Fast Doping of Cu into ZnSe NCs by Hydrazine Promoted Cation Exchange in Aqueous Solution at Room Temperature

Controllable doping is an effective way of tuning the properties of semiconductor nanocrystals (NCs). In this work, a simple strategy of fast doping Cu ions into ZnSe NCs under ambient conditions was proposed. The principle of doping is based on hydrazine (N₂H₄) promoted cation exchange reaction. By direct addition of Cu ion stock solution into the preformed ZnSe NCs, Cu doped ZnSe NCs can be obtained. Furthermore, the emission of doped NCs can be tuned by changing the amount of impurity ion addition. The cation exchange reaction is facilitated by three factors: 1) N₂H₄ addition, 2) fast impurity ions, and 3) partial stabilizer removal. The proposed cation exchange reaction in aqueous solution could be an alternate route for NC doping as well as synthesis of ionic NCs.     

The synthesis of Ag/polypyrrole coaxial nanocables via ion adsorption method using different oxidants

Ag/polypyrrole (PPy) coaxial nanocables (NCs) were synthesized by an ion adsorption method. In this method, the pre-made Ag nanowires (NWs) were dispersed in the aqueous solution of copper acetate (Cu(Ac)₂), and the Cu²⁺ ions adsorbed onto the surface of Ag NWs can oxidize pyrrole monomers to polymerize into uniform PPy sheath outside Ag NWs after the Cu(Ac)₂-treated Ag NWs were re-dispersed in the aqueous solution of pyrrole. The morphology of NCs was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). The relationship between the thickness of polymer sheath and the concentration of Cu(Ac)₂ was established. As Cu(Ac)₂ which served as the oxidant can also be replaced by AgNO₃ in this synthesis, the differences on the structure of polymer sheath caused by different oxidants were studied by surface-enhanced Raman scattering (SERS), high-resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Comparing with the characterization results of Ag/PPy NCs synthesized using AgNO₃ as the oxidant which indicates the random arrangement of PPy chains at the interface between polymer sheath and Ag NWs, PPy chain oxidized by Cu²⁺ tends to show a relatively ordered conformation at the interface with the pyrrole rings identically taking the plane vertical to the surface of Ag NWs. In addition, although the main part of the polymer sheath was composed of PPy whatever kind of oxidant was used, the sheath of the NCs oxidized by Cu²⁺ is typical for the existence of Cu(I)–pyrrole coordinate structures with strong Cu(I)–N bond signal shown in XPS characterization.     

Metallophilic Bond‐Induced Quenching of Delayed Fluorescence in Au25@BSA Nanoclusters

The metallophilic bond is a weak interaction between closed‐shell ions and has been widely used a probe for various sensing of toxic chemicals for environmental safety concerns. Here, the interaction between Au nanoclusters (NCs) and metallic ions (mercury (Hg²⁺) and copper (Cu²⁺) ions) is explored using steady‐state and time‐resolved luminescence and transient absorption measurements. For Hg²⁺ ions, the delayed fluorescence (DF) of bovine serum albumin (BSA) protected Au₂₅ (Au₂₅@BSA) NCs is quenched via an effective triplet state electron transfer through the metallophilic bond. However, the Cu²⁺ ions do not alter the DF in Au₂₅@BSA NCs because of the absence of the metallophilic interaction. Furthermore, for Au₈@BSA and Au₁₀@histidine, in which there are no Au⁺ ions on the surface, the fluorescence is not quenched by Hg²⁺ ions. Such a novel triplet electron transfer process through metallophilic bonds are observed and reported for the first time. The reduction of the reverse intersystem crossing is the crucial for Hg²⁺ ion sensing in the fluorescent Au₂₅@BSA NCs.     

