Noncentrosymmetric Inorganic Open-Framework Chalcohalides with Strong Middle IR SHG and Red Emission: Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb, K)

Novel SHG effective inorganic open-framework chalcohalides, Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb and K), have been synthesized by high temperature solid state reactions. These compounds crystallize in the tetragonal space group <i>I</i>4̅ (No.82) with <i>a</i> = <i>b</i> = 8.7348(6) – 8.6341(7) Å, <i>c</i> = 15.697(3) – 15.644(2) Å, <i>V</i> = 1197.6(3) – 1166.2(2) ų on going from Cs to K. The polar framework of ³_∞[Ga₅Se₁₀]^5– is constructed by nonpolar GaSe₄^5–tetrahedron (T1) and polar supertetrahedral cluster Ga₄Se₁₀^8– (T2) in a zinc-blende topological structure with Ba/A cations and Cl anions residing in the tunnels. Remarkably, Ba₃CsGa₅Se₁₀Cl₂ exhibits the strongest intensity at 2.05 μm (about 100 times that of the benchmark AgGaS₂ in the particle size of 30–46 μm) among chalcogenides, halides, and chalcohalides. Furthermore, these compounds are also the first open-framework compounds with red photoluminescent emissions. The Vienna ab initio theoretical studies analyze electronic structures and linear and nonlinear optical properties

Noncentrosymmetric Inorganic Open-Framework Chalcohalides with Strong Middle IR SHG and Red Emission: Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb, K)

Novel SHG effective inorganic open-framework chalcohalides, Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb and K), have been synthesized by high temperature solid state reactions. These compounds crystallize in the tetragonal space group <i>I</i>4̅ (No.82) with <i>a</i> = <i>b</i> = 8.7348(6) – 8.6341(7) Å, <i>c</i> = 15.697(3) – 15.644(2) Å, <i>V</i> = 1197.6(3) – 1166.2(2) ų on going from Cs to K. The polar framework of ³_∞[Ga₅Se₁₀]^5– is constructed by nonpolar GaSe₄^5–tetrahedron (T1) and polar supertetrahedral cluster Ga₄Se₁₀^8– (T2) in a zinc-blende topological structure with Ba/A cations and Cl anions residing in the tunnels. Remarkably, Ba₃CsGa₅Se₁₀Cl₂ exhibits the strongest intensity at 2.05 μm (about 100 times that of the benchmark AgGaS₂ in the particle size of 30–46 μm) among chalcogenides, halides, and chalcohalides. Furthermore, these compounds are also the first open-framework compounds with red photoluminescent emissions. The Vienna ab initio theoretical studies analyze electronic structures and linear and nonlinear optical properties

Noncentrosymmetric Inorganic Open-Framework Chalcohalides with Strong Middle IR SHG and Red Emission: Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb, K)

Novel SHG effective inorganic open-framework chalcohalides, Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb and K), have been synthesized by high temperature solid state reactions. These compounds crystallize in the tetragonal space group <i>I</i>4̅ (No.82) with <i>a</i> = <i>b</i> = 8.7348(6) – 8.6341(7) Å, <i>c</i> = 15.697(3) – 15.644(2) Å, <i>V</i> = 1197.6(3) – 1166.2(2) ų on going from Cs to K. The polar framework of ³_∞[Ga₅Se₁₀]^5– is constructed by nonpolar GaSe₄^5–tetrahedron (T1) and polar supertetrahedral cluster Ga₄Se₁₀^8– (T2) in a zinc-blende topological structure with Ba/A cations and Cl anions residing in the tunnels. Remarkably, Ba₃CsGa₅Se₁₀Cl₂ exhibits the strongest intensity at 2.05 μm (about 100 times that of the benchmark AgGaS₂ in the particle size of 30–46 μm) among chalcogenides, halides, and chalcohalides. Furthermore, these compounds are also the first open-framework compounds with red photoluminescent emissions. The Vienna ab initio theoretical studies analyze electronic structures and linear and nonlinear optical properties

