Structural,optical and magnetic properties of cobalt-doped CdSe nanoparticles

Pure and Co-doped CdSe nanoparticles have been synthesized by hydrothermal technique. The synthesized nanoparticles have been characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Visible), photoluminescence spectroscopy (PL), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID), at room temperature. From XRD analysis, pure and cobalt-doped CdSe nanoparticles have been found to be polycrystalline in nature and possess zinc blende phase having cubic structure. In addition to this, some peaks related to secondary phase or impurities such as cobalt diselenide (CoSe₂) have also been observed. The calculated average crystallite size of the nanoparticles lies in the range, 3–21 nm, which is consistent with the results obtained from TEM analysis. The decrease in average crystallite size and blue shift in the band gap has been observed with Co-doping into the host CdSe nanoparticles. The magnetic analysis shows the ferromagnetic behaviour up to 10% of Co-doping concentration. The increase of Co content beyond 10% doping concentration leads to antiferromagnetic interactions between the Co ions, which suppress the ferromagnetism.     

Variation in structural,optical and magnetic properties of Zn1−xCrxO (x = 0.0, 0.10, 0.15, and 0.20) nanoparticles: Role of dopant concentration on non-saturation of magnetization

Cr-doped ZnO, i.e. Zn_1−xCr_xO (x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by sol–gel route. The structural and morphological properties of these nanoparticles were investigated by high resolution transmission electron microscope (HRTEM). The average particle size of Zn_1−xCr_xO nanoparticles decreases from 75 to 40 nm with the increase in x from 0.00 to 0.20. The rings observed in selected area diffraction pattern revealed that up to x = 0.10 these nanoparticles have single phase ZnO. However, a secondary spinel phase of ZnCr₂O₄ was observed for higher Cr doping (x ≥ 0.15). The optical band gap calculated using UV–visible absorption was decreased from 3.27 to 2.27 eV with the increase in Cr-doping from 0.00 to 0.20 in ZnO nanoparticles. The undoped ZnO (Zn_1−xCr_xO; x = 0.00) nanoparticles did not show any hysteresis loop at room temperature, however, clear loops were obtained for x = 0.05–0.20. Additionally, magnetization (M) vs. applied magnetic field (H) loops for lower Cr-concentration (x = 0.05) saturate at 5 kOe, and while those with higher Cr concentration (x > 0.05) do not show saturation even at 10 kOe. This may be attributed to increase in the defects at higher Cr-doping into ZnO. The value of saturation magnetization was found to decrease from 4.24 emu g⁻¹ to 1.96 emu g⁻¹ with the increase in Cr doping from x = 0.05 to 0.20 in ZnO and may be due to the secondary ZnCr₂O₄ phase.     

Chemical,morphological, structural,optical, and magnetic properties of Zn<Subscript>1−x</Subscript>Nd<Subscript>x</Subscript>O nanoparticles

In the present investigation, we made an endeavor to fabricate the ZnO nanoparticles and achieved the tunable properties with Nd doping. The Nd-doped ZnO nanoparticles were characterized via X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) studies that confirmed the successful doping of Nd ions in the ZnO crystal lattice without amending its hexagonal phase. The particle morphology revealed nearly spherical particles with uniform size distribution. The band gap of these samples was determined using diffuse-reflectance spectra (DRS) and was found to vary from 3.17 to 3.21 eV with increasing Nd concentration. A broad and intense emission band at 1083 nm for Nd doped ZnO nanoparticles is observed and is assigned to corresponding emission transition ⁴F_3/2?→?⁴I_11/2 of Nd³⁺ ions. Furthermore, the magnetic studies indicate that the Nd doping altered the magnetic behavior of nanocrystalline ZnO particles from diamagnetic to ferromagnetic at 300 K and that the magnetization of these samples decreased with increasing Nd concentration. The tunable optical band gap as well as room-temperature ferromagnetism of these samples may find applications in both optoelectronics and spintronics.     