Oleylamine‐Assisted Phase‐Selective Synthesis of Cu2−xS Nanocrystals and the Mechanism of Phase Control

Environmentally friendly Cu_2?x S compounds exist in many different mixed phases in nature, while their nanoscale counterparts can be pure phase with interesting localized surface plasmon resonance properties. Because of the complexity of composition and phase, controllable synthesis of Cu_2?x S nanocrystals becomes an important scientific issue in colloidal chemistry. In this work, a hot‐injection method is developed to synthesize Cu_2?x S nanocrystals by injecting a sulfur precursor into a copper precursor using oleylamine and octadecene as solvents. By varying the reaction parameters (temperature, volume ratio of oleylamine/octadecene, molar ratio of Cu/S in the precursors), hexagonal CuS, monoclinic Cu_1.75S, and rhombohedral Cu_1.8S, nanocrystals can be selectively synthesized, providing a platform to illustrate the mechanism of crystal phase control. The crystal phase control of Cu_2?x S nanocrystals is oleylamine‐determined by controlling the molar ratio of Cu/S in the reaction precursors as well as the ratio of Cu_2?x S clusters/Cu⁺ in the subsequent reaction. More importantly, temperature plays an important role in varying the molar ratio of Cu/S and Cu_2?x S clusters/Cu⁺ in the reaction system, which significantly influences the crystal phase of the resulting Cu_2?x S nanocrystals. The understanding into crystal control provides a guideline to realize reproducible phase‐selective synthesis and obtain well‐defined high‐quality materials with precise control.     

Luminescence of CdS:Ag Quantum Dots in a Polymethacrylate Matrix

Semiconductor quantum dots (QDs) exhibit intense luminescence and reproduce optical characteristics. Doping with metal ions has a positive effect on their properties. Introduction of QDs into polymer matrices leads to the formation of a required morphology of composites. There is a problem in synthesis of optically transparent polymer composites containing QDs of the А²В⁶ group that consists in the extremely low solubility of metal chalcogenides and most of their precursors in monomers. To solve this problem, we used colloidal synthesis. CdS QDs were synthesized by the method of appearing reagents in situ in methylmethacrylate (MMA). Doping with Ag⁺ ions was performed by adding a silver salt into the reaction mixture during the synthesis of CdS QDs. The PMMA/CdS:Ag luminescent polymer glasses were synthesized by radical block polymerization of MMA. The transparency of the composites at wavelengths exceeding 500 nm reaches 92% (5 mm). The luminescence excitation is related to the interband electron transitions in CdS crystals. Luminescence in the range of 500–600 nm is observed due to electron relaxation via a system of levels in the band gap of doped CdS crystals. The positions and intensities of the spectral bands depend on the Ag⁺ concentration, particle size, excitation wavelength, and other factors. The formation of Cd(Ag)S/Ag₂S structures at Ag⁺ concentrations higher than 5.0 × 10^–3 mol/L quenches the luminescence.     

Investigation of the electrode/electrolyte interface for the Cu+ ion solid electrolyte N,N′-dimethyl-triethylene diamine-copper(1) bromide

The Cu⁺ ion solid electrolyte 47Cu Br·3(CH₃)₂ C₆H₁₂N₂Br₂ was prepared by hot-pressing and characterised by X-ray analysis and electrical measurements. Novel cell arrangements were used to study the electrochemical behaviour of interfaces between this electrolyte and copper metal and also between this electrolyte and two well known solid solution electrodes (SSEs) for copper, Cu₂Mo₆S_7.59 and Cu_1.8S. The behaviour of the electrolyte/copper interface was correlated with scanning electron microscope (SEM) examinations showing the growth of copper dendrites at the interface. Results from the electrolyte/SSE interfaces showed that there is no interfacial polarisation and that the electrode polarisation is controlled solely by the diffusion of Cu⁺ ions in the SSE. These experiments allowed estimates of the chemical diffusion coefficient for Cu⁺ ions in each material to be made.     

High-Throughput Robotic Synthesis and Photoluminescence Characterization of Aqueous Multinary Copper–Silver Indium Chalcogenide Quantum Dots

The feasibility of a high-throughput robot-assisted synthesis of complex Cu_1-xAg_xInS_ySe_1-x (CAISSe) quantum dots (QDs) by spontaneous alloying of aqueous glutathione-capped Ag–In–S, Cu–In–S, Ag–In–Se, and Cu–In–Se QDs is demonstrated. Both colloidal and thin-film core CAISSe and core/shell CAISSe/ZnS QDs are produced and studied by high-throughput semiautomated photoluminescence (PL) spectroscopy. The silver-copper-mixed QDs reveal clear evidence of a band bowing effect in the PL spectra and higher average PL lifetimes compared to the counterparts containing silver or copper only. The photophysical analysis of CAISSe and CAISSe/ZnS QDs indicates a composition-dependent character of the nonradiative recombination in QDs. The rate of this process is found to be lower for mixed copper-silver-based QDs compared to Cu- or Ag-only QDs. The combination of the band bowing effect and the suppressed nonradiative recombination of CAISSe QDs is beneficial for their applications in photovoltaics and photochemistry. The synergy of high-throughput robotic synthesis and a high-throughput characterization in this study is expected to grow into a self-learning synthetic platform for the production of metal chalcogenide QDs for light-harvesting, light-sensing, and light-emitting applications.     

