Co-doping Of ZnO Research Articles

Analysis of structural, optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals

Abstract In this paper, the structural, optical and magnetic properties of pure ZnO and Fe/Co co-doped ZnO nanoparticles are presented. Rietveld refinement of XRD pattern revealed the single phase wurtzite structure for prepared samples. FTIR study confirmed the formation of tetrahedral coordination between zinc and oxygen ions. SEM and TEM techniques were used to examine the morphology of samples. The absorption spectra showed the decrease in optical energy band gap with Fe/Co co-doping in ZnO. PL spectra demonstrated five peaks correspond to the ultraviolet region, violet, violet-blue, blue-green and green in the visible region. Emission peak in the UV region is attributed to near band-edge excitonic emission. Other four emission peaks in PL spectra are related to different defect states. M-H curve showed room temperature ferromagnetic (RTFM) behaviour of doped ZnO sample. This paper enhances the understanding of structural, optical and magnetic properties of Fe/Co co-doped ZnO nanocrystals for application in spintronics, solar cells, and ceramics.

Mg and Al co-doping of ZnO thin films: Effect on ultraviolet photoconductivity

Thin films of Zinc Oxide were deposited by the sol-gel technique on glass substrates. The films were doped with Al, Mg or co-doped with both by introduction of appropriate compounds in the solution before dip-coating and annealing in air at 500°C. Energy Dispersive X-Ray Spectroscopy was employed to measure the dopant incorporation. X-ray diffraction studies indicate that Mg doping increases grain size, while Al doping reduces it. Photoluminescence (PL) measurements indicate that undoped and Al-doped films show, along with a broad near band-edge (NBE) peak, additional peaks at longer wavelengths related to various defect states. However Mg doped films show only a sharp NBE peak, which is blue shifted compared to undoped ZnO, and there are no prominent sub band gap luminescence peaks. This is also the case for Mg and Al co-doped ZnO samples, provided the Mg content is low. Photocurrent measurements were carried out using silver contacts using a De source under atmospheric conditions. Undoped and Mg doped ZnO films showed high resistances and low photocurrent levels. With low Al doping, both the dark current and the photocurrent increase significantly, but the films show very long photocurrent transients. With optimized concentration of Mg/Al co-doping in ZnO, the photocurrent increased by ~98 times compared to ZnO films doped only with Mg. Simultaneously, the photocurrent transients became ~44 times faster than ZnO films doped only with Al.

Blue shift in absorption edge and widening of band gap of ZnO by Al doping and Al–N co-doping

Al doped ZnO (ZnO:Al) and Al–N co-doped ZnO (ZnO:Al–N) films were synthesized based on plasma assisted reactive deposition of ZnO matrix and in-situ doping of Al or co-doping of Al and N. Similar with undoped ZnO, the synthesized ZnO:Al and ZnO:Al–N films are hexagonal wurtzite in structure and exhibit high optical transparency in a wide spectral region. Al doping and Al–N co-doping in ZnO result in a significant variation of the optical properties in the ultraviolet (UV) region and an UV extension of the transparent range. Compared with undoped ZnO, the doped films show blue-shifted absorption edge of 320nm and widened band gap of 3.69eV after annealing in H2/N2 mixed gas because of the incorporation of dopants and the improvement in the crystal structure. The ZnO:Al film exhibits declined transparency in the near infrared (IR) region, while the ZnO film co-doped with Al and N preserves high transparency from near UV to medium IR in addition to the UV extension of the transparent range. The annealed ZnO:Al and ZnO:Al–N films show better electrical properties than those of the undoped ZnO film and the as-deposited doped ZnO films.

Studies on visible light photocatalytic and antibacterial activities of nanostructured cobalt doped ZnO thin films prepared by sol–gel spin coating method

Nanostructured cobalt doped ZnO thin films were deposited on glass substrate by sol–gel spin coating technique and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and UV–Vis spectroscopy. The XRD results showed that the thin films were well crystalline with hexagonal wurtzite structure. The results of EDAX and XPS revealed that Co was doped into ZnO structure. FESEM images revealed that the films possess granular morphology without any crack and confirm that Co doping decreases the grain size. UV–Vis transmission spectra show that the substitution of Co in ZnO leads to band gap narrowing. The Co doped ZnO films were found to exhibit improved photocatalytic activity for the degradation of methylene blue dye under visible light in comparison with the undoped ZnO film. The decrease in grain size and extending light absorption towards the visible region by Co doping in ZnO film contribute equally to the improved photocatalytic activity. The bactericidal efficiency of Co doped ZnO films were investigated against a Gram negative (Escherichia coli) and a Gram positive (Staphylococcus aureus) bacteria. The optical density (OD) measurement showed better bactericidal activity at higher level of Co doping in ZnO.

