ZnO:HCl single crystals: Thermodynamic analysis of CVT system,feature of growth and characterization

The full thermodynamic analysis of using HCl as a chemical vapor transport (CVT) agent (TA) for ZnO single crystals growth in closed growth chambers, including 16 chemical species, is carried out for wide temperature and loaded TA pressure ranges. The influence of the growth temperature, of the TA density and of the undercooling on the rate of ZnO mass transport was investigated theoretically and experimentally. It is shown that the mass transport is diffusion-limited at about 1050 °C, and it is limited by kinetics of the CVT reaction at lower temperatures. It is experimentally shown that using HCl favors obtaining void-free n-ZnO crystals with controllable electrical parameters, it reduces the effect of adhesiveness to the walls of the growth chamber. The characterization by the photoluminescence spectra, the transmission spectra and the electrical properties in the wide temperature range allowed analyzing energy spectra of Cl-containing stable defects in ZnO and electrical activity of Cl donors. Some methods of activation energy correction for Cl-containing centers are discussed.     

Syntheses,structures, luminescent and magnetic properties of two coordination polymers based on a fl exible multidentate carboxylate ligand

Two coordination polymers,{[Cu_3(tci)_2(DMAc)_3]-6DMAc 2H_2O}_n(1) and {[Cu_3(tci)_2(tpt)_2(H_2O)_2].2DMAc-2H_2O}_n(2)(H_3tci = tris(2-carboxyethyI)isocyanurate,tpt = 2,4,6-tris(4-pyridyl)-l,3,5-triazine,DMAc = N,/V-dimethylacetamide),have been constructed under solvothermal conditions.Both polymers were structurally characterized by single crystal X-ray diffraction,elemental analyses,IR spectra,thermogravimetric(TG) analyses and powder X-ray diffraction(RXPD).1 shows a(3,4)-connected 2D layer structure comprising Cu_2(CO_2)4 paddle-wheel units,which are further bridged by C-H…O interactions to give a 3D supramolecular network.The introduction of tpt produces different framework for 2 that comprises a dinuclear and a mononuclear Cu(Ⅱ) building units,which are further bridged together by tci~(3-) and tpt ligands to give a 4-connected 2D topological net.Adjacent 2D layers are packed together via C-H…O interactions and π…π stacking interactions to form a 3D supramolecular structure.In addition,the luminescent properties and the solid-state UV-vis spectra of 1 and 2 were explored.Furthermore,antiferromagnetic exchange interactions were unveiled in the Cu_2(COO)_4 units of 1.     

Zinc coordination polymers with rigid dicarboxylates and semirigid 3,5-bis(imidazole-1-yl) pyridine: syntheses,structural topologies,and luminescent properties

Two metal coordination polymers, {[Zn(bpdc)(bip)]·2H₂O}_n (1) and [Zn(tdc)(bip)] (2) [H₂bpdc?=?biphenyl-4,4’-dicarboxylate, H₂tdc?=?thiophene-2,5-dicarboxylate, bip?=?3,5-bis(imidazole-1-yl)pyridine], have been synthesized and characterized by IR, elemental analysis, XRD, and X-ray single-crystal diffraction. In 1, bpdc and bip link Zn(II) ions into a corrugated 2D layer. The corrugated 2D layers polycatenate each other, yielding a 2D→3D polycatenation net. In 2, dinuclear Zn(II) units are formed by bip and further connected by tdc to construct a 2D 3-connected framework. The luminescent properties of 1 and 2 are investigated in the solid state at room temperature.     

