Influence Of Cu Ions Research Articles

Copper-Doped Zinc Oxide Nanoparticles for the Fabrication of white LEDs

Zinc oxide (ZnO) is the most commonly and widely studied material in the field of nano science and technology due to its unique characteristics, such as wide band gap energy (3.37 eV), electrical and thermal stability, large exciton binding energy (60 meV), biocompatibility and biosafety. Copper is considered as an important dopant for ZnO due to their almost similar ionic radii which enhances the properties of ZnO. Thus, pure and copper-doped nanocrystalline ZnO particles were synthesized through sol–gel approach in the current study. The concentration of the dopant is varied from (0.1–0.3%) and the composition, structural and optical characterizations were performed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, UV-Vis optical absorption and photoluminescence (PL) spectrometer. The structural analysis confirmed that copper ions substitute Zn ions without altering their wurtzite structure and a crystallite size of 10–16 nm with high degree of crystallization. Morphological properties conducted using SEM confirmed copper doping strongly influenced the grain size and morphology of ZnO NPs. Moreover, the morphology variation is observed from spherical nanoparticles to nanorods with Cu (0.2%) doping into host matrix. The morphological variation may be attributed to strong influence of Cu ions on the growth rate of ZnO. PL measurement had been carried out at room temperature in which high intensity broad emission peaks were observed in visible region around 450–700 nm that indicates the superposition of green and yellow-orange emission bands. Currently, light-emitting diodes (LEDs) giving green light emission have been combined with broad-band visible phosphors to make white-light LEDs. Thus, green photo luminescent copper-doped ZnO nanoparticles from the current study is highly significant in the fabrication of white-light LEDs.

Influence of Cu ions on the photo‐transport properties in KTaO3:(Cu,V) single crystals

AbstractPhotoconductivity kinetics, temperature dependence and excitation spectra were measured in the intervals 15‐300 K and 2‐4.2 eV in KTaO3:(Cu,V) single crystals processed by oxidation/reduction treatments. The kinetics, excited by band‐gap excitation, present very slow saturation times, while faster time responses were observed using excitation below the band‐gap. The oxidized crystal exhibited higher photoconductivity when Elight > 3 eV. Linear dependence on light intensity was measured, suggesting one center recombination processes. Optical absorption at room temperature was checked as complementary information. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic transition and conducting behavior of the Cu-doped LaMn1－xCuxO3 system

The magnetic transition and conducting behaviors of LaMn1-xCuxO3 (x=0.05, 0.1, 0.2, 0.3, 0.4) system have been systematically studied. The results show that very small amount of Cu-doping (x=0.05) into the anti-ferromagnetic LaMnO3 matrix induces strong ferromagnetic transition below about 157K. The Curie temperature decreases gradually with the increase of Cu-doping content, while the magnetization increases firstly and then decreases. In accordance with the magnetic properties, the electrical resistivity decreases at low dopant (x≤0.10) and then increases with the increase of Cu-doping content. All samples exhibit insulating conducting behavior in the whole temperature range: from a paramagnetic insulator to a ferromagnetic insulator. The conducting behavior of lower doped samples (x≤0.10) is well fitted by the Mott Variable Range Hopping (VRH) model,and then favors to the thermoactivation model when 0.10≤x≤0.40. With the increase of Cu-doping content, the influence of Cu ions on the double exchange interaction among the Mn-O-Mn chains and the magnetic structure results in that the eg electron transport obeys the domination of potential barrier in the VRH model at lower doping and then favors the domination of energy gap in the thermal activation model at higher doping contents.

Electrochemical removal of nitrate ions in waste solutions after regeneration of ion exchange columns

Electrochemical reduction of nitrate ions in synthetic regenerating solutions after ion exchange column regeneration was studied. The influence of current density on the current efficiency was determined in the range 2.8–7.6 mA cm−2 in a diaphragmless flow-through electrolyser in a batch recirculation mode. A Cu cathode and a Ti/Pt anode was used, the temperature being maintained at 25 ∘C. Highest integral current efficiency occurred at 2.8 mA cm−2. The presence of about 6 mg dm−3 Cu ions in treated solution was found to prevent a decrease in cathode activity and, consequently, in electrolysis efficiency. The catalytic influence of Cu ions was verified by potentiodynamic polarisation experiments on a copper rotating disc electrode and by chronopotentiometry performed during the course of electrolysis.