Photo- and thermoluminescence of BaGa2S4:Eu2+ and BaGa2S4:Eu2+,Ce3+ crystals

Data are presented on the photo- and thermoluminescence of polycrystalline BaGa₂S₄:Eu²⁺ and BaGa₂S₄:Eu²⁺, Ce³⁺ at temperatures from 77 to 300 K. The broad photoluminescence band at 505 nm in BaGa₂S₄:Eu²⁺ is shown to be due to the 4f ⁶5d → 4f ⁷ transition. The broad emission bands at 460 and 510 nm in BaGa₂S₄:Ce³⁺ arise from the 5D (² D _3/2) → 4f ²(² F _5/2) and 5D (² D _3/2) → 4f ²(² F _7/2) transitions. Codoping of BaGa₂S₄ with Eu²⁺ and Ce³⁺ increases the luminescence efficiency owing to energy transfer from Ce³⁺ to Eu²⁺. The thermoluminescence data were used to evaluate the energies of the traps involved: 0.26, 0.31, 0.42, 0.57, and 0.64 eV in BaGa₂S₄:Eu²⁺ and 0.28, 0.32, 0.54, 0.61, and 0.65 eV in BaGa₂S₄:Eu²⁺, Ce³⁺. Original Russian Text ? A.N. Georgobiani, B.G. Tagiev, S.A. Abushov, O.B. Tagiev, Zheng Xu, Suling Zhao, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 151–155.     

Growth and Properties of CdGa2S4 Single Crystals

CdGa₂S₄ single crystals were grown by the Bridgman–Stockbarger method and chemical vapor transport, and their composition, structure, morphology, and transport properties were studied. The crystals were used for the first time to produce In/CdGa₂S₄ surface-barrier structures and H₂O/CdGa₂S₄ photoelectrochemical cells. The photoelectric properties of these devices were investigated in unpolarized and linearly polarized light.     

Photoelectrochemical investigation on spray depositedn-CdIn2S4 thin films

Polycrystalline thin films ofn-CdIn₂S₄ have been spray deposited onto amorphous and fluorinedoped tin oxide (FTO) coated glass substrates at the optimized substrate temperature of 380°C. The films were characterized by X-ray diffraction (XRD) and optical absorption studies. XRD studies revealed that the films were polycrystalline with spinel cubic structure. The optical absorption studies showed the band gap energy to be 2·14 eV. Photoelectrochemical (PEC) investigations were carried out using cell configurationn-CdIn₂S₄/1 M NaOH+1 M Na₂S+1 M S/C. Using Butler model, the optical band gap and minority carrier diffusion length (L _P) were found to be 2·22 eV and 0·07 μm, respectively. Gartner’s model was used to calculate the minority carrier diffusion length and the donor concentration (N _D) for CdIn₂S₄ films at three different wavelengths.N _D was found to be of the order of 10¹⁶ cm⁻³.     

Synthesis and Luminescent Properties of Eu-Activated CaGa2S4 and SrGa2S4

SrS, CaS, SrGa₂S₄:Eu, and CaGa₂S₄:Eu were prepared, and the luminescent properties of the latter two compounds were studied. It is shown that sufficiently pure SrS and CaS powders can be prepared via long-term sulfurization. SrGa₂S₄:Eu and CaGa₂S₄:Eu offer bright green photo-, roentgeno-, and electroluminescence and compare well with commercial analogues.     

[Ba4(S2)][ZnGa4S10]: Design of an Unprecedented Infrared Nonlinear Salt-Inclusion Chalcogenide with Disulfide-Bonds

Salt-inclusion chalcogenides (SICs) have been receiving widespread attention due to their large second harmonic generation (SHG) responses and wide bandgaps, however most of them suffer from small birefringence limiting their technical application. Herein, by introducing the π-conjugated (S₂)²⁻ units in the ionic guest of salt-inclusion structure, the first disulfide-bond-containing SIC, [Ba₄(S₂)][ZnGa₄S₁₀] has been synthesized. It exhibits the widest bandgap up to 3.39 eV among polychalcogenides and strong SHG response as large as that of AgGaS₂ (AGS). Importantly, its birefringence reaches a max value of 0.053@1064 nm among AGS-like SICs, indicating it is a promising IR nonlinear optical (NLO) material. Theoretical calculations reveal that the π-conjugated (S₂)²⁻ units and covalent Ga S layers favor the enhanced birefringence and large SHG response. This work provides not only a new type of SIC for the first time, but also new lights on the design of IR NLO materials.     