New heterometallic coordination polymers based on zinc(II) complexes with Schiff-base ligands and dicyanometallates: synthesis,crystal structures,and luminescent properties

Four new d¹⁰ heterometallic coordination polymers have been obtained using three Schiff-base ligands, zinc(II) nitrate, and dicyanometallates: ₁^∞[{Zn₃(Salen)₂}{μ-Au(CN)₂}₂] (1); ₁^∞[Zn(Saldmen){μ-Ag(CN)₂}]·2H₂O (2); ₁^∞[Zn(Salampy){μ-Ag(CN)₂}] (3); ₁^∞[Zn(Salampy){μ-Au(CN)₂}] (4). The Schiff bases are obtained from condensation of salicylaldehyde with ethylenediamine (H₂Salen); N,N-dimethyl-ethylenediamine (HSaldmen) and, respectively, 2-aminomethyl-pyridine (HSalampy). The dicyanometallates are K[Ag(CN)₂] and K[Au(CN)₂]. The compounds were characterized by X-ray single-crystal diffraction, infrared spectroscopy, UV–vis spectroscopy, and elemental analysis. In compound 1, the homotrimetallic units, {Zn₃(salen)₂}²⁺, are connected by two [Au(CN)₂]^? bridges, forming a 1-D double chain. In compounds 2–4, the crystal structures show polymeric zigzag chains generated by the mononuclear zinc(II) nodes and [M(CN)₂]^? spacers. The luminescence properties of the new heterometallic polymers have also been investigated.     

Nanostructure and luminescent properties of sol-gel derived europium-doped amine functionalised hybrids

The effect of doping by europium triflate on the nanoscopic structure of organic-inorganic hybrid formed by a siliceous network containing pendant amine-terminated propyl chains, called aminosils, was investigated by Small-Angle X-ray Scattering (SAXS). It appears that the composites exhibit a two-level structure. The first level consists of well-condensed cubic-like siloxane octamers, with a radius of gyration around 2 Å. The second level is formed by the aggregation of these siloxane nanodomains to form larger structures, in which the nanodomains are spatially correlated and separated by the organic pendant chains. Europium doping inhibits the aggregation between siloxane octamers, leading to a less compact second-level structure. This can be explained by the Eu³⁺ coordination close to the external surface of the siloxane nanodomains, as detected by luminescence spectroscopy.     

Syntheses,crystal structures,and magnetic and luminescent properties of a series of lanthanide coordination polymers with chelidamic acid ligand

A series of lanthanide(III) complexes with chelidamic acid ligand, [Ln(C₇H₂NO₅)·3H₂O]_n·nH₂O (Ln = La (1), Y (2), Sm (3), and Nd (4)), [Gd₂(C₇H₂NO₅)₃·4H₂O]_n·2nH₂O (5) and [Ce(C₇H₂NO₅)·1.5H₂O]_n (6), have been synthesized by hydrothermal method and structurally characterized by single-crystal X-ray diffraction. Complexes 1–4 are isostructural and possess 2D framework. Complex 5 contains two different Gd(III) ions linked through carboxylate group to form a 2D framework. Complex 6 exhibits a (4⁴) topology 2D network. The variable-temperature magnetic properties of 3 and 5 have been investigated. Furthermore, the photoluminescent properties of 1, 2, 3, and 5 at room temperature were also studied.     

Complex wurtzite ZnSe microspheres with high hierarchy and their optical properties

Complex wurtzite ZnSe microspheres with hierarchical fractal structure and showing strong quantum-size effects can be prepared easily by a mild solvothermal reaction in a diethylenetriamine (DETA)-deionized water (DIW) binary solution. The ZnSe microspheres are made up of nanosheets, each formed by the face-to-face pairing of two individual nanosheets. In addition, high-order, flowerlike hierarchical structures are formed by the attachment of flexible, uniform nanofibers to the exposed faces of each nanosheet pair. The surface morphology of the nanosheets changed as reaction time increased and the detailed phase-transformation and shape-evolution processes were studied. This approach could provide an effective strategy for tuning the electronic and optical properties of semiconductors, with special advantages over the traditional high-temperature approach, and could be extended to access other semiconductor materials with unusual morphologies and structures.     

