Formation of Crystalline CdSe Particles from a Single‐Source‐Precursor according to Ostwald's Rule

The formation of crystalline CdSe particles in the thermal degradation of Cd(SePh)₂·TMEDA (TMEDA = tetramethylethylenediamine) as a single‐source‐precursor was investigated by in‐situ powder X‐ray diffraction. It was shown that the primary grains were formed in the cubic zinc blende modification. After an increase in particle size by further annealing a phase transition to the thermodynamically favored hexagonal wurtzite type was detected. This behaviour indicates that, according to Ostwald's rule, the primary grains consist of the less stable polymorph due to the lower activation barrier of its formation. When the volume energy of the particles gets dominant over the surface energy, the metastable form is transformed and the system adopts the modification of lowest energy.     

The Temperature‐Composition Phase Equilibria in the Hg0.8Cd0.2Te‐HgI2 Pseudobinary System

The temperature‐composition phase equilibria of the Hg_0.8Cd_0.2Te‐HgI₂ system were investigated between about 100 and 800 °C using Debye‐Scherrer powder X‐ray diffraction techniques, differential thermal analysis, differential scanning calorimetry, and thermochemical and structural calculations. This system is a pseudobinary temperature‐ composition plane in the HgTe‐CdTe‐HgI₂ pseudoternary phase diagram. Measurable solid solutions of HgI₂ in Hg_0.8Cd_0.2Te with the cubic zinc blende‐type structure exist between about 290 and 700 °C, with a maximum solubility of 4.9 ± 0.3 mole‐% HgI₂ at 363 ± 3 °C. Further addition of HgI₂ to HgI₂‐saturated Hg_0.8Cd_0.2Te yields the formation of CdI₂, which reduces the mole fraction (x) of CdTe in the Hg_1—xCd_xTe host lattice. After sufficient HgI₂ is added, the host lattice is depleted in CdTe and forms Hg₃Te₂I₂ in addition to CdI₂. Phase fields containing the ternary compound Hg₃TeI₄, which we first observed in the HgTe‐HgI₂ system, also exist in the present system. Quaternary analogs of the known ternary compounds Hg₃Te₂I₂ and Hg₃TeI₄, i.e., Hg_3—yCd_yTe₂I₂ and Hg_3—yCd_yTeI₄, were not observed under present experimental conditions.     

Optical damping constants in narrow gap semiconductors

Optical damping constants due to free carriers of HgSe, Zn _x Hg_1–x and Cd _x Hg_1–x Se were estimated from far infrared reflection spectra at 5 and 10 K. The damping mechanism was explained by the Drude type scattering below plasma frequency and by doubly ionized impurity scattering in the higher frequency range.     

Magneto‐Optical Studies of HgTe/HgxCd1−xTe(S) Core–Shell Nanocrystals

The synthesis and magneto‐optical properties of HgTe nanocrystals capped with Hg_xCd_1?xTe(S) alloyed shells have been investigated. The magneto‐optical measurements included the use of optically detected magnetic resonance (ODMR) and circular polarized photoluminescence (CP‐PL) spectroscopy. The PL spectra suggest the existence of luminescence events from both the core HgTe and the Hg_xCd_1?xTe(S) shells. The continuous‐wave (cw) and time‐resolved ODMR measurements revealed that the luminescence at the shell regime is associated with a trap‐to‐band recombination emission. The electron trap is comprised of a Cd–Hg mixed site, confirming the existence of an alloyed Hg_xCd_1?xTe(S) composition. The ODMR data and the CP‐PL measurements together revealed the g‐values of the trapped electron and the valence band hole.     