System SrGa2S4-LaGaS3

Phase relations in the SrGa₂S₄-LaGaS₃ system were studied by physicochemical analysis, and the SrGa₂S₄-LaGaS₃ phase diagram was mapped out. The system was found to contain the quaternary compound SrLaGa₃S₇, which melts congruently at 1290 K and has a tetragonal structure. The composition ranges of the SrGa₂S₄-and SrLaGa₃S₇-based solid solutions were determined.     

The Thermophysical Properties of Solid Solutions of CaLa2S4-La2S3 System

The thermal conductivity coefficient in the temperature range from 275 to 450 K and the coefficient of thermal expansion in the range from 300 to 900 K are experimentally determined for solid solutions of the CaLa₂S₄-La₂S₃ system. The mechanisms of heat transfer in CaLa₂S₄- La₂S₃ samples in the investigated temperature range are discussed, as well as the factors which define the complex concentration dependence of thermal conductivity coefficient. The correlation is treated between the value and temperature dependence of the coefficient of thermal expansion and the variation of the interatomic bond force in the case of variation of the concentration of cation vacancies in the investigated crystals.     

NiCo2S4 nanoparticles grown on reduced graphene oxides for high-performance asymmetric supercapacitors

The nanostructures of reduced graphene oxide (rGO)/NiCo₂S₄ are prepared using the simple hydrothermal method and the thermal treatment process, which could provide good conductivity and ideal specific surface area. The rGO/NiCo₂S₄ electrode shows a maximum specific capacitance of 1059 F g⁻¹, excellent rate capability, and good cycle life. Furthermore, the three dimensional structures of rGO/MnO (3D rGO/MnO) are also synthesized by the hydrothermal method and the thermal treatment process, which have the high specific surface area and good conductivity. The rGO/MnO electrode exhibits a maximum specific capacitance of 469 F g⁻¹. A rGO/MnO//rGO/NiCo₂S₄ asymmetric supercapacitors (ASC) is assembled using 2 M KOH solution as electrolyte, rGO/NiCo₂S₄ as positive electrode and rGO/MnO as negative electrode. The rGO/MnO//rGO/NiCo₂S₄ ASC shows an energy density of 38.8 Wh kg⁻¹ at a power density of 0.4 kW kg⁻¹ and a good cycle life, which provides a possibility toward actual application in energy-storage systems.     

Z-Scheme Modulated Charge Transfer on InVO4@ZnIn2S4 for Durable Overall Water Splitting

The charge transfer within heterojunction is crucial for the efficiency and stability of photocatalyst for overall water splitting (OWS). Herein, InVO₄ nanosheets have been employed as a support for the lateral epitaxial growth of ZnIn₂S₄ nanosheets to produce hierarchical InVO₄@ZnIn₂S₄ (InVZ) heterojunctions. The distinct branching heterostructure facilitates active site exposure and mass transfer, further boosting the participation of ZnIn₂S₄ and InVO₄ for proton reduction and water oxidation, respectively. The unique Z-scheme modulated charge transfer, visualized by simulation and in situ analysis, has been proved to promote the spatial separation of photoexcited charges and strengthen the anti-photocorrosion capability of InVZ. The optimized InVZ heterojunction presents improved OWS (153.3 µmol h⁻¹ g⁻¹ for H₂ and 76.9 µmol h⁻¹ g⁻¹ for O₂) and competitive H₂ production (21090 µmol h⁻¹ g⁻¹). Even after 20 times (100 h) of cycle experiment, it still holds more than 88% OWS activity and a complete structure.     

Surface Spin Enhanced High Stable NiCo2S4 for Energy-Saving Production of H2 from Water/Methanol Coelectrolysis at High Current Density

Nickel based materials are promising electrocatalysts to produce hydrogen from water in alkaline media. However, the stability is of great challenge, limiting its practical material functions. Herein, a new technique for electro-deposition flower-like NiCo₂S₄ nanosheets on carbon-cloth (CC@NiCo₂S₄) is proposed for energy-saving production of H₂ from water/methanol coelectrolysis at high current density by constructing array architectures and regulating surface magnetism. The optimized and fine-tuned magnetism on the surface of the electrochemical in situ grown CC@NiCo₂S₄ nanosheet array result in (0 1 −1) surface universally exposed, high catalytic activity for methanol electrooxidation, and long-term stability at high current density. X-ray photoelectron spectroscopy in combination of density functional theory calculations confirm the valence electron states and spin of d electrons for the surface of NiCo₂S₄, which enhance the surface stability of catalysts. This technology may be utilized to alter the surface magnetism and increase the stability of Ni-based electrocatalytic materials in general.     