SiC₂ Siligraphene and Nanotubes: Novel Donor Materials in Excitonic Solar Cells

In excitonic solar cells (XSC), power conversion efficiency (PCE) depends critically on the interface band alignment between donor and acceptor materials. Graphene or silicene is not suitable for donor materials due to their semimetallic features (zero band gaps); it is therefore highly desired to open an energy gap in graphene or silicene to extend their application in optoelectronic devices, especially in photovoltaics. In this paper, based on the global particle-swarm optimization algorithm and the density functional theory methods, we predict a novel SiC₂ siligraphene (g-SiC₂) with a direct band gap of 1.09 eV showing infinite planar geometry, in which Si and C atoms adopt sp² hybridization and C atoms form delocalized 4 C-domains that are periodically separated by Si atoms. Such a g-SiC₂ siligraphene (with a global minimum of energy) is 0.41 eV/atom lower and thermally stabler than the isomeric pt-SiC₂ silagraphene containing planar 4-fold coordinated silicon (3000 K vs 1000 K). Interestingly, the derivative (<i>n</i>, 0), (<i>n</i>, <i>n</i>) nanotubes (with diameters greater than 8.0 Å) have band gaps about 1.09 eV, which are independent of the chirality and diameter. Besides, a series of g-SiC₂/GaN bilayer and g-SiC₂ nanotube/ZnO monolayer XSCs have been proposed, which exhibit considerably high PCEs in the range of 12–20%

First-Principles Study of Lithium Adsorption and Diffusion on Graphene with Point Defects

To understand the effect of point defects on the Li adsorption on graphene, we have studied the adsorption and diffusion of lithium on graphene with divacancy and Stone–Wales defect using the first-principles calculations. Our results show that in the presence of divacancy Li adatom energetically prefers the hollow site above the center of an octagonal ring rather than the top sites of carbon atoms next to vacancy site. In the case of Stone–Wales defect, Li atom is energetically favorable to be adsorbed on the top site of carbon atom in a pentagonal ring shared with two hexagonal rings, and such adsorption results in a bucking of graphene sheet. For divacancy and Stone–Wales defects in graphene, their interactions with a Li adatom are attractive, suggesting that the presence of point defects would enhance the Li adsorption on graphene. The difference charge density and the Bader charge analysis both show that there is a significant charge transfer from Li adatom to it nearest neighbor carbon atoms

Functionalization Based on the Substitutional Flexibility: Strong Middle IR Nonlinear Optical Selenides AX^II₄X^III₅Se₁₂

Seven nonlinear optical (NLO) active selenides in the middle IR region, AX^II₄X^III₅Se₁₂ (A = K⁺–Cs⁺; X^II = Mn²⁺, Cd²⁺; X^III = Ga³⁺, In³⁺) adopting the KCd₄Ga₅S₁₂-type structure, have been synthesized by high-temperature solid-state reaction of an elemental mixture with ACl flux. Their three-dimensional network structures are stacked by M₉Se₂₄-layers of vertex sharing MSe₄ tetrahedra, of which each center is jointly occupied by X^II and X^III atoms. Studies suggest that such tetrahedral building units can be regarded as the “multi-functional sites”, on which the Cd²⁺/Ga³⁺ pair gives rise to the coexistence of NLO and thermochromic properties, and the Mn²⁺/In³⁺ pair leads to the coexistence of NLO and magnetic properties. The density functional theory (DFT) studies and the cutoff-energy-dependent NLO coefficient analyses reveal that such “multi-functional sites” contribute to the origin of the second harmonic generation (SHG) that is ascribed to the electronic transitions from the Se-4p states to the ns, np states of X^II and X^III atoms. Remarkably, title compounds show very strong SHG at an incident wavelength of 2.05 μm, roughly 16–40 times that of commercial AgGaS₂; among them, ACd₄In₅Se₁₂ (A = Rb, Cs) represents the strongest SHG among chalcogenides to date

Functionalization Based on the Substitutional Flexibility: Strong Middle IR Nonlinear Optical Selenides AX^II₄X^III₅Se₁₂