Synthesis, crystal structures, magnetic and luminescent properties of unique 1D p-ferrocenylbenzoate-bridged lanthanide complexes

Treatments of p-ferrocenylbenzoate [p-NaOOCH₄C₆Fc, Fc=(η⁵-C₅H₅)Fe(η⁵-C₅H₄)] with Ln(NO₃)₃·nH₂O afford seven p-ferrocenylbenzoate lanthanide complexes {[Ln(OOCH₄C₆Fc)₂(μ₂-OOCH₄C₆Fc)₂(H₂O)₂](H₃O)}_n [Ln=Ce (1), Pr (2), Sm (3), Eu (4), Gd (5), Tb (6) and Dy (7)]. X-ray crystallographic analysis reveals that the isomorphous complexes {[Ce(OOCH₄C₆Fc)₂(μ₂-OOCH₄C₆Fc)₂(H₂O)₂](H₃O)}_n (1) and {[Pr(OOCH₄C₆Fc)₂(μ₂-OOCH₄C₆Fc)₂(H₂O)₂](H₃O)}_n (2) form a unique 1D double-bridged infinite chain structure bridged by μ₂-OOCH₄C₆Fc groups. Each Ln(III) ion adopts a dodecahedron coordination environment with eight coordinated oxygen atoms from two terminal monodentate coordinated FcC₆H₄COO⁻ units, two terminal monodentate coordinated H₂O molecules and four μ₂-⁻OOCH₄C₆Fc units. The luminescent spectra reveal that only 4 and 6 exhibit characteristic emissions of lanthanide ions, Eu(III) and Tb(III) ions, respectively. The variable-temperature magnetic properties of 5 and 7 suggest that a ferromagnetic coupling between spin carriers may exist in 5.     

X-ray structure and temperature dependent luminescent properties of two bimetallic europium complexes

The structural, luminescent and temperature dependent luminescent properties of two homodinuclear europium complexes bridged by 2,2′-bipyrimidine (bpm) are reported. β-Diketonate ligands 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (tfa) and 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (tta) are used as capping ligands resulting in complexes of the form [Eu(tfa)₃]₂bpm (1) and [Eu(tta)₃]₂bpm (2). All Eu^III ions are eight coordinate with six O atoms from the β-diketones and two N atoms from the polyazine bridging ligand. Excitation of the β-diketonate ligands tfa or tta at ca. 340 nm in toluene solutions results in the characteristic Eu^III emission in the visible region of the spectrum. The emission intensity and lifetime associated with the Eu^III centers decrease as the temperature of the solution is increased. Lifetime measurements are fit to a monoexponential while the temperature dependent lifetime data is fit to an Arrhenius-type equation. Evaluation of the data in comparison to data obtained from the monometallic Eu^III analogs reveal very similar photoluminescent properties. This suggests little electronic communication between Eu^III ions via the polyazine bpm bridging ligand.     

Magnetic and structural investigation of Mn(2+)-doped ZnSe semiconductor nanoparticles.

X-ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals were carried out to study the local electronic structure and magnetic properties of Mn(2+) embedded in the lattice of ZnSe nanoparticles. It is shown that Mn(2+) is exclusively present in the bulk of ZnSe nanoparticles. Neither Mn-Mn coupling nor traces of oxidation to higher Mn oxidation states was observed. This result, which is consistent with EPR spectroscopic data, provides clear proof of the location of Mn(2+) in semiconductor nanoparticles. Further, it is shown that the magnetic ions are highly polarised inside the nanocrystals, where they reach about 50 % of the theoretical value of a pure d(5) state under identical conditions.     