Effect of Co-doping on the performance of nanosheet-like ZnO ethanol gas sensor

In this paper, a hydrothermal method was applied to synthesize the nanosheet-like pure ZnO and 0.5%, 1 and 3% Co-doped ZnO (Co-ZnO). The pristine and Co-doped ZnO flower-like particles were assembled by porous nanosheets, with the uniform diameter about 18 μm. The N₂-BET test found that Co doping significantly increased the specific surface area of the material which was conducive to gas diffusion and adsorption. HRTEM presented that 1% Co-ZnO nanosheets were composed of coral-like nanoparticles. The lattice distances 0.259 nm and 0.276 nm correspond to (002) and (100) crystal plane of ZnO. The gas sensing properties reveal that the 1% Co-doped ZnO present an outstanding enhanced sensitive performance comparing with pure ZnO to ethanol. To 100 ppm target gas, the response increased from 103 to 279.8 and the optimal operating temperature decreased from 369 to 348 °C, and the recovery time decreased from 40 to 18 s. The increased surface carrier concentration which promoted oxygen adsorption by Co was considered to be the key factor to improve the performance.

     

Structural, optical and photoluminescence studies of heavily Mn-doped ZnO nanoparticles annealed under Ar atmosphere

Undoped and heavily Mn-doped with ZnO nanoparticles (Zn_1?xMn_xO, x?=?0.0, 0.05, 0.1 and 0.2) annealed under Ar atmosphere have been synthesized by a sol–gel method. The structural properties and optical absorption of the prepared samples have been examined by powder X-ray diffraction, energy dispersive X-ray analysis, Fourier transform infrared (FTIR) spectroscopy and UV–visible spectrophotometer. Hexagonal wurtzite structure of the samples is confirmed by the XRD spectra. The average crystalline size of the Zn_1?xMn_xO nanoparticles has been calculated from X-ray line broadening and is decreased from 35.73 to 18.24?nm with increase in Mn concentrations from 0.0 to 0.2. The increase in lattice parameters indicates the substitution of Mn in ZnO lattice. SEM and TEM photographs indicated that the grain size of undoped ZnO is bigger than the Mn-doped ZnO which is due to the limitations of grain growth upon Mn doping. The presence of functional groups and the chemical bonding due to Mn doping is confirmed by FTIR spectra. PL spectra of the Zn_1?xMn_xO system showed that the shift in near band edge emission at 390?nm and a blue band emission at 450–490?nm which confirms the substitution of Mn.     

Growth of Co-Doped ZnO Ferromagnetic Nanoparticles by Sol-Gel Method

Co-doped ZnO nanoparticles have been synthesized by a simple sol-gel route using zinc acetate dihydrate and cobalt(II) acetate tetrahydrate as precursors. The X- ray diffraction and high-resolution transmission electron microscopy show that Co doping has a significant effect on the crystalline nature of ZnO nanoparticles. Thermal analysis indicates that the Co-doped ZnO system is well stable above 300 ^°C. Raman spectroscopy shows the prominent modes at 331, 434, and 579 cm^?1 with 0–2 % doping, whereas additional modes at 490, 525, and 715 cm^?1 corresponding to secondary phases have also been observed for 3–5 % of Co doping in ZnO nanoparticles. The M–H and M–T curves confirmed the ferromagnetic nature of Co-doped ZnO nanoparticles at room temperature.     

Enhanced photocatalytic activity of Fe-doped ZnO nanoparticles synthesized via a two-step sol–gel method

A series of Zn_1–x Fe _x O (x = 0, 1, 2, 3, 4 %) powders via a two-step sol–gel method in open system were successfully fabricated. Influence of Fe doping concentration on the structure, morphology, optical properties and photo catalysis properties were investigated by means of X-ray diffraction, scanning electron microscopy, UV–Vis spectrophotometer and photochemical reaction instrument. The results showed that the ZnO powders were hexagonal wurtzite structures and their crystalline sizes and particle diameters decreased with the increase of Fe doping concentration. An increase of visible light absorption value and a decrease in band gap from 3.219 to 3.167 eV were found with the increase of Fe doping concentration, which enable the sample harvest more photons to excite the electron from the valence. Enhanced visible light induced photocatalytic activity has been found in Fe doped ZnO and the ultraviolet light induced photocatalytic properties of the Fe-doped ZnO have been improved greatly compared with undoped ZnO and commercially available TiO₂ (P25). The photocatalytic activities were not significantly affected by the particle size, and the best Fe doping concentration is 1 %.     

