Co-doped Zinc Research Articles

Combustion synthesis of a blue Co-doped zinc aluminate near-infrared reflective pigment

A near-infrared reflective blue pigment with a low cobalt content, Zn0.9Co0.1Al2O4, was prepared by solution combustion synthesis, which proved to be time-effective and energy-efficient. No additional annealing was required as the elevated temperature developed during the exothermic self-propagating combustion reaction (1428 °C) enabled the direct formation of a Zn0.9Co0.1Al2O4 solid solution having an appealing blue color: L* = 67.9, a* = −3.7, b* = −39.0. The resulting blue pigment had an average particle size of 6.1 μm and a BET surface area of 6.5 m2/g. The total solar reflectance of the pigment (63%) recommends the use of Zn0.9Co0.1Al2O4 as a near-infrared reflective blue pigment for cool coatings. The ability of the pigment to reflect the near-infrared radiation was confirmed by measuring the surface temperature of an aluminum sheet painted with an acrylic coating containing 30 % wt. pigment, that had a total solar reflectance of 59%. The excellent properties of Zn0.9Co0.1Al2O4, color and solar reflectance, together with the low cobalt content and the advantages of self-propagating combustion reaction recommend the use of combustion synthesis for the preparation of blue Zn0.9Co0.1Al2O4 near-infrared reflective pigments.

Photocatalytic activity of Ag-N co-doped ZnO nanorods under visible and solar light irradiations for MB degradation

Zinc oxide nanorods (CZ), silver-doped zinc oxide nanorods (CAZ), nitrogen-doped zinc oxide nanorods (CNZ), and silver-nitrogen co-doped zinc oxide nanorods(CANZ) were synthesized using the chemical precipitation method. The as-synthesized nanorods were characterized using x-ray diffraction (XRD); scanning electron microscopy (SEM), and UV–vis spectroscopy (UV–vis). The photocatalytic degradation of methylene blue (MB) was studied using the as-synthesized nanorods under both solar and visible light irradiations. CANZ has the highest photocatalytic activity under both visible as well as solar light irradiations; with CNZ, CAZ and CZ show a decreasing order in their photocatalytic activities. In addition to this, the photocatalytic activity of the as-synthesized nanorods was compared under both light sources. The photocatalytic activity of all the nanorods is higher under solar light as compared to the visible light irradiation. Therefore, sun light is the best light source for the removal of dyes from the environment.

First-principles study on the electronic and optical properties of Si and Al co-doped zinc oxide for solar cell devices

Electronic and optical properties of co-doped zinc oxide ZnO with silicon (Si) and aluminum (Al), in Zn1−2x Si x Al x O (0 ≤ x ≤ 0.0625) original structure forms, are investigated by the first-principles calculations based on the density functional theory (DFT). The optical constants and dielectric functions are investigated with the full-potential linearized augmented plane wave (FP-LAPW) method and the generalized gradient approximation (GGA) by WIEN2k package. The complex dielectric functions, refractive index and band gap of the pure as well as doped and co-doped ZnO were investigated, which are in good agreement with the available experimental results for the undoped ZnO. Thus, the maximum optical transmittance of the co-doped ZnO of about 95 % was achieved; it is higher than that of pure ZnO. Thus, we showed for the Si–Al co-doped ZnO with x = 0.0315 that the optical transmittance can cover a larger range in the visible light region. In addition, an occurrence of important energy levels around Fermi levels was showed, which is mainly due to doping atoms that lead to an overlap between valence and conduction bands, and consequently to the significant conductor behavior of the Si–Al co-doped ZnO. The original Zn1−2x Si x Al x O structure reveals promising optical and electronic properties, and it can be investigated as good candidates for practical uses as transparent and conducting electrodes in solar cell devices.

P-55: Ga and In Co-Doped Zinc Oxide Films Deposited on Flexible High Gas Barrier Films for Transparent Conductive Electrode

We developed the highly moisture resistance Zinc Oxide films on flexible high gas barrier PEN substrates. After the damp test, changing ratio of sheet resistance were 1.02, this value can be applied the flexible device electrode. We studied the structural, optical and electrical properties of Zinc Oxide films in detail. After a damp test at 60 °C, 95%RH for 1000 h, sheet resistance of 200 nm thickness GIZO film on deposited plastic high gas barrier substrate was 30 ohm/sq., and changing ratio of sheet resistance, before and after damp test value was 1.02.

Application of Aliumium and Lanthanum Co-doped Zinc Oxide Infrared Stealth Coating on Tent Fabrics

Application of Aliumium and Lanthanum Co-doped Zinc Oxide Infrared Stealth Coating on Tent Fabrics

Structural, linear and nonlinear optical properties of co-doped ZnO thin films

Different compositions of Co-doped zinc oxide [(Zn(1−x)Co x O) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple–DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy (E o), the dispersion energy (E d), and the static refractive index (n 0), were determined. The nonlinear refractive index of the Zn(1−x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.