The luminescent properties of divalent europium complexes of crown ethers and cryptands

The luminescent properties of divalent europium complexes with crown ether, azacrown ether, N-pivot-azacrown ether, and cryptand in methanol or water have been systematically investigated under UV irradiation. These divalent europium complexes show greatly enhanced emission from 417 nm to 488 nm in the visible blue region in comparison with that of the methanol solution of EuCl₂. The aqueous solution of EuCl₂ is non-luminescent. This obvious distinction in luminescent properties between the macrocyclic ligand-coordinated divalent europium and uncoordinated divalent europium is attributed to the “insulation effect” of Eu²⁺ ion from the solvent molecules of CH₃OH and H₂O by the macrocyclic crown ether or cryptand encapsulation to divalent europium. Moreover, these macrocyclic ligands provide an additional restriction to the electronic charge expansion of the excited Eu²⁺. This also contributes to the enhancement of the Eu²⁺ luminescence. Among all the investigated macrocyclic ligands, 15-crown-5 (15C5) affords the largest enhancement to the Eu²⁺ emission. The intensity of the Eu²⁺–15C5 complex is 690 times that of the EuCl₂ methanol solution with the same Eu²⁺ concentration. This special emission enhancement effect is related to the particular complex composition of 1:3 (Eu²⁺:15C5) and corresponding configuration of Eu²⁺–15C5 complex in methanol. Concerning the mechanism, the luminescence enhancement of divalent europium by complexation with these macrocyclic crown ether or cryptand ligands is found to be initiated from the decrease in non-radiative rate constant rather than from the increase in radiative one.

The divalent europium complexes of methacrylate polymeric polyether derivatives such as 15C5-, 18-crown-6- (18C6), and cryptand [2.2.1]- or [2.2.2]-containing polymer and copolymer have also been prepared. Their luminescent properties in solid state have been studied to aim for practical application. As a similar situation to the simple polyether complexes, the divalent europium complex with 15C5-containing polymer or copolymer shows the largest luminescent enhancement effect. Its emission intensity reaches about 20% that of the commercial inorganic luminescence product CaWO₄:Pb (NBS 1026). In addition, the doping effect of several divalent ions, namely Mg, Sr, Ba and Zn in polymeric complexes, has also been investigated according to the luminescence concentration quenching mechanism in solid state luminescence materials. The emission intensity of 15C5-containing polymer europium(II) complex is raised to twice stronger by doping of Zn²⁺ ion.     

The architectures of 1D coordination polymers with the versatile 7-chloroquinoline-4-alanine ligand mediated by anions: Syntheses,structures and luminescent properties

Three new coordination polymers, [Cd(cqaH)(cqa)Cl]_n (1), [Cd(cqaH)(cqa)Br]_n (2) and {[Cd₂(cqa)₄] · 3H₂O}_n (3) (Hcqa = 7-chloroquinolin-4-alanine, cqaH = the Hcqa ligand, where the proton is transferred from the acid group to the imine group) have been prepared under hydrothermal conditions and characterized by X-ray structural analyses. Both complexes 1 and 2 possess 1D ribbon-like chains, and complex 3 features a 1D double-stranded chain. Various coordination fashions and supramolecular networks are observed in complexes 1–3 due to the versatile coordination modes of the ligand and the cooperative effect from anions in the assemblies. In addition, the luminescent properties for all compounds have been investigated in the solid state.     

A bright blue emission material based on anthracene： Synthesis, characterization and luminescent properties

A blue light-emitting material,2-(N-ethyl-anthraceneyl-9) imidazo[4,5-f]1,10-phenanthroline(EAIP),has been synthesized and characterized by ~1H NMR,IR,elemental and single crystal X-ray diffraction analysis.The results of theoretical calculations indicate that the HOMO and LUMO distributions mainly locate at the anthracene fragment.It displays bright blue emission in both solid state and dichloromethane solution.The emission quantum yield calculated is 0.76.     

Synthesis and peptide-binding properties of a luminescent pyrimidine zinc(II) complex

The synthesis and peptide-binding properties of a Zn(II)nitrilotriacetate complex substituted with pyrimidine hydrazine amides are reported. The metal complex provides millimolar binding affinity in aqueous buffer to peptides bearing N-terminal His. The pyrimidine heterocycles intermolecularly interact with the bound peptide and quench the emission of nearby Trp residues by energy transfer.     