Synthesis and Characterization of Fe-Doped CdSe Nanoparticles as Dilute Magnetic Semiconductor

Cd_1?x Fe _x Se (0??x??0.1) nanoparticles were synthesized by hydrothermal method. The solubility limit of Fe in CdSe nanoparticles was found to be less than 6?% as obtained from X-ray diffraction (XRD) study. With the increase in doping concentration at and above it, secondary phase of FeSe₂ starts appearing. The presence of Cd, Se, and Fe has been confirmed by energy dispersive X-ray spectroscopy (EDS). The increase in band gap value has been confirmed by UV-visible spectra and the variation in emission intensity of photoluminescence (PL) measurements further indicates the incorporation of Fe in CdSe nanoparticles. Transmission electron microscopy (TEM) reveals the spherical nature of synthesized nanoparticles, and the particle size decreases with increasing Fe doping concentration. Fourier transform Infrared spectra (FTIR) confirm the capping of sodium dodecyl sulfate (SDS) surfactant on pure and Fe-doped CdSe nanoparticles. The synthesized nanoparticles show room-temperature ferromagnetic behavior, and the saturation magnetization value was found to increase with Fe doping concentration.     

Preparation, Growth, and Magnetic Properties of Co-doped Yb2O3 Nanoparticles and Thin Films by the Sol–Gel Process

In this study, the preparation, growth, structure and magnetic properties of Co-doped Yb₂O₃ (with the Co concentration of x=0.2) nanoparticles and thin films are studied. Precursor solutions were prepared by using the sol?Cgel synthesis process to produce nanoparticles and thin films. Co-doped Yb₂O₃ thin films with different thickness were produced on Si(100) substrate using the sol?Cgel dip coating procedure. The particle size and the crystal structure of nanoparticles were ascertained by X-ray diffraction and Scanning Electron Microscope. The surface morphologies and the microstructure of all samples were investigated by means of the Scanning Electron Microscope and the X-ray diffraction. A Quantum Design PPMS was used for magnetic measurements. Surface morphologies of Co-doped Yb₂O₃ thin films were found to be dense, without porosity, uniform, and devoid of cracks and pinholes. The grain size and thin-film thickness of Co-doped Yb₂O₃ were determined to be approximately 50?nm and 84?nm, respectively.     

Synthesis,structural and optical characterization of Ni-doped ZnO nanoparticles

Nanocrystalline Zn_1−x Ni _x O (x = 0.00, 0.02, 0.04, 0.06, 0.08) powders were synthesized by a simple sol–gel autocombustion method using metal nitrates of zinc, nickel and glycine. Structural and optical properties of the Ni-doped ZnO samples annealed at 800 °C are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis using X-rays (EDAX), UV–visible spectroscopy and photoluminescence (PL). X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a hexagonal wurtzite structure and secondary phase (NiO) was observed with the sensitivity of XRD measurement with the increasing nickel concentration (x ≥ 0.04). The lattice constants of Ni-doped ZnO nanoparticles increase slightly when Ni²⁺ is doped into ZnO lattice. The optical absorption band edge of the nickel doped samples was observed above 387 nm (3.20 eV) along with well-defined absorbance peaks at around 439 (2.82 eV), 615(2.01 eV) and 655 nm (1.89 eV). PL measurements of Ni-doped samples illustrated the strong UV emission band at ~3.02 eV, weak blue emission bands at 2.82 and 2.75 eV, and a strong green emission band at 2.26 eV. The observed red shift in the band gap from UV–visible analysis and near band edge UV emission with Ni doping may be considered to be related to the incorporation of Ni ions into the Zn site of the ZnO lattice.     

Optical, magnetic and structural characterization of Zn1 − x Co x O nanoparticles synthesized by solvothermal method

Nanoparticles of Co-doped ZnO with 3·8, 7·2 and 11·5 wt% were synthesized by solvothermal method through oxalate precursor route. X-ray diffraction studies showed the formation of hexagonal ZnO structure for x?= 0·038, however, secondary phase of Co₃O₄ arises on increasing the Co content up to 11·5%. Transmission electron microscopic studies showed that particles are in the nano-metric regime and the grain size decreases on increasing the Co concentration. Optical reflectance measurements showed an energy bandgap, which decreases on increasing Co concentration. Specific surface area of these nanoparticles was found to be very high and comes out to be 97·6, 112·1 and 603·8 m²g^???1, respectively. All the solid solutions showed paramagnetism with weak antiferromagnetic interactions. It is seen that the antiferromagnetic interaction increases on increasing Co concentration.     