Effects of doping F and transition metal on crystal structure and properties of ZnO thin film

Transition metal (TM=Cu, Ni, Mn, Fe and Co)-doped ZnO:F thin films are deposited on glass substrates by a sol-gel method through using ethanol as solvent. All the samples are checked by using X-ray diffraction (XRD), atomic force microscope (AFM), X-ray photoelectron spectroscope (XPS), photoluminescence, UV spectrophotometer, and vibrating sample magnetometer. The XRD reveals that Cu, Ni, Mn, Fe and Co occupy the Zn sites successfully without changing the wurtzite structure of ZnO at moderate doping concentration, and no evidence of any secondary phases is found. The AFM measurements show that the average values of crystallite surface roughness of the samples are in a range from about 2 to 12.7 nm. The surface of ZnO:F thin film becomes less compact and uniform when ZnO:F thin film is doped with TM ions. The TM ions are indeed substituted at the Zn2+ site into the ZnO lattice as shown in the results obtained by XPS and XRD. Further studies show that most of the ZnO films exhibit preferred (002) orientations, while the best c-axis orientation occurs in Zn0.93Co0.05F0.02O film. However, the crystalline quality and preferential orientation of ZnO film become poor in Zn0.93Mn0.05F0.02O. The optical bandgaps of all the ZnO:F films decrease after doping TM. All the samples show high transmittance values in the visible region. Strong ultraviolet emission and weak blue emission are observed in the photoluminescence spectra measured at room temperature for all the samples. The Zn0.93Mn0.05F0.02O film shows the weakest ultraviolet emission peak and strongest blue emission peak, corresponding to the strongest ferromagnetism; while for the Zn0.96Cu0.02F0.02O film, the strongest ultraviolet emission peak and weakest blue emission peak are observed, accompanied by the weakest ferromagnetism. To determine the optical bandgap (Eg) of TM-doped ZnO:F thin film, we plot the curve of (α hv)2 versus photon energy (hv). It is found that the Eg decreases from 3.16 eV to 3.01 eV with the TM ions doping. We show the variations of saturation magnetization with the Vm O concentration for TM-doped ZnO:F thin films with the different transition metal ions. In the case of Cu-doped ZnO:F thin films, the ZnO sample shows that a weaker magnetism. ZnMnFO film exhibits well-defined hysteresis with a coercive field of 7.28×10-5 emu/g. Further studies reveal that these interesting magnetic properties are correlated with the defect-related model for ferromagnetism. Our results will expand the applications of ZnO:F thin films in visible light emitting diode, photovoltaic devices, photoelectrochromic devices, etc. Meanwhile, extreme cares should be taken to control the codoping of ZnO:F thin films for tuning the magnetization.

Stabilization of Ferromagnetism in Co Codoped ZnO:N

First principle calculations were performed to study room temperature ferromagnetism in N doped ZnO (ZnO:N) using spin density functional theory. Substitution of O by N in ZnO results in spin polarized state exhibiting half metallic ferromagnetic characteristics. Each N dopant introduces magnetic moment of 1.0 μB/supercell, which is from 2p electrons of N but the magnetization energy (ΔE = 14.42 meV) is too small to stabilize ferromagnetism at room temperature. Cobalt (Co) co-doping in ZnO:N is found to enhance ferromagnetism (magnetic moment = 4.24 μB/supercell) with enhanced stability (ΔE = 635 meV) and is driven by hybridization between N 2p and Co 3d states.

