalcohalides Ba3AlQ4X (Q = S, Se; X = Cl, Br) have been discovered by a conventional high-temperature method. All of them crystallize in the Pnma space group. The structure is composed of zigzag XBa layers and isolated AlQ4 tetrahedra. Detailed structural comparisons show that the cation size of the MIIIA metals and variable coordination modes of the Ba2+ cations cooperatively influence the framework geometries of the title compounds. The first principles method was also used to investigate the electronic structures and optical properties. Their calculated birefringences range from 0.044 to 0.050 @1064 nm. Real space atom cutting analysis shows that the AlS4, GaS4, and InS4 tetrahedra make the main contribution to the birefringence.

NaBaMIIIQ3 (MIII = Al, Ga; Q = S, Se): first quaternary chalcogenides with isolated edge-sharing (MQ6)6- dimers.

In this study, a new series of NaBaMIIIQ3 (MIII = Al, Ga; Q = S, Se) compounds featuring the first discovered isolated edge-shared (MIII2Q6)6- dimers in known quaternary chalcogenides were synthesized. All compounds showed clear optical anisotropy (Δn = 0.04-0.12) mainly derived from the contribution of isolated (MIII2Q6)6- dimers by the real-space atom-cutting method.