Nanosize induced effects in luminescent ZnS:Mn2+ quantum dots

Nanocrystals (NCs) of II–VI semiconductors of few nanometers average size, called quantum dots (QDs), are now intensely investigated as radiation detectors. Besides the expected quantum confinement and influence of surface states, our electron paramagnetic resonance investigations of cZnS QDs doped with Mn²⁺ ions, correlated with structural data, underline that other properties should be also taken into consideration in developing the II–VI semiconductor QDs as radiation detectors. Thus, the preferential localization of Mn²⁺ in the core of the cubic ZnS QDs at substitutional Zn²⁺ cation sites next to a stacking lattice defect is expected to lead, besides changes in the impurity energy levels, to specific aggregation properties. An outer shell of different composition can also influence the structural properties of the QDs core with effects on the optical properties as well.     

Effect of laser irradiation on the structure and valence states of copper in Cu-phosphate glass by XPS studies

The effect of laser irradiation using three different wavelengths (IR, visible and UV) generated from Nd:YAG laser on the local glass structure as well as on the valence state of the copper ions in copper phosphate glass containing CuO with the nominal composition 0.30(CuO)-(0.70)(P₂O₅), has been investigated by X-ray photoelectron spectroscopy (XPS). The presence of asymmetry and satellite peaks in the Cu 2p spectrum for the unirradiated sample is an indication of the presence of two different valence states, Cu²⁺ and Cu⁺. Hence, the Cu 2p_3/2 spectrum was fitted to two Gaussian-Lorentzian peaks and the corresponding ratio, Cu²⁺/Cu_total, determined from these relative areas clearly shows that copper ions exist predominately (>86%) in the Cu²⁺ state for the unirradiated glass sample under investigation. For the irradiated samples the symmetry and the absence of satellite peaks in the Cu 2p spectra indicate the existence of the copper ions mostly in Cu⁺ state. The O 1s spectra show slight asymmetry for the irradiated as well as unirradiated glass samples which result from two contributions, one from the presence of oxygen atoms in the P-O-P environment (bridging oxygen BO) and the other from oxygen in an P-O-Cu and PO environment (non-bridging oxygen NBO). The ratio of NBO to total oxygen was found to increase with laser power.     

Mechanistic Aspects of Quantum Dot Based Probing of Cu (II) Ions: Role of Dendrimer in Sensor Efficiency

Selective quenching of luminescence of quantum dots (QDs) by Cu²⁺ ions vis-à-vis other physiologically relevant cations has been reexamined. In view of the contradiction regarding the mechanism, we have attempted to show why Cu²⁺ ions quench QD-luminescence by taking CdS and CdTe QDs with varying surface groups. A detailed study of the solvent effect and also size dependence on the observed luminescence has been carried out. For a 13% decrease in particle diameter (4.3 nm →3.7 nm), the quenching constant increased by a factor of 20. It is established that instead of surface ligands of QDs, conduction band potential of the core facilitates the photo-induced reduction of Cu (II) to Cu (I) thereby quenching the photoluminescence. Taking the advantage of biocompatibility of dendrimer and its high affinity towards Cu²⁺ ions, we have followed interaction of Cu²⁺-PAMAM and also dendrimer with the CdTe QDs. Nanomolar concentration of PAMAM dendrimer was found to quench the luminescence of CdTe QDs. In contrast, Cu²⁺-PAMAM enhanced the fluorescence of CdTe QDs and the effect has been attributed to the binding of Cu²⁺-PAMAM complex to the CdTe particle surface. The linear portion of the enhancement plot due to Cu²⁺-PAMAM can be used for determination of Cu²⁺ ions with detection limit of 70 nM.     