N-S共掺ZnO的电子结构和光学性质的第一性原理研究

为了分析纯净ZnO和N元素的掺入对S掺杂ZnO的电子结构和光学性质的影响，基于密度泛函理论采用第一性原理计算方法，我们研究了各种复合体的缺陷形成能、离化能、态密度、导电率、介电函数和吸收系数。结果发现：3N-S共掺ZnO不仅能提高N受主溶解度，而且可以引起浅受主能级。这表明3N-S共掺能够得到高质量稳定p型ZnO。同时，随着N原子的增加，体系的离化能迅速降低，而体系的导电率增强。另外，通过对介电函数和吸收系数的计算，结果表明3N-S共掺ZnO在低能区有非常奇特的特性。希望不久我们的理论结果能够为实验提供理论依据。 To analyze the electronic structures and optical properties of pure-ZnO and N-S codoped ZnO, the defect formation and ionization energy, density of states, conductivity, dielectric constant and adsorption coefficient of varies complexes were calculated by the first-principles calculation methods based on Density Functional Theory (DFT). It is found that 3N-S codoping in ZnO not only enhances N acceptor solubility, but also leads to shallower acceptor energy, demonstrating that 3N-S codoping can obtain a high-quality and more stable p-type ZnO. Furthermore, as the incorporation of N atoms is increasing, the ionization energies of the complexes are sharply decreasing, and the conductivity of the system is enhanced. In addition, the calculation of the dielectric functions and adsorption spectrum shows that 3N-S codoped ZnO has interesting characteristic in the low-energy region. We expect that this theory study might be helpful for the experimental results.

Study of Structural and Optoelectronic Properties of ZnO Codoped with Ca and Mg

ZnO codoped with Ca and Mg in various proportions was prepared by a chemical method and annealed at 600 C. The structural and optical properties of these oxide samples were systematically studied by XRD, SEM, EDS, and PL spectrometer. XRD pattern shows a hexagonal wurtzite structure. The size of particle as shown by XRD machine and calculated by Scherer’s formula is found in the nano range. The formation of particles showed that they were polycrystalline. Due to larger ionic and covalent radii of Ca than those of Zinc, a lattice deformation occurs with the development of strain field. New phases were observed in XRD pattern of few samples ZnO-2.2 and ZnO-2.4. SEM micrograph shows the formation of nanoparticles. EDS study confirms the codoping of ZnO with Ca and Mg. Optical properties like photoluminescence emission showed a blue shift in peak wavelength. General conductivity and photoconductivity were found high in samples containing certain proportion of Ca and Mg in comparison with pure ZnO.

Observation of bandgap narrowing effect and photoluminescence emission characteristics of chemically synthesized Co doped ZnO nanosheets

We have reported the effect of Co doping on structural and optical properties of ZnO nanosheets and demonstrated bandgap narrowing effect, thus making it suitable for visible light absorption. The undoped and Co doped (0.5–2.5 %) ZnO nanosheets have been synthesized by a chemical method at 65 °C. The nanostructures of the samples have been studied by using electron microscopes and X-ray diffraction (XRD). UV–Visible spectrophotometric technique has been used to find the bandgap of the samples and shift of bandgap energy has been found to vary exponentially with Co doping concentration. The measured photoluminescence (PL) emission spectra of the samples have shown the presence of a near-band-edge emission band and a red shift from 383 to 387 nm due to Co doping. A visible PL emission band appears at ~603 nm in the undoped sample and it is quenched by a considerable amount after Co doping in ZnO. The calculated value of strain present in the samples and square of the volume of unit cell, calculated from XRD data, are found to vary linearly with the shift of band gap energy. The synthesized Co doped ZnO nanosheets may find significant application in designing solar cell.

First-principles calculation on p-type conduction of (Sb, N) codoping in ZnO

Based on first-principles calculations, (Sb, N) codoped ZnO are investigated. We find that SbZn–4NO have lower formation energy and can form p-type conduction with smaller hole effective mass. In comparation to monodoping of Sb, SbZn–4NO complex can form better p-type conductivity than SbZn–2VZn, which may be strongly compensated by SbZn defect and result in a decrease of p-type conduction. So we inferred that (Sb, N) codoping in ZnO under O-poor condition should be a realizable candidate of p-type conduction.