Designing a Transparent CdIn2S4/In2S3 Bulk-Heterojunction Photoanode Integrated with a Perovskite Solar Cell for Unbiased Water Splitting

The integration of photoelectrochemical photoanodes and solar cells to build an unbiased solar-to-hydrogen (STH) conversion system provides a promising way to solve the energy crisis. The key point is to develop highly transparent photoanodes, while its bulk separation efficiency (η_sep.) and surface injection efficiency are as high as possible. To resolve this contradiction, first a novel CdIn₂S₄/In₂S₃ bulk heterojunctions in the interior of nanosheets is designed as a photoanode with high transparency and an ultrahigh η_sep. up to 90%. Furthermore, decorating the ultrathin amorphous SnO₂ layer by atomic layer deposition, the surface oxygen-evolution kinetics of the photoanode are increased significantly. As a result, the onset potential of the photoanode shifts negatively to 0.02 V vs RHE, and the photocurrent density boosts to 2.98 mA cm⁻² at 1.23 V vs RHE, which is ten times higher than that of pristine CdIn₂S₄. Such a high-performance photoanode enables the integrated metal sulfide photoanode–perovskite solar cell system to deliver a STH conversion efficiency of 3.3%.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Geometric isomerism of layered complexes of uranyl selenates: Synthesis and structure of (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)] and (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)](H2O)

New uranyl selenates with organic cations (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)] (I) and (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)](H₂O) (II) were synthesized by evaporation of aqueous solutions and studied. Compound I has monoclinic symmetry, space group C2/c, a = 16.7572(13), b = 11.7239(12), c = 19.0490(13) Å, β = 98.875(6)°, V = 3697.6(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.085 for 2868 reflections with |F _hkl | ≥ 4σ|F _hkl |. Compound II has monoclinic symmetry, space group P2₁/n, a = 10.8252(10), b = 19.0007(10), c = 18.6463(15) Å, β = 100.324(7)°, V = 3773.2(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.084 for 5721 reflections with |F _hkl | ≥ 4σ|F _khl |. The structures of I and II are based on layered complexes [(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)]^3? formed by combination of uranyl pentagonal bipyramids and selenate tetrahedra. H₃O⁺ cations, water molecules, and protonated methylbutylamine cations are located in the interlayer space. Geometric isomerism of two-dimensional complexes [(UO₂)₃(SeO₄)₅(H₂O)] in the structures of uranyl selenates was found and described.     

Spatially Separating Redox Centers on Z‐Scheme ZnIn2S4/BiVO4 Hierarchical Heterostructure for Highly Efficient Photocatalytic Hydrogen Evolution

Photocatalysis technology using solar energy for hydrogen (H₂) production still faces great challenges to design and synthesize highly efficient photocatalysts, which should realize the precise regulation of reactive sites, rapid migration of photoinduced carriers and strong visible light harvest. Here, a facile hierarchical Z‐scheme system with ZnIn₂S₄/BiVO₄ heterojunction is proposed, which can precisely regulate redox centers at the ZnIn₂S₄/BiVO₄ hetero‐interface by accelerating the separation and migration of photoinduced charges, and then enhance the oxidation and reduction ability of holes and electrons, respectively. Therefore, the ZnIn₂S₄/BiVO₄ heterojunction exhibits excellent photocatalytic performance with a much higher H₂‐evolution rate of 5.944 mmol g^?1 h^?1, which is about five times higher than that of pure ZnIn₂S₄. Moreover, this heterojunction shows good stability and recycle ability, providing a promising photocatalyst for efficient H₂ production and a new strategy for the manufacture of remarkable photocatalytic materials.     