Cu(II)‐catalyzed oxidation of thiols by superoxide ligated to CoIII2

Copper(II) dramatically catalyzes the oxidation of thiols by a superoxide bridging two Co^III ions. The catalyzed path overwhelmingly dominates over the uncatalysed path and is first order in the superoxo complex concentration. The first‐order rate constants show a first‐order dependence in [Cu²⁺], a second‐order dependence in [thiol] and linearly varies with [H⁺]^?3. On the basis of observed kinetics reported here, it is proposed that Cu(II) reacts with two thiol molecules to form a Cu^II(thiol)₂ complex, an electron is transferred from one ligated thiol to the Cu^II center to form Cu^I(thiol) and a thiyl radical. The copper(I)‐thiol complex is oxidized by the conjugate base of the title complex to regenerate Cu^II(thiol). A Cu^II/I catalytic cycle is thus believed to be responsible for the observed catalysis. Copyright © 2012 John Wiley & Sons, Ltd.     

XAFS study of copper and silver nanoparticles in glazes of medieval middle-east lustreware (10th–13th century)

It has recently been shown that lustre decoration of medieval and Renaissance pottery consists of silver and copper nanoparticles dispersed in the glassy matrix of the ceramic glaze. Here the findings of an X-ray absorption fine structure (XAFS) study on lustred glazes of shards belonging to 10th and 13rd century pottery from the National Museum of Iran are reported. Absorption spectra in the visible range have been also measured in order to investigate the relations between colour and glaze composition. Gold colour is mainly due to Ag nanoparticles, though Ag⁺, Cu⁺ and Cu²⁺ ions can be also dispersed within the glassy matrix, with different ratios. Red colour is mainly due to Cu nanoparticles, although some Ag nanoparticles, Ag⁺ and Cu⁺ ions can be present. The achievement of metallic Cu and the absence of Cu²⁺ indicate a higher reduction of copper in red lustre. These findings are in substantial agreement with previous results on Italian Renaissance pottery. In spite of the large heterogeneity of cases, the presence of copper and silver ions in the glaze confirms that lustre formation is mediated by a copper- and silver-alkali ion exchange, followed by nucleation and growth of metal nanoparticles.     

Effect of thermal treatment on linear optical properties of Cu nanoclusters

Silica glass was implanted with 50 keV Cu⁺ ions at various fluences from 6×10¹⁵ to 8×10¹⁶ ions/cm² and thermally-annealed in air between room temperature to 1200 °C. UV/visible spectroscopy measurements reveal absorption bands at characteristics surface plasmon resonance (SPR) frequencies, signifying the formation of copper colloids in silica, even without thermal treatments. Such copper nanoclusters can be attributed to the relatively high mobility of copper atoms, even at ambient conditions. Using the equation derived from the framework of free-electron theory, the average radii of the Cu particles were found to be in the range 2-4 nm from the experimental surface plasmon absorption peaks. Radioluminescence (RL) spectra exhibited broad bands at 410 and 530 nm, associated with the presence of Cu⁺ ions in the as-implanted samples. The effect of thermal annealing in air on absorption and emission spectra of these Cu-implanted samples, as well as the formation of copper nanoclusters from original Cu⁺ ions, is discussed.     

Photoluminescence of Cu-doped and Cu-doped ZnS nanocrystallites

ZnS:Cu⁺ and ZnS:Cu²⁺ nanocrystallites have been obtained by chemical precipitation from homogeneous solutions of zinc, copper salt compounds, with S²⁻ as precipitating anion formed by decomposition of thioacetamide. X-ray diffraction (XRD) analysis shows that average diameter of particles is about 2.0-2.5 nm. The nanoparticles can be doped with copper during synthesis without altering XRD pattern. However, the emission spectrum of ZnS nanocrystallites doped with Cu⁺ and Cu²⁺ consists of two emission peaks. One is at 450 nm and the other is at 530 nm. The absorptive spectrum of the doped sample is different from that of un-doped ZnS nanoparticles. Because the emission process of the Cu⁺ luminescence center in ZnS nanocrystallites is remarkably different from that of the Cu²⁺ luminescence center, the emission spectra of Cu⁺-doped samples are different from those of Cu²⁺-doped samples.     