Fabrication and characterization of optical and electrical properties of Al–Ti Co-doped ZnO nano-structured thin film

Al and Ti Co-doped zinc oxide (ATZO) nano-structured thin films with 1 at % Al and 0.1 at % Ti were deposited on glass substrate via sol–gel technique. X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) methods were used to investigate the structure, morphology and surface roughness of the thin films. The optical properties were investigated by spectroscopic ellipsometry (SE) and UV-VIS spectrophotometer. The resistivity measurement was performed using a LCR-meter. XRD analysis confirmed the zinc oxide hexagonal wurtzite structure for the thin films. It was found that Ti doping reduces the roughness and grain size values to 8.2 nm and 50 nm, respectively. The optical band gap energy was concluded to be 3.23 eV for ZnO film and it increases to 3.26 eV for ATZO films. Refractive index decreased upon Ti doping as a consequence of increase in charge carrier concentration. All the thin films exhibit high transmittance over 85% in the visible wavelength region. Ti replacement causes to decrease in resistivity and minimum resistivity value of 13 × 106 Ωcm was measured for ATZO thin film.

Effect of hydrogen doping on the properties of Al and F co-doped ZnO films for thin film silicon solar cell applications

Aluminum and fluorine co-doped zinc oxide (AFZO) thin films were prepared in Ar+H2 atmospheres by rf magnetron sputtering at room temperature. The structural, electrical, and optical properties of the prepared films were investigated using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Hall-effect measurement, X-ray photoelectron spectroscopy, and ultraviolet–visible spectrometry, and their dependence on deposition atmosphere (i.e. H2/(H2+Ar) ratio) was studied. The resulting films showed a (0 0 2) diffraction peak, indicating a typical wurtzite structure, and the optimal film crystallinity was obtained with the H2/(H2+Ar) ratio of 3%. The electrical resistivity of AFZO films decreased to 9.16×10−4Ω-cm, which was lower than ZnO:Al and ZnO:F films due to double doping effect of Al and F. The resistivity further decreased to below 5×10−4Ω-cm for the AFZO film with the H2/(H2+Ar) ratio of 3%–5%. All the films regardless of hydrogen content displayed high transmittances (>92%) in the visible wavelength range. Applying the developed AFZO films as front transparent electrodes, amorphous Si thin film solar cells were fabricated and the open-circuit voltage, fill factor, and efficiency of the cell with the hydrogenated AFZO film were improved in contrast to those without the hydrogenated film.

Cr-N co-doped ZnO nanoparticles: synthesis, characterization and photocatalytic activity for degradation of thymol blue

Here we report the synthesis of CrN co-doped ZnO for the first time. Zinc oxide (ZnO) nanoparticles were synthesized by direct precipitation method via the reaction between zinc nitrate [Zn(NO 3 ) 2 .6H 2 O] and ammonium carbonate [(NH 4 ) 2 CO 3 ] in aqueous solutions with proper concentration. Modified photocatalysts were synthesized by the incipient wetness impregnation method (chromium-doped ZnO) and by solid state reactions using ZnO and urea as precursors (nitrogen-doped ZnO). Chromium-nitrogen co-doped ZnO nanomaterials were prepared from the already prepared N-doped ZnO nanomaterials via one step impregnation method. The as-synthesized photocatalysts were investigated by XRD, BET, SEM-EDX, FTIR, and UV–Vis techniques. Photocatalytic degradation of thymol blue using as-synthesized photocatalysts was studied under visible as well as UV irradiations. Highest photocatalytic degradation efficiency of chromium-nitrogen co-doped zinc oxide could be attributed to the lower rate of recombination of the photo-generated electrons and holes as well as to its lower band gap energy as the result of the co-doping. Photocatalytic degradation is found to follow pseudo first order kinetics. KEY WORDS : Photocatalysts, Precipitation method, Impregnation method, Co-doping, Zinc oxide, Thymol blue Bull. Chem. Soc. Ethiop. 2015 , 29(2), 247-258 DOI: http://dx.doi.org/10.4314/bcse.v29i2.8

Production and Photoelectric Activity of P and Al Co‐Doped ZnO Nanomaterials

Materials that have both conductivity and photocatalytic activity are widely applied in electrical devices and as environmental pollution handles. Based on such requirements, phosphorus and aluminium co-doped conductive zinc oxide nanocrystals (PAZO NCs) with novel visible-light catalytic activities have been mass produced by the combustion method. The PAZO NCs have diameters of 30–100 nm and BET specific surface areas of 15.27–18.99 m2 g–1. These PAZO NCs exhibited novel photocatalytic activity and good conductivity [the powder conductivity was (0.98–1.76) ×10–4 S cm–1], the reason being mainly attributed to the increase in carrier concentration and defects through P and Al co-doping. In addition, we found that the 3PAZO NCs, in which the molar ratio of Zn to P atoms is 100:3, had the best visible-light catalytic efficiency of the PAZO NCs, and the size of PAZO NCs decreased with increasing doping of phosphorus and aluminium. This study is useful as a reference for the mass production of modified ZnO NCs and its applications, such as in environmental management, photocatalysis, and anti-static electricity.

