Size-dependent magnetic and dielectric properties of Tb-doped BiFeO3 nanoparticles

Pure and Tb-doped BiFeO₃ nanoparticles have been prepared by sol–gel method. The nanoparticles of different size have been obtained by the calcination of synthesized nanoparticles at different temperatures. The effects of Tb doping and size of nanoparticles on the crystal structure, magnetic and electrical properties have been studied. The partial substitution of Tb ions results in a change from rhombohedral (x = 0) to orthorhombic (x = 0.15) structure. The average crystallite size varies from 14 to 40 nm. The synthesized nanoparticles possess ferromagnetic behavior. The saturation magnetization is high for the Tb-doped BiFeO₃ nanoparticles calcined at 450 °C, and it decrease with the increase of size. The dielectric constant and loss improve with Tb doping and size. The relaxation behavior of dielectric loss is of Debye type. The dielectric loss peaks shift to the lower frequencies with increase in the size of Tb-doped BiFeO₃ nanoparticles.     

Effect of Tb<Superscript>3+</Superscript> ion substitution on structural,optical and magnetic properties of CdS nanoparticles

Cd_1?xTb_xS (x?=?0.00, 0.05, 0.10, 0.15) nanoparticles were synthesized by hydrothermal technique. The effect of Tb-doping on structural, optical and magnetic properties were studied. The X-ray diffraction (XRD) confirmed wurtzite phase without any impurity. HR-TEM micrographs revealed the particle size of ~?18 nm with spherical morphology. Band gap calculated from UV–Visible absorption spectra showed an initial decrease from 2.49 eV (x?=?0) to 2.45 eV (x?=?0.10). Further, increasing Tb-doping to x?=?0.15 band gap increased to 2.54 eV. Photoluminescence emission spectra showed peaks at 430 and 490 nm for x?=?0 and 0.05 which corresponds to blue emission. Further increase in Tb doping, peaks found to be quenched. Peak at 530 nm is due to green emission and shifted to higher wavelength with Tb-doping. Magnetic analysis confirmed ferromagnetism in both undoped and Tb-doped nanoparticles. Saturation magnetization found to decrease upto x?=?0.10 and increased for x?=?0.15.     

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.     

Optical and magnetic properties of Cu-doped ZnO nanoparticles

Cu-doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Cu:Zn atomic ratio from 0 to 5 %. The synthesis process was based on the hydrolysis of zinc acetate dehydrate and copper acetate tetrahydrate heated under reflux to 65 °C using methanol as a solvent. X-ray diffraction (XRD) analysis reveals that the Cu-doped ZnO crystallize in a wurtzite structure with a change of crystal size from 12 nm for undoped ZnO to 5 nm for Cu-doped ZnO. These nano size crystallites of Cu doped ZnO self-organized into microspheres. The XRD patterns, Scanning electron microscopy and transmission electron microscopy micrographs of doping of Cu in ZnO confirmed the formation of microspheres and indicated that the Cu²⁺ is successfully substituted into the ZnO host structure of the Zn²⁺ site