A simple chemical route to Bi2S3 hierarchical columniform structures assembled by nanorod-based lamellae

Bi₂S₃ hierarchical columniform structures assembled by nanorod-built lamellae have been first synthesized by a simple wet chemical method through the reaction between Bi(NO₃)₃?5H₂O and CS₂ at 80 °C for 14 h using DMSO as solvent without any surfactants. These new Bi₂S₃ structures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Compared to ethylene glycol and DMF, DMSO supplied an excellent chemical environment favorable to the generation of Bi₂S₃ quickly in heterogeneous condition. The influences of the synthetic parameters were discussed and a possible growth mechanism for the formation of these complex structures was proposed.     

Excellent visible light photocatalytic properties of novel graphene based CdLa2S4/TiO2 heterojunction nanocomposite

This paper introduced one pot method for the synthesis of hybrid CdLa₂S₄-graphene/TiO₂ nanocomposite. The surface properties seen by SEM present a characterization of the texture on CdLa₂S₄-graphene/TiO₂ composites and showed a homogenous composition in the particles. The EDX spectra for the elemental identification showed the presence of C, O and Ti with strong Cd, La and S peaks for the CdLa₂S₄-graphene/TiO₂ nanocomposite. The generation of reactive oxygen species were detected through the oxidation reaction from 1,5-diphenyl carbazide (DPCI) to 1,5-diphenyl carbazone (DPCO). It is found that the photocurrent density and the photocatalytic effect increase in the case with the modified CdLa₂S₄.From the photocatalytic results, the excellent activity of CdLa₂S₄-graphene/TiO₂ nanocompositefor degradation of methylene blue (MB) and Texbrite BA-L (TBA) undervisible irradiation could be attributed to both the effects between photocatalysis of the supported TiO₂ and charge transfer of the grapheme nanosheet, and the introduction of CdLa₂S₄ to enhance the photogenerated electrons.     

Visible light active ZnIn2S4/g-C3N4 heterostructure nanocomposite photoelectrode for efficient photoelectrochemical water splitting activity

Hexagonal zinc indium sulfide coupled g-C₃N₄ (H-ZnIn₂S₄/g-C₃N₄) nanocomposites were synthesized using chemisorption method and its performance towards photoelectrochemical water splitting activity was studied. The H-ZnIn₂S₄/g-C₃N₄ (H-ZIS/CN) nanocomposites exhibited ∼ 1.9 times enhanced photoelectrochemical performance as compared to the H-ZnIn₂S₄. The enhancement in the PEC water splitting activity of H-ZIS/CN nanocomposite is ascribed to the formation of type-II heterojunction which resulted in improved separation of photogenerated charge carriers and faster transfer of charges at the photoelectrode/electrolyte interface. The electrochemical impedance study and Mott-Schottky supported these results. Moreover, during photoelectrochemical reactions, H-ZIS/CN nanocomposites showed tremendous stability under visible light. A potential mechanism of the enhanced photoelectrochemical activity of H-ZIS/CN nanocomposites was proposed and endorsed by the PEC results. This study demonstrates that establishing a heterostructure system by coupling a ternary chalcogenide semiconductor with a conducting polymer is an effective strategy for PEC water splitting applications.     

Structure cristalline du spinelle CdEr2S4

The crystal structure of CdEr₂S₄ is solved from single crystal determinations. The R factor is 0.06 for 120 independent reflections. It is normal spinel, with regular occupancy of the sites. Interatomic distances are : 2.67 Å for ErS, and 2.57 Å for CdS.     

Photoconductivity of MnIn2S4 single crystals

The spectral response of the photocurrent through MnIn₂S₄ single crystals was measured in the temperature range from 77 to 300 K. A considerable photoresponse was detected in the spectral range from 350 to 900 nm. Slow and fast recombination centers were found in the band gap of MnIn₂S₄     

The elastic behaviour of Ce3S4 and La3S4

The hydrostatic pressure and temperature dependences of the elastic stiffnesses of the cubic, Th₃P₄ structure compounds Ce₃S₄ and La₃S₄ have been measured using the ultrasonic pulse echo overlap technique. Although Ce₃S₄, unlike La₃S₄ (T _c = 103 K), does not undergo a phase transition when its temperature is lowered to 16 K, its elastic stiffnesses (C₁₁-C₁₂)/2 and C₁₁ soften with decreasing temperature (in a similar manner but less markedly than those of La₃S₄); this lattice instability indicates an incipient phase transition. In both compounds the elastic constants increase under pressure: the long-wavelength acoustic-mode Grüneisen parameters are all positive, and the application of pressure does not induce acoustic phonon-mode softening.