Neutral and warm white light emission in Tb3+/Sm3+ zinc phosphate glasses

A spectroscopy analysis of Tb3+ and Tb3+/Sm3+ doped zinc phosphate glasses based on emission spectra and decay time profiles was performed. The Tb3+ singly doped glass shows a green overall emission with x=0.258 and y=0.429 CIE1931 chromaticity coordinates, upon Tb3+ excitation at 318nm. Under co-excitations of Tb3+ and Sm3+ at 344, 361 and 374nm, the Tb3+/Sm3+ co-doped glasses display neutral and warm white overall emissions with CIE1931 chromaticity coordinates in ranges of x=0.407–0.487 and y=0.437–0.485, color temperature in the range of 2447–4024K and quantum yield up to 12.38%, depending on the excitation wavelength and relative amount of Tb3+ and Sm3+. In all cases, it was observed that the Sm3+ emission is enhanced by the addition of Tb3+, which is correlated with a quenching of the Tb3+ emission as consequence of a non-radiative Tb3+→Sm3+ energy transfer process. The non-radiative nature of the energy transfer process was inferred by the shortening of the Tb3+ emission decay time observed in the Tb3+/Sm3+ co-doped zinc phosphate glasses. An analysis of the Tb3+ emission decay time profiles by the Inokuti–Hirayama model suggests that an interaction electric dipole–dipole into the Tb3+–Sm3+ clusters might dominate in the energy transfer process with efficiency and probability of 0.23–0.25 and 96.22–111.35s−1, respectively.

Effect of oxidation temperature and high magnetic field on the structure and optical properties of Co-doped ZnO prepared by oxidizing Zn/Co bilayer thin films

Co-doped zinc oxide (ZnO) films were fabricated by oxidizing Zn/Co bilayer thin films prepared by vacuum evaporation. The effects of oxidation temperature and high magnetic field on the structure and optical transmittance were investigated. The results show that Co-doped ZnO films in the absence of a magnetic field prefer to grow in a coral dendrite-like morphology. This morphology is inhibited by the Lorentz force of a high magnetic field. Elevating the oxidation temperature to 600 °C from 450 °C can lead to more Zn ions being substituted by Co ions. However, the increase in Co substitution can be inhibited by a high magnetic field. According to X-ray photoemission spectroscopy results, the chemical states of Co are affected by the oxidation temperature and a high magnetic field. Co2+ distributes uniformly in the host ZnO lattice at 450 °C. However, CoO and Co3O4 form at 600 °C without a magnetic field. The obvious energy differences for Co 2p indicate that the Co chemical state changes with the application of a high magnetic field. These results thus show that a high magnetic field can be used to modify the state of Co in ZnO films. Optical transmittance data show that the Co state, O vacancies, and crystallinity have no obvious influence on the transmittance, which is strongly related to the dendrite-like structure.

Effect of small changes in sintering temperature on varistor properties and degradation behavior of V–Mn–Nb–Gd co-doped zinc oxide ceramics

The effect of small changes in sintering temperature on microstructure, electrical properties, dielectric characteristics, and degradation behavior of V–Mn–Nb–Gd co-doped zinc oxide ceramics was investigated. With the increase of sintering temperature, the densities of the sintered pellets decreased from 5.54 to 5.42 g/cm3 and the average grain size increased from 4.1 to 11.7 μm. The breakdown field (E1 mA) decreased noticeably from 7138 to 920 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900 °C exhibited excellent nonohmic properties, which were 66 for the nonohmic coefficient and 77 μA/cm2 for the leakage current density. Concerning stability, the varistors sintered at 900 °C exhibited the strongest accelerated degradation characteristics, with ΔE1 mA =–9.2% for DC accelerated degradation stress of 0.85 E1 mA at 85 °C for 24 h.