3‐(Pyridin‐4‐yl)acetylacetone: CdII and HgII compete for nitrogen coordination

3‐(Pyridin‐4‐yl)acetylacetone (HacacPy) acts as a pyridine‐type ligand towards Cd^II and Hg^II halides. With CdBr₂, the one‐dimensional polymer [Cd(μ‐Br)₂(HacacPy)Cd(μ‐Br)₂(HacacPy)₂]_∞ is obtained in which five‐ and six‐coordinated Cd^II cations alternate in the chain direction. Reaction of HacacPy with HgBr₂ results in [Hg(μ‐Br)Br(HacacPy)]_∞, a polymer in which each Hg^II centre is tetracoordinated. In both compounds, each metal(II) cation is N‐coordinated by at least one HacacPy ligand. Equimolar reaction between these Cd^II and Hg^II derivatives, either conducted in ethanol as solvent or via grinding in the solid state, leads to ligand redistribution and the formation of the well‐ordered bimetallic polymer catena‐poly[[bromidomercury(II)]‐μ‐bromido‐[aquabis[4‐hydroxy‐3‐(pyridin‐4‐yl)pent‐3‐en‐2‐one]cadmium(II)]‐di‐μ‐bromido], [CdHgBr₄(C₁₀H₁₁NO₂)₂(H₂O)]_n or [{HgBr}(μ‐Br){(HacacPy)₂Cd(H₂O)}(μ‐Br)₂]_∞. Hg^II and Cd^II cations alternate in the [100] direction. The HacacPy ligands do not bind to the Hg^II cations, which are tetracoordinated by three bridging and one terminal bromide ligand. The Cd^II centres adopt an only slightly distorted octahedral coordination. Three bromide ligands link them in a (2 + 1) pattern to neighbouring Hg^II atoms; two HacacPy ligands in a cis configuration, acting as N‐atom donors, and a terminal aqua ligand complete the coordination sphere. Classical O—H…Br hydrogen bonds stabilize the polymeric chain. O—H…O hydrogen bonds between aqua H atoms and the uncoordinated carbonyl group of an HacacPy ligand in a neighbouring strand in the c direction link the chains into layers in the (010) plane.     

CdSe Spherical Quantum Dots Stabilised by Thiomalic Acid: Biphasic Wet Synthesis and Characterisation

CdSe quantum dots stabilised by thiomalic acid have been synthesised by an aqueous biphasic ligand exchange reaction in air. The materials are completely water‐soluble and were found to be stable over a long time. X‐ray diffraction and transmission electron microscopy reveal the formation of CdSe nanocrystals with cubic structure (a=0.6077 nm; spatial group: F‐43m). The average particle size is about 5 nm. Energy dispersive X‐ray analysis shows that the nanocrystals are nonstoichiometric, with a Cd/Se ratio varying between 60/40 and 70/30, and indicates the presence of Cd²⁺ ions at the nanocrystal surface. Diffuse reflectance infrared Fourier transform measurements suggest that thiomalic acid chelates CdSe through the thiol group and one carboxylic function, while the second COOH group is semi‐free. A complex‐like structure is proposed, in which thiomalic acid forms a five‐membered chelate ring with the Cd²⁺ ions present on the nanocrystal surface. Chelate effect accounts for the easiness of ligand exchange and is expected to additionally stabilise the nanosystem.     

Hydrothermalsynthese und Kristallstruktur der Münzmetall‐Quecksilber‐Chalkogenidhalogenide CuHgSeBr,AgHgSBr und AgHgSI

Hydrothermal Synthesis and Crystal Structure of the Coinage Metal Mercury Chalcogenide Halides CuHgSeBr, AgHgSBr, and AgHgSI The hydrothermal reaction of CuBr and HgSe in concentrated aqueous HBr as solvent at 285 °C yields red crystals of CuHgSeBr, the hydrothermal reaction of AgX (X = Br, I) and HgS in half‐concentrated aqueous HX (X = Br, I) as solvent at 300/400 °C yields yellow crystals of AgHgSBr and AgHgSI. The compounds crystallize isotypically (orthorhombic, Pmma, a = 1020.1(3) pm, b = 431.2(1) pm, c = 925.6(3) pm for CuHgSeBr, a = 964.8(8) pm, b = 466.1(4) pm, c = 942.6(6) pm for AgHgSBr und a = 1015.9(2) pm, b = 464.77(5) pm, c = 984.9(2) pm for AgHgSI, Z = 4). The structures consist of plane folded Hg–Y chains connected by pairs of distorted Y₂X₂ terahedra sharing the X–X‐edge (M = Cu, Ag; X = Br, I; Y = S, Se). Atoms of the monovalent metals M have a strongly distorted tetrahedral coordination of two halogen and two chalcogen atoms. The new structure type shows distinct differences in the arrangement of the Hg–Y chains in comparision to the already known CuHgSeCl, but represents the superposition structure of the order‐disorder phase γ‐Hg₃S₂Cl₂.     

氧化物直接转化法制备汞的硫属化合物纳米材料

以低毒性的HgO与S,Se,Te单质为原料,乙二胺为溶剂,在室温下合成了汞的硫属化合物纳米材料HgS,HgSe和HgTe,并通过XRD,TEM和XPS对产物进行了表征.结果表明,所合成的产物为六方相α-HgS和立方闪锌矿结构的HgSe和HgTe,且纯度高,粒度分布均匀.对反应的机理进行了初步探讨.     