Influence of Co doping on the structural, optical and magnetic properties of ZnO nanocrystals

A systematic investigation on the synthesis, characterization, optical and magnetic properties of Co doped ZnO nanocrystals have been reported. Nanocrystals of Zn1−xCoxO (where x = 0.05 and 0.10) were synthesized using the Sol–gel technique. Structural, optical and magnetic properties of the samples were investigated by X-ray diffraction (XRD), UV–VIS–NIR spectroscopy, Raman spectroscopy and SQUID magnetometer. Energy dispersive X-ray, Scanning electron microscopic, XRD and Raman measurements showed that the Co ions were successfully doped at the Zn site in the wurtzite type ZnO lattice. An appreciable blue shift in the absorption spectrum was observed, which indicates that the Co doping in ZnO leads to systematic increase in the band-gap with dopant concentration. Magnetization studies showed that the Co doped ZnO nanocrystals display room temperature ferromagnetism and the ferromagnetic ordering strengthens with the Co concentration.

Thermo-mechanical behaviour of alkali free bioactive glass-ceramics co-doped with strontium and zinc

We report on the influence of SrO and ZnO co-doping on thermo-mechanical behaviour of alkali free bioactive glass-ceramics in system: (mol%) (36.07−x) CaO–x SrO–(19.24−y) MgO–y ZnO–5.61 P2O5–38.49 SiO2–0.59 CaF2 (x=2–10, y=2–10). Hot-stage microscopy and differential thermal analysis revealed that densification of all the glass powders occurs before the onset of crystallization, resulting in well sintered and mechanically strong glasses/glass-ceramics after heat treating for 1h under non-isothermal conditions at 800, 850 and 900°C. The crystalline phase assemblage in the sintered compacts included diopside (CaMgSi2O6) and fluorapatite [Ca5(PO4)3F] with partial replacement of Ca for Sr with increasing strontium contents. The effect of heat treatment temperature on mechanical reliability was assessed by Weibull statistical analysis applied to the flexural strength data. The results obtained revealed that a better balance of properties was achieved for the samples sintered at 850°C. These results provide an insight into the choice of final material/experimental conditions for the development of three-dimensional porous scaffolds for bone tissue engineering.

Room Temperature Ferromagnetism in PLD Grown Zn1-xLixO1-yNy Thin Films

Zn1-xLixO1-yNy (ZnO:(N,Li)) thin films grown by Pulsed Laser Deposition (PLD) technique are found to exhibit intrinsic ferromagnetic behavior at room temperature (RT). XRD reveals that the grown Zn1-xLixO1-yNy thin films (x = 0.05, y = 0.08) are single phase and preferred oriented along c-axis. In contrast to pure ZnO thin films, ZnO thin films doped with non-magnetic nitrogen (ZnO:N) result in good M-H hysteresis loop at RT. Co-doping of ZnO:N with Li is found to enhance the saturation magnetization (Ms) appreciably. The room temperature ferromagnetic behavior and semiconducting property of Zn1-xLixO1-yNy thin film could be promising for spin injection based functional devices.

Giant stability of substituent Co chains in ZnO:Co dilute magnetic oxides

Chemical and magnetic structures of substituent Co ions in ZnO:Co dilute magnetic oxides are investigated by using first-principles density functional calculations of isolated Co, clustered Co-O-Con (n>0) and chained -Co-O-Co-O-. It demonstrates that the substitutional Co ions in ZnO tend to form -Co-O-Co-O- chains or Co-O-Con clusters rather than stay isolated. The most stable structure was identified to be antiferromagnetic -Co-O-Co-O- chains via O on ab plane rather than Co-O-Con clusters. Furthermore, substituent Cu codoping in ZnO is disclosed to suppress the Co's tendency towards chain-like structures or clusters, thus enhancing its homogeneous distribution.

The band gap broadening and absorption spectrum of wurtzite Zn1−xCoxO from first-principles calculations

The band structures, density of states and absorption spectra of un-doped and Co-doped ZnO supercells of Zn1−xCoxO (x=0.0417, 0.0625 and 0.1250) have been investigated using first-principles plate-wave uitrasoft pseudopotential method based on the density functional theory. The calculated results showed that the band gaps are broadened by Co doping in ZnO, which is because of the valence band undergoes a greater shift toward the low-energy region than the conduction band lead to. Moreover, the optical absorption edge exhibits a blue-shift, and the heavier the doping concentration is, the more significant the blue-shift will be, which is in agreement with the experimental results.