Down-shifting by energy transfer in Tb3+/Dy3+ co-doped zinc phosphate glasses

An optical spectroscopy investigation of zinc phosphate glasses activated with Tb3+/Dy3+ ions is carried out through photoluminescence spectra and decay time measurements. The emission color can be adjusted from yellow–green light, with CIE1931 chromaticity coordinates (0.36,0.44), toward the white light region (0.35,0.39) by decreasing the Tb3+ content from 1.0 to 0.1mol% of Tb(PO3)3 upon Dy3+ excitation at 423nm. Such visible region luminescence is generated by 5D4→7F5 and 5D4→7F3 emissions of Tb3+ in addition to 4I15/2→6H15/2, 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 emissions of Dy3+, so that Tb3+ emission is sensitized by Dy3+ through a non-radiative resonant energy transfer. A dominant 5D4→7F5 green emission is observed in detriment of the 5D3→7FJ blue emissions upon 282nm excitation, as well as an extended excitation range (280–500nm), due to multiple Dy3+ and Tb3+ transitions, which might contribute to enhance the spectral response of solar photovoltaic cells by down-shifting of the incident solar spectrum.

Co掺杂闪锌矿ZnO的磁性和光学性质

The band structure,density of state,magnetic and optical properties of Co doped zinc blende Zn O were systematically studied by using the first-principles based on the spin polarized density functional theory. The calculated results show that the ground state of Co doped zinc blende Zn O is antiferromagnetic and shows metal characteristics,while the ferromagnetic state shows the half-metallic characteristics. For the ferromagnetic coupling state,strong spin-orbit coupling appears near the Fermi level and shows no obvious asymmetry for up and down spins,which indicates a significant hybrid effects from Co 3d and O 2p states. The magnetic moments are mainly contributed by unpaired electrons in Co 3d and neighbor O 2p orbital and are correlated to the doped site of Co atoms.In addition,the calculated results of optical properties show that Co doped zinc blende Zn O has a strong absorptive capacity at the visible light,and the absorption peaks have red shift in the high energy region. The theoretical calculated results demonstrate that Co-doped zinc blende Zn O may become excellent magneto-optic materials.

Enhanced tunable color emission in transparent Ag/Mn2+codoped zinc borate glasses for broad band light source

Enhanced ultra-broad band emission has been demonstrated in transparent Ag/Mn2+codoped zinc borate glasses for a broad band light source.

Degradation Characteristics of Pr/Co/Cr/Er Co-doped Zinc Oxide Varistors by Impulse Current Stress

In light of the sure protection function, the most important factors of a varistor are the clamping voltage ratio and degradation characteristics. The degradation characteristics of Pr/Co/Cr/Er co-doped zinc oxide varistors were investigated by impulse currents (0.4~2.1 kA) stress for the specified content of (0.5 and 2.0 mol%). The varistor doped with 2.0 mol% exhibited the best clamp characteristics, with the clamp voltage ratio (K) in the range of K

Effects of post anneal for the INZO films prepared by ultrasonic spray pyrolysis

Indium-nitrogen co-doped zinc oxide thin films (INZO) were prepared on glass substrates in the atmosphere by ultrasonic spray pyrolysis. The aqueous solution of zinc acetate, ammonium acetate and different indium sources: indium (III) chloride and indium (III) nitrate were used as the precursors. After film deposition, different anneal temperature treatment as 350, 450, <TEX>$550^{\circ}C$</TEX> were applied. Electrical properties as concentration and mobility were characterized by Hall measurement. The surface morphology and crystalline quality were characterized by SEM and XRD. With the activation energy analysis for both films, the concentration variation of the films at different heat treatment temperature was realized. Donors correspond to zinc related states dominate the conduction mechanism for these INZO films after <TEX>$550^{\circ}C$</TEX> high temperature heat treatment process.

Yellowish-White Emission from Sol-Gel Mediated Lithium and Aluminium Co-Doped Zinc Oxide Thin Films

Li and Al codoped ZnO (LAZO) thin films have been prepared by sol-gel method. There are two emission bands were observed in the spectra of pure ZnO thin films. One band possessed a sharp peak at round 380 nm locating in the UV range; the other band consists of green luminescence. Yellowish-white emission were observed from the LAZO films, which can be fitted into three bands: a strong yellow emission, a moderate green emission and a weak violet emission centered at 598, 538, and 430 nm, respectively. The luminescence color was seen to be yellowish white due to the recombination for the dominant green and yellow emission.

Effect of Er2O3Content on Nonlinear Properties and Impulse Clamping Characteristics of Pr/Co/Cr/Al Co-doped Zinc Oxide Ceramics

The microstructure, nonlinear properties, and impulse clamping characteristics of Pr/Co/Cr/Al co-doped zinc oxide ceramics were investigated with various contents of Er₂O₃. Increasing Er₂O₃ content increased the density of the sintered pellets from 5.69 to 5.83 g/㎤, and decreased the average grain size from 10.6 to 6.5 μm. With increased Er₂O₃ content, the breakdown field increased from 2318 to 4205 V/cm, and the nonlinear coefficient increased from 19.4 to 40.2. The clamp characteristics were improved with the increase of the content of Er₂O₃. The varistors doped with 2.0 mol% exhibited the best clamp characteristics, in which the clamp voltage ratio was 1.40-1.73 at 1-50 A in an impulse current.