Mg and Ni Incorporated ZnO Diluted Magnetic Semiconductor for Magnetic and Photo-Catalytic Applications

Zinc oxide is recently being used as a magnetic semiconductor with the introduction of magnetic elements. In this work, we report phase pure synthesis of Mg and Ni co-substituted ZnO to explore its structure, optical, magnetic and photo-catalytic properties. X-ray diffraction analysis reveals the hexagonal wurtzite type structure having P63mc space group without any impurity phase. UV-Vis spectrophotometry demonstrates the variation in bandgap with the addition of Mg and Ni content in ZnO matrix. Magnetic measurements exhibit a clear boosted magnetization in Ni and Mg co-doped compositions with its stable value of bandgap corroborating the structural stability and magnetic tuning for its advanced applications in modern-day spintronic devices. Photo-catalytic measurements performed using methyl green degradation demonstrate an enhanced trend of activity in Mg and Ni co-doped compositions.     

Synthesis and luminescent properties of polymeric metal complexes containing bis(8-hydroxyquinoline) group

A novel ligand: 4,4′-bis(8-hydroxyquinoline-5-propenyl)-biphenyl (B8QPB) (1), has been synthesized by Witting-Horner reaction, and the corresponding two polymeric metal complexes were also prepared by polynuclear of the ligand with aluminium (III) (2) and zinc (II) (3) halides, respectively. The structure of the ligand was characterized by ¹H NMR, FT-IR and elemental analysis techniques; polymeric metal complexes were characterized by FT-IR, UV-vis, elemental analysis techniques, conductivity measurements and gel permeation chromatography (GPC). The results indicate that the stoichiometry of polymeric metal complexes is [(C₃₄H₂₄O₂N₂)₁₁Al₁₂Cl₂₈] and [(C₃₄H₂₄O₂N₂)₃₂(ZnCl₂)₃₃]. B8QPB coordinated with metal ions to form polymers. The luminescence properties of the complexes 1-3 were investigated by UV-vis and fluorescence spectra at room temperature. The experimental results show that polymeric metal complexes 2 and 3 emit blue/green luminescence at 514 and 504 nm in the solid state and at 470 and 507 nm in DMSO solution. Thermal properties measurement and analysis show that they have good thermal stabilities.     

Photochromic bipyridyl metal complexes: Photoregulation of the nonlinear optical and/or luminescent properties

The combination of transition metals and ligands featuring photochromic units is receiving much attention and opens up new perspectives for the design of metal-based photoswitchable molecules. This account summarizes some of our recent works made in the area of photochromic organometallic and coordination compounds, which have been used for the photomodulation of the quadratic non-linear optical (NLO) properties, as well as of the photoregulation of the emission properties of the resulting systems. For this purpose, we have designed new chromophores combining dithienylethene (DTE)-based bipyridine ligands with different metallic fragments (Re^I, Fe^II, Ru^II, Ir^III, Cu^I, Zn^II), giving rise to multi-photochromic metal complexes containing from two to six DTE units, and studied the photocontrol of both NLO and luminescence properties.     

Holmium porphyrin compound liquid crystals: Synthesis and properties

5,10,15,20-Tetra-[(p-alkoxy-m-ethyloxy)phenyl]porphyrin and [5-(p-alkoxy)phenyl-10,15,20-tri-phenyl]porphyrin and their holmium(III) complexes are reported. They display a hexagonal columnar discotic columnar (Col_h) liquid crystal phase and were studied by cyclic voltammetry, surface photovoltage spectroscopy (SPS), electric-field-induced surface photovoltage spectroscopy (EFISPS) and luminescence spectroscopy. Within the accessible potential window, all these compounds exhibit two one-electron reversible redox reactions. Quantum yields of Q band are in the region 0.0045–0.21 at room temperature. The SPS and EFISPS reveal that all the compounds are p-type semiconductors and exhibit photovoltaic response due to π–π^* electron transitions.