Improved efficiencies of hybrid organic light‐emitting diodes using efficient electron injection layer

Hybrid organic‐inorganic light‐emitting diodes were developed with pristine ZnO (2.0 wt%) and Cu‐doped ZnO (2.0 wt%) as electron injection layer and iridium(III)‐bis‐2‐(4‐fluorophenyl)‐1‐(naphthalen‐1‐yl)‐1H‐phenanthro[9,10‐d]imidazole (acetylacetonate) [Ir(fpnpi)₂ (acac)] as green emissive layer (521 nm). The pristine ZnO and Cu‐doped ZnO are deposited at indium tin oxide cathode and emissive layer interface. The electroluminescent performances increased by electron injection layer–Cu‐doped ZnO compared with ZnO‐based device because Cu‐doped ZnO injects electron efficiently result in balanced h⁺ ? e^? recombination in emissive layer than ZnO‐based device. The Cu‐doped ZnO (2.0 %) device shows luminance (L) of 10 982 cd/m² at 23.0 V (ZnO, 1450 cd/m² at 23.0 V).     

Fabrication of rare-earth/quantum-dot nanocomposites for color-tunable sensing applications

We developed a new fluorescent nanocomposite by using a layer-by-layer approach to link NaYF₄:Ce,Tb rare-earth (RE) nanocrystals and CdSe/ZnSe semiconductor quantum dots (QDs) with opposite charges. Under ultraviolet light excitation, the nanocomposites exhibited both the green Tb emission centered at 550 nm, and the red QD emission at 650 nm. Sensing applications showed that the red QD emission was quenched by trace amount of Cu²⁺ (or Ag⁺) ions due to the ion displacement mechanism, while the green RE emission kept constant. Thus, the nanocomposites with the decreased QD/RE emission intensity ratio and changed fluorescence output color provided a visible “indicator” to detect metal ions quantificationally. In comparison with single emission materials, the dual emission nanocomposites can be a more reliable probe for various sensing applications.     

Two and four photon absorption and nonlinear refraction in undoped,chromium doped and copper doped ZnS quantum dots

The ZnS quantum dots (QDs) with Cr and Cu doping were synthesized by chemical co-precipitation method. The nanostructures of the prepared undoped and doped ZnS QDs were characterized by UV–vis spectroscopy, Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The sizes of QDs were found to be within 3–5 nm range. The nonlinear parameters viz. Two photon absorption coefficient (β₂), nonlinear refractive index (n₂), third order nonlinear susceptibility (χ³) at wavelength 532 nm and Four photon absorption coefficient (β₄) at wavelength 1064 nm have been calculated by Z-scan technique using nanosecond Nd:YAG laser in undoped, Cr doped and Cu doped ZnS QDs. Higher values of nonlinear parameters for doped ZnS infer that they are potential material for the development of photonics devices and sensor protection applications.     

Systematic theoretical investigation of structure and electronic properties of pure copper and lithium doped copper clusters

The pure copper and lithium-doped copper clusters are studied using the unbiased CALYPSO structure searching method and density function theory to understand the evolution of various structure and electronic properties. Theoretical results show the growth behaviours of doped clusters are organised as follows: Li capped Cu_n clusters or Li substituted Cu_n+1 clusters as well as Cu capped Cu_n-1Li clusters. Moreover, the lowest energy structures of Cu_nLi favour planar structures for n ≤ 3 and three-dimensional structures for n = 4–12. In addition, the calculated averaged binding energies, fragmentation energies and second-order difference of energies exhibit obvious odd–even alternations as cluster size increasing. At last, the highest occupied-lowest unoccupied molecular orbital gaps, molecular orbital energy, magnetic property, natural population analysis, natural electron configurations, electrostatic potential, electron density difference, Infrared and Raman spectra and density of states are also, respectively, operative for characterising and rationalising the electronic properties of doped clusters.     

Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

Synthesis and characterization of Cu doped ZnS nanoparticles using TOPO and SHMP as capping agents

Undoped and Cu²⁺ doped (0.2-0.8%) ZnS nanoparticles have been synthesized through chemical precipitation method. Tri-n-octylphosphine oxide (TOPO) and sodium hexametaphosphate (SHMP) were used as capping agents. The synthesized nanoparticles have been analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrometer, photoluminescence (PL) and thermo gravimetric-differential scanning calorimetry (TG-DTA) analysis. The size of the particles is found to be 4-6 nm range. Photoluminescence spectra were recorded for ZnS:Cu²⁺ under the excitation wavelength of 320 nm. The prepared Cu²⁺-doped sample shows efficient PL emission in 470-525 nm region. The capped ZnS:Cu emission intensity is enhanced than the uncapped particles. The doping ions were identified by electron spin resonance (ESR) spectrometer. The phase changes were observed in different temperatures.