CdTe and anodic oxides on Hg1−xCdxTe: interface and compositional analysis using Rutherford backscattering spectroscopy

The composition and interfacial region has been studied for CdTe and anodic oxides deposited/grown on Hg_1?xCd_xTe using Rutherford backscattering spectroscopy. The interfacial region for the CdTe/Hg_1?xCd_xTe sample was found to be ～35 nm, in which out‐diffusion of Hg was observed. The interfacial region in the case of anodic oxides/Hg_1?xCd_xTe was found to be very small, <10 nm (of the order of experimental resolution), in which the Hg concentration increases steeply and the oxygen concentration decreases. Passivant and bulk compositions also have been obtained in both cases. Copyright © 2005 John Wiley & Sons, Ltd.     

Structural and Solution Studies of two Mercury(II) Complexes with [1,3‐Bis(2‐ethoxy)benzene]triazene

The reaction of [1,3‐bis(2‐ethoxy)benzene]triazene, [ HL ], with Hg(SCN)₂ and Hg(CH₃COO)₂, resulted in the formation of the complexes [Hg L (SCN)] ( 1 ) and [Hg L ₂] · CH₃OH ( 2 ). They were characterized by means of X‐ray crystallography, CHN analysis, FT‐IR, ¹H NMR, and ¹³C NMR spectroscopy. The structure of compound 1 consists of two independent complexes in which the Hg^II atoms are stacked along the crystallographic a axis to form infinite chains. Each Hg^II atom is chelated by one L ligand and one SCN ligand, whereas in compound 2 , the Hg^II atom is surrounded by two L ligands. In addition, 1D chains formed by metal–π interactions are connected to each other by C–H ··· π stacking interactions in the structure of 1 , which results in a 2D architecture. An interesting feature of compound 2 is the presence of C–H ··· π edge‐to‐face interactions.     

Water‐Exchange Mechanism for Zinc(II), Cadmium(II), and Mercury(II) Ions in Water as Studied by Umbrella‐Sampling Molecular‐Dynamics Simulations

Umbrella‐sampling molecular‐dynamics simulations were performed to investigate the water‐exchange reactions of zinc(II), cadmium(II), and mercury(II) ions in aqueous solution. The dissociation of a coordinating water molecule to the M? O distance at 3.34, 3.16, and 3.26 Å for Zn^II, Cd^II, and Hg^II, respectively, leads the system to a transition state. For Zn^II, the first hydration shell is occupied by five spectator water molecules in the transition state, indicating that the water‐exchange reaction proceeds via a dissociative mode of activation. In contrast, the number of spectator water molecules of 5.85 and 5.95 for Cd^II and Hg^II, respectively, suggests an associative exchange for these larger metal ions. The average M? O distance of the spectator molecules is shortened by 0.06 Å for the dissociative exchange of Zn^II, while it is elongated by 0.04 and 0.03 Å for Cd^II and Hg^II, respectively. The water‐exchange rate constants of 4.1×10⁸, 6.8×10⁸, and 1.8×10⁹ s^?1 are estimated for Zn^II, Cd^II, and Hg^II, respectively, at 298 K in terms of the transition‐state theory based on the assumption of a transmission coefficient of unity.     

One‐Pot Synthesis of CdSe Quantum Dots in Aqueous Solution for Biological Labeling

The one‐pot synthesis of water‐soluble and biologically compatible yellow CdSe quantum dots (QDs) featuring the use of glutathione (GSH) as the capping and reducing agent was achieved under aqueous conditions at 150 °C. The synthesized yellow CdSe QDs with quantum yield (QY) up to 20% exhibit zinc blende cubic structure particles with an average diameter of 4‐5 nm. It was found that both molar ratio of Se/Cd and reaction time had a significant effect on size distribution of GSH‐CdSe QDs. Meanwhile, the interaction of QDs bioconjugated to bovine hemoglobin (BHb) was studied by absorption and fluorescence(FL) spectra. With addition of BHb, the FL intensity of CdSe QDs largely quenched due to the static mechanism. The linear range is 5.0 × 10^?8 mol/L to 3.0 × 10^?6 mol/L, and the correlation coefficient is 0.9991, suggesting that could be used as a probe to label biological molecules and bacterial cells.     