A study of structural, optical and magnetic properties of Cr, Ce co-doping in ZnO diluted magnetic semiconductors

We present the structural, optical and magnetic properties of pure ZnO, Zn0.97Cr0.03O and Zn0.96Cr0.03Ce0.01O samples, the samples were synthesized by sol–gel method. The microstructures, optical and magnetic properties of samples were investigated by X-ray diffraction (XRD), transmission electron microscope , X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), Raman spectroscopy and vibrating sample magnetometer. XRD and XPS data confirmed the formation of a single phase wurtzite type ZnO structure for all the samples. PL measurements revealed that all the three samples had an UV emission and a defect emission, and the Ce ions doping induced a red shift in the UV emission and an increase in the defect emission. Zn0.97Cr0.03O and Zn0.96Cr0.03Ce0.01O samples showed the obvious hysteresis loops at room temperature and the saturation magnetization (Ms) increases with incorporating of Ce.

Enhancement of 1.54 μm emission in Er:LiNbO3 crystal by codoping with Zn2+ ions

The enhanced intensity and lengthened lifetime of 1.54 μm emission were observed for Er:LiNbO3 crystal codoped with Zn2+ ions. The ZnO codoping led to the reduction of the green upconversion emission in Er:LiNbO3 crystals. The decay trace of the 4S3/2→4I15/2 was obviously nonexponential for Er:LiNbO3 codoped with 0 and 3 mol.% ZnO, but became exponential for one codoped with 6 mol.% ZnO. The OH− absorption spectra showed after codoping with Zn2+ ions, the OH− absorption peaking position shifted from ∼3495 to 3484 cm−1, and the absorption cross section decreased. These spectroscopic characteristics suggested that the improvement of 1.54 μm emission was attributed to the reduction of Er3+ cluster sites.

Effect of Co substitution on the structural and optical properties of ZnO nanoparticles synthesized by sol–gel route

Co doped ZnO nanoparticles were synthesized by sol–gel method and characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDAX), UV–Visible absorption spectroscopy and Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the formation of single phase structure of all samples which was further supported by FTIR data. With the increase in Co concentration from 0% to 5%, crystallite size was observed to vary from 27.1 to 21.3 nm. It suggests the prevention of crystal growth as a result of Co doping in ZnO. It was also evident from the absorption spectra that the absorbance tends to increase with the increase in dopant concentration. Optical band gap was found to increase slightly with the increase in Co content, confirming the size reduction as a result of Co doping.

Low-Temperature Sintering of ZnO and B<sub>2</sub>O<sub>3</sub> Co-Doped (K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub> Lead-Free Piezoelectric Ceramics

Lead-free K0.5Na0.5NbO3-xwt% (0.4ZnO-0.6B2O3) ceramics were synthesized by conventional ceramics process. The co-doping of ZnO and B2O3can decrease the sintering temperature of K0.5Na0.5NbO3ceramics to 1000°C, and the samples show high relative density around 96%. X-ray diffraction (XRD) reveals that Co-doping of ZnO and B2O3induces lattice distortion. Liquid phase is observed by scanning electron microscopy (SEM), which is resulted from the addition of ZnO and B2O3. The ceramics show better piezoelectric and dielectric properties with planar electromechanical coupling factorkp= 40.7%, piezoelectric constantd33=117pC/N, dielectric constantεT33/ε0=318.6, and loss tangenttanδ=0.034.

Co-doping effect of Zn and Sb in SnO 2: Valence stabilization of Sb and expanded solubility limit

In this study, the co-doping effect of ZnO and Sb 2O 5 on the solubility limit in SnO 2 was investigated. When ZnO was added to SnO 2, its solubility limit was around 3 at%, while that of Sb 2O 5 could not be evaluated due to the severe evaporation of Sb 2O 5 during sintering. For the co-doping of ZnO and Sb 2O 5, the ZnSb 2O 6 phase was used for the source of Zn and Sb dopants to prevent the evaporation of Sb 2O 5. When ZnO and Sb 2O 5 were co-doped by ZnSb 2O 6, the solubility limit expanded to 60 at%. XPS analysis of the Sb revealed that Sb 5+ is stable when Zn is co-doped. The extended solubility limit is explained by electrostatic and strain energy minimization in the lattice.