Influence of Co-doping on the structural, optical and magnetic properties of ZnO nanoparticles synthesized using auto-combustion method

In the present work, we have interested to understand the influence of cobalt doping on the various properties of ZnO nanoparticles, a series of samples were successfully synthesized using sol–gel auto-combustion method. The effects of Co doping on the structural and optical properties of ZnO:Co nanoparticles were investigated using X-ray diffraction (XRD), scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy and vibrating sample magnetometer (VSM). With the sensitivity of the XRD instrument, the structural analyses on the undoped and Co-doped ZnO samples reveal the formation of polycrystalline hexagonal-wurtzite structure without any secondary phase. FTIR spectra confirm the formation of wurtzite structure of ZnO in the samples. The optical absorption spectra showed a red shift in the near band edge which indicates that Co²⁺ successfully incorporated into the Zn²⁺ lattice sites. The room temperature PL measurements show a strong UV emission centered at 392 nm (3.16 eV), ascribed to the near-band-edge emissions of ZnO and defect related emissions at 411 nm (violet luminescence), 449 nm (blue luminescence) and 627 nm (orange-red luminescence), respectively. Magnetic study using VSM reveals that all the samples are found to exhibit room temperature ferromagnetism.     

Temperature dependence of conduction mechanism of ZnO and Co-doped ZnO thin films

ZnO and Co-doped ZnO thin films have been deposited on the sapphire substrate by ultrasonic assisted chemical vapor deposition technique. The films were annealed in vacuum at 450 °C. All the films were highly c-axis orientated and contained no impurity phase. The temperature dependence of the electrical conductivity has been measured in order to identify the dominant conduction mechanism. In the higher temperature region the dominance of thermally activated band conduction was observed whereas in the low temperature region the hopping conduction was found to dominate. The hopping conduction mechanism in the lower temperature range in the film was Mott's Variable Range Hopping and not the Nearest Neighbor Hopping. The temperature region, where hopping conduction was dominant found to increase by Co doping in ZnO film. The localization length was found to be larger in the Co-doped ZnO film.     

Effects of Mn dopant on tuning carrier concentration in Mn doped ZnO nanoparticles synthesized by co-precipitation technique

Zn_1???x Mn _x O (x?=?0.002–0.01) nanoparticles were synthesized by co-precipitation method. The detailed crystal structure and compositional characterizations were characterized by the XRD patterns, Raman spectra, XPS, HRTEM and SEM. the XRD and XPS results show the Mn²⁺ ions are substitute for Zn²⁺ ions in the ZnO matrix. In the Raman spectra, the E₂(high) peak shifts to lower frequency and the higher intensity of A₁(LO) peak appears in the sample with increasing doping concentrations of Mn, indicating a higher concentration of donor defects are introduced in ZnO nanoparticles. Then, the carrier concentration induced by oxygen vacancies are analyzed from the optical absorption spectra. By analyzing the O1s XPS spectrum by Lorentz fitting and PL spectra by Gaussian fitting, the oxygen vacancy concentration increases with Mn doping concentration. The present results suggest that the doped Mn²⁺ ions play a significant role on enhancing the carrier concentration of ZnO materials.     

Structure and optical properties of MgxZn1−xO nanoparticles prepared by sol–gel method

Mg_xZn_1−xO particles were synthesized by the sol–gel technique using acetate of zinc and magnesium in a homogeneous aqueous reaction medium. XRD showed that the particles possessed a polycrystalline hexagonal wurtzite structure. The transmission spectroscopes of ZnO, Mg_xZn_1−xO and the mixture of ZnO with MgO were investigated. It was found that the band gap of zinc oxide was increased from 3.32 to 3.65 eV by doping 15% magnesium oxide. TEM picture revealed that Mg_xZn_1−xO particle was about 30 nm with a narrow size distribution. The conductivity and the dielectric properties of the powders have also been improved by Mg doping.     

Transparent and electrical properties of Ga-doped Zn1−x Cd x O films post-annealed in vacuum and nitrogen

(Cd,Ga)-codoped ZnO films were prepared by sol–gel method. The codoping films retained wurtzite structure of ZnO, and showed preferential c-axis orientation. The transparent and electrical properties of the films post-annealed in vacuum and nitrogen were investigated. The transmittances of the films were degraded to 60–70 % by vacuum annealing, but enhanced to 80–90 % by nitrogen annealing. The carrier concentration increased, while resistivity decreased with the narrowing band gap, i.e. Cd doping could increase the conductivity of the Ga-doped Zn_1?x Cd _x O films by narrowing their band gap. The band gap modification was attributed to both Cd doping (majority) and Burstein–Moss effect (minority). The resistivity of nitrogen annealing films was one order higher than that of vacuum annealing films. It seemed that the transmittance and conductivity was irreconcilable, while the trade-off between them might be modulated by different post-annealing ambient.     