One‐ and two‐dimensional CdII coordination polymers constructed from 2‐(2‐methyl‐1H‐benzimidazol‐1‐yl)acetate ligands

The one‐ and two‐dimensional polymorphic cadmium polycarboxylate coordination polymers, catena‐poly[bis[μ₂‐2‐(2‐methyl‐1H‐benzimidazol‐1‐yl)acetato‐κ³N³:O,O′]cadmium(II)], [Cd(C₁₀H₉N₂O₂)₂]_n, and poly[bis[μ₂‐2‐(2‐methyl‐1H‐benzimidazol‐1‐yl)acetato‐κ³N³:O,O′]cadmium(II)], also [Cd(C₁₀H₉N₂O₂)₂]_n, were prepared under solvothermal conditions. In each structure, each Cd^II atom is coordinated by four O atoms and two N atoms from four different ligands. In the former structure, two crystallographically independent Cd^II atoms are located on twofold symmetry axes and doubly bridged in a μ₂‐N:O,O′‐mode by the ligands into correspondingly independent chains that run in the [100] and [010] directions. Chains containing crystallographically related Cd^II atoms are linked into sheets viaπ–π stacking interactions. Sheets containing one of the distinct types of Cd^II atom are stacked perpendicular to [001] and alternate with sheets containing the other type of Cd^II atom. The second complex is a two‐dimensional homometallic Cd^II (4,4) net structure in which each Cd^II atom is singly bridged to four neighbouring Cd^II atoms by four ligands also acting in a μ₂‐N:O,O′‐mode. A square‐grid network results and the three‐dimensional supramolecular framework is completed by π–π stacking interactions between the aromatic ring systems.     

Polykationische Hg‐Pnictid‐Gerüste mit einer neuen Füllungsvariante in den Strukturen von Hg3As2TlCl3 und Hg3Sb2TlBr3

Polycationic Hg‐Pnictide Frameworks with a Novel Kind of Filling in the Structures of Hg₃As₂TlCl₃ and Hg₃Sb₂TlBr₃ Hg₃As₂TlCl₃ and Hg₃Sb₂TlBr₃ were prepared from mixtures of Hg₂X₂, HgX₂ (X = Cl, Br), As or Sb and Tl in sealed evacuated glass ampoules in temperature gradients 330 °C → 290 °C for Hg₃As₂TlCl₃ (red, transparent crystals) and 290 °C → 260 °C for Hg₃Sb₂TlBr₃ (black crystals). The structures of the diamagnetic compounds were determined based on single crystal X‐ray diffraction data. Both compounds crystallize isotypically in the orthorhombic space group Pbcm with Z = 4 and the lattice constants a = 629.2(5) pm, b = 1234.1(7) pm and c = 1224.8(9) pm for Hg₃As₂TlCl₃ and a = 661.0(4) pm, b = 1311.2(9) pm and c = 1307.1(2) pm for Hg₃Sb₂TlBr₃. The structures can be described either as a cubic closest packing of As₂/Sb₂ dumb‐bells and halide anions with all octahedral interstices filled with Hg²⁺ and Tl⁺, or as a polycationic framework (Hg₃Y₂)²⁺ (Y = As, Sb) consisting of pnictide‐pnictide dumbbells each connected by six Hg atoms to a three dimensional porous arrangement. The centers of the cavities are occupied by Tl⁺ ions which are coordinated by six halide ions in distorted octahedral form. These TlX₆ octahedra share corners in all directions in the motive of the ReO₃ structure type. This new structure type shows a close relationship to the cubic family of compounds of the general formula (Hg₆Y₄)[MX₆]X (Y = As, Sb; M = Mo, Ti, Bi, Sb; X = Cl, Br). The halide ions are connected to the Hg atoms of the polycationic network and to the Tl⁺ ions. Extended Hueckel calculations were used to explain the bonding character of the thallium–halide and mercury–halide bonds.     

Charge Separation in Wurtzite/Zinc‐Blende Heterojunction GaN Nanowires

The electronic properties of wurtzite/zinc‐blende (WZ/ZB) heterojunction GaN are investigated using first‐principles methods. A small component of ZB stacking formed along the growth direction in the WZ GaN nanowires does not show a significant effect on the electronic property, whereas a charge separation of electrons and holes occurs along the directions perpendicular to the growth direction in the ZB stacking. The later case provides an efficient way to separate the charge through controlling crystal structure. These results have significant implications for most state of the art excitonic solar cells and the tuning region in tunable laser diodes.     