Seven nonlinear optical (NLO) active selenides in the middle IR region, AX^II₄X^III₅Se₁₂ (A = K⁺–Cs⁺; X^II = Mn²⁺, Cd²⁺; X^III = Ga³⁺, In³⁺) adopting the KCd₄Ga₅S₁₂-type structure, have been synthesized by high-temperature solid-state reaction of an elemental mixture with ACl flux. Their three-dimensional network structures are stacked by M₉Se₂₄-layers of vertex sharing MSe₄ tetrahedra, of which each center is jointly occupied by X^II and X^III atoms. Studies suggest that such tetrahedral building units can be regarded as the “multi-functional sites”, on which the Cd²⁺/Ga³⁺ pair gives rise to the coexistence of NLO and thermochromic properties, and the Mn²⁺/In³⁺ pair leads to the coexistence of NLO and magnetic properties. The density functional theory (DFT) studies and the cutoff-energy-dependent NLO coefficient analyses reveal that such “multi-functional sites” contribute to the origin of the second harmonic generation (SHG) that is ascribed to the electronic transitions from the Se-4p states to the ns, np states of X^II and X^III atoms. Remarkably, title compounds show very strong SHG at an incident wavelength of 2.05 μm, roughly 16–40 times that of commercial AgGaS₂; among them, ACd₄In₅Se₁₂ (A = Rb, Cs) represents the strongest SHG among chalcogenides to date

Deep-Ultraviolet Nonlinear Optical Crystals: Ba₃P₃O₁₀X (X = Cl, Br)

Deep-ultraviolet nonlinear optical (deep-UV NLO) crystals are of worldwide interest for the generation of coherent light with wavelength below 200 nm by the direct second-harmonic generation (SHG) output from solid-state lasers. The unprecedented deep-UV NLO phosphates representing their own structure types, Ba₃P₃O₁₀Cl (BPOC), Ba₃P₃O₁₀Br (BPOB), have been discovered, which display moderate powder SHG intensities in type I phase matchable behaviors with a short UV cutoff edge of 180 nm (measured by a single crystal, one of the shortest values among phosphates to date). Insightfully, the geometry and polarization of the <i>C</i>₁-P₃O₁₀^5– building unit are affected by the crystal packing. DFT calculations and cutoff energy dependent SHG coefficient analyses reveal that the SHG origin is from the cooperation of asymmetric <i>C</i>₁-P₃O₁₀^5– anion, Ba²⁺ cation, and Cl^–/Br^– anion

Deep-Ultraviolet Nonlinear Optical Crystals: Ba₃P₃O₁₀X (X = Cl, Br)

Deep-ultraviolet nonlinear optical (deep-UV NLO) crystals are of worldwide interest for the generation of coherent light with wavelength below 200 nm by the direct second-harmonic generation (SHG) output from solid-state lasers. The unprecedented deep-UV NLO phosphates representing their own structure types, Ba₃P₃O₁₀Cl (BPOC), Ba₃P₃O₁₀Br (BPOB), have been discovered, which display moderate powder SHG intensities in type I phase matchable behaviors with a short UV cutoff edge of 180 nm (measured by a single crystal, one of the shortest values among phosphates to date). Insightfully, the geometry and polarization of the <i>C</i>₁-P₃O₁₀^5– building unit are affected by the crystal packing. DFT calculations and cutoff energy dependent SHG coefficient analyses reveal that the SHG origin is from the cooperation of asymmetric <i>C</i>₁-P₃O₁₀^5– anion, Ba²⁺ cation, and Cl^–/Br^– anion

Strong Infrared NLO Tellurides with Multifunction: CsX^II₄In₅Te₁₂ (X^II = Mn, Zn, Cd)

Chalcogenides are the most promising mid- and far-infrared materials for nonlinear optical (NLO) applications. Yet, most of them are sulfides and selenides, and tellurides are still rare. Herein, we report three new KCd₄Ga₅S₁₂-structure type NLO-active tellurides, CsX^II₄In₅Te₁₂ (X^II = Mn, Zn, Cd), synthesized by solid-state reactions. The structure features a 3D diamond-like framework constructed by vertex-sharing asymmetric MTe₄ tetrahedra that are stacked along the <i>c</i>-axis. CsCd₄In₅Te₁₂ exhibits the strongest powder second-harmonic generation (SHG) intensity at 2050 nm (0.61 eV) among tellurides to date, 9 × benchmark AgGaS₂ in the range of 46–74 μm particle size. The primary studies reveal the 1.42 eV direct band gap and high absorption coefficient in the visible spectral region for CsCd₄In₅Te₁₂, suggesting it is a new potential solar cell absorber material. In addition, CsMn₄In₅Te₁₂ also displays a spin-canted antiferromagnetic property below 50 K