Preparation and photoluminescence of surface N-doped ZnO nanocrystal

ZnO nanoparticles doped with nitrogen on surface were prepared by calcinating pure ZnO nanoparticles at 550 and 600 °C in NH₃ atmosphere. Uniform N-doped ZnO nanocrystal was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and XPS. A Strong violet photoluminescence (PL) at 400nm was observed at room temperature when excited with 300 nm light, and the emission peak increases with the increase of nitrogen atoms concentration. The violet PL originated from the electron transition from shallow donor levels of oxygen vacancies and doping nitrogen atoms to the top of valence band level.     

Structural,optical and intrinsic defects induced magnetic properties of the ZnO:Fe nanoparticles

In this present work, the Fe ions doping effect on the structural, vibrational, optical and magnetic behavior of ZnO nanoparticles are reported. The Zn_1?xFe_xO (with 0 ≤ x ≤ 0.05) samples were prepared by co-precipitation method. The presence of single crystalline phase identified as the Wurtizite structure was determined by X-ray diffraction measurement in all the samples. Additionally, a small peak shift and suppression of peak intensity have been found on Fe doping increases in ZnO matrix. The Zn_1?xFe_xO samples are further characterized by Raman spectra, photoluminescence, UV–DRS, FTIR, electron paramagnetic resonance spectroscopic measurements. The structural change and presence of intrinsic defects were confirmed by Raman spectra and PL analysis. Also, the optical properties arise from by the incorporation of the dopant ions and their effect on the bandgap subsequently. The magnetic properties of the prepared samples are measured using VSM. The observed room temperature ferromagnetism and the nonmonotonic variation in the magnetic properties are discussed based on the presence of intrinsic defects and grain boundary network.     

Synthesis and study of the structure,magnetic, optical and methane gas sensing properties of cobalt doped zinc oxide microstructures

Undoped and Cobalt (Co) doped zinc oxide (ZnO & CZx) nanoparticles were synthesized by Solvothermal method. The samples were studied by X-Ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), UV–Vis spectroscopy and Scanning and Transmission Electron Microscopy (SEM & TEM). Moreover the gas sensing properties of the nanoparticles for methane gas took place. Purity of the samples and Co concentration was investigated by EDS and ICP spectroscopy respectively. XRD results described the hexagonal wurtzite structure for all the samples in which crystallinity and the crystallites size decreased with increase of Co doping level. Using UV–Vis spectroscopy the band gap energy was evaluated and redshift of band gap energy was observed by increasing of Co concentration. SEM images demonstrated that nanoparticles were agglomerated with increase of Co doping level. TEM images revealed the nanoparticles size in the range 11–44 nm. Methane sensing properties was enhanced after Co doping of the ZnO nanoparticles for Co concentration up to 4%.     

Effect of Co doping on morphology, optical and magnetic properties of ZnO 1-D nanostructures

One-dimensional Co doped ZnO nanostructures have been successfully synthesized by a wet chemical technique. X-rays diffraction results reveal that with Co doping ZnO retained its wurtzite structure, but lattice constants are slightly decreased. SEM results demonstrate that Co doping changes morphology of ZnO nanostructures from nanowires to nanorods. It has been confirmed through HRTEM results that Co dopant cannot change preferred growth orientation of ZnO, although it remarkably influenced the grain size and morphology. The Co dopant is found to be uniformly distributed over various parts of single nanorod and settles at 2+ chemical oxidation state without forming any secondary phases. In response to Co doping, near band edge peak in UV region is red shifted and VL band peak intensity is remarkably enhanced. It is also found that Co doping induces large amount of defects in ZnO band structure. Furthermore, the doped nanorods exhibit ferromagnetic behavior at room temperature, which is attributed to the presence of abundant amount of defects and oxygen vacancies. The tunned band gap and ferromagnetic behavior at room temperature with high M _s and H _c values make them potential for spintronics applications.