Template‐Free Preparation of Volvox‐like CdxZn1−xS Nanospheres with Cubic Phase for Efficient Photocatalytic Hydrogen Production

Volvox‐like Cd_xZn_1?xS solid solutions with a cubic zinc blend structure were synthesized through a template‐free ethylene glycol process. Cd(Ac)₂ ? 2 H₂O, Zn(Ac)₂ ? 2 H₂O, and thiourea are used as the starting materials and dissolved in ethylene glycol. These reaction precursors and solvent not only contributed to control over the formation of the volvox‐like spherical geometry, but also exerted vigorous domination for existence of cubic‐phase Cd_xZn_1?xS nanostructures. As‐prepared volvox‐like Cd_xZn_1?xS nanospheres have a diameter of around 100 nm with extensional shells. These samples show excellent photocatalytic H₂ evolution activity from water splitting under visible‐light irradiation without any cocatalyst or scaffolding, owing to their tunable band gap, cubic zinc blend structure, and unique hierarchical porous structure with a high surface area (as high as 95.2 m² g^?1).     

ZnO/ZnS Heterostructured Nanorod Arrays and Their Efficient Photocatalytic Hydrogen Evolution

Semiconducting heterostructures have been widely applied in photocatalytic hydrogen evolution due to their variable band gaps and high energy conversion efficiency. As typical semiconducting heterostructures, ZnO/ZnS heterostructured nanorod arrays (HNRAs) have been obtained through a simple anion‐exchange process in this work. Structural characterization indicates that the heterostructured nanorods (HNRs) are all composed of hexagonal wurtzite ZnO core and cubic zinc‐blende ZnS shell. As expected, the as‐obtained one‐dimensional heterostructures not only lower the energy barrier but also enhance the separation ability of photogenerated carriers in photocatalytic hydrogen evolution. Through comparisons, it is found that 1D ZnO/ZnS HNRAs exhibit much better performance in photocatalytic hydrogen evolution than 1D ZnO nanorod arrays (NRAs) and 1D ZnS NRAs. The maximum H₂ production is 19.2 mmol h^?1 for 0.05 g catalyst under solar‐simulated light irradiation at 25 °C and the corresponding quantum efficiency is 13.9 %, which goes beyond the economical threshold of photocatalytic hydrogen evolution technology.     

Crafting Core/Graded Shell–Shell Quantum Dots with Suppressed Re‐absorption and Tunable Stokes Shift as High Optical Gain Materials

The key to utilizing quantum dots (QDs) as lasing media is to effectively reduce non‐radiative processes, such as Auger recombination and surface trapping. A robust strategy to craft a set of CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS core/graded shell–shell QDs with suppressed re‐absorption, reduced Auger recombination rate, and tunable Stokes shift is presented. In sharp contrast to conventional CdSe/ZnS QDs, which have a large energy level mismatch between CdSe and ZnS and thus show strong re‐absorption and a constrained Stokes shift, the as‐synthesized CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS QDs exhibited the suppressed re‐absorption of CdSe core and tunable Stokes shift as a direct consequence of the delocalization of the electron wavefunction over the entire QD. Such Stokes shift‐engineered QDs with suppressed re‐absorption may represent an important class of building blocks for use in lasers, light emitting diodes, solar concentrators, and parity‐time symmetry materials and devices.     

Phase transformation and optical properties of Cu-doped ZnS nanorods

ZnS nanorods doped with 0-15 mol% of Cu have been prepared by simple solvothermal process. With gradual increase in the Cu concentration, phase transformation of the doped ZnS nanorods from wurtzite to cubic was observed. Twins and stacking faults were developed due to atomic rearrangement in the heavily doped ZnS nanorods during phase transformation. UV-vis-NIR absorbance spectroscopy ruled out the presence of any impure Cu-S phase. The doped ZnS nanorods showed luminescence over a wide range from UV to near IR with peaks at 370, 492-498, 565 and 730 nm. The UV region peak is due to the near-band-edge transition, whereas, the green peak can be related to emission from elementary sulfur species on the surfaces of the nanorods. The orange emission at 565 nm may be linked to the recombination of electrons at deep defect levels and the Cu(t₂) states present near the valence band of ZnS. The near IR emission possibly originated from transitions due to deep-level defects.     

A Novel One‐Dimensional Coordination Polymer Involving Weak Hg?Hg Interactions

The novel, stable, one‐dimensional coordination polymer [Hg₃(dmap)₆(μ‐OAc)₂]_n{(ClO₄)₄}_n ( 1 ; dmap = 4‐(dimethylamino)pyridine) has been synthesized and characterized. Single‐crystal X‐ray analysis showed that the coordination sphere of the two pertinent, zig‐zag‐oriented Hg^II‐atoms is different. One type of Hg‐atom in the N₂O₄Hg HgN₂O₄ environment is seven‐coordinate, with a weak Hg Hg interaction. The other type of Hg^II‐atom in the trans‐HgN₂O₄ units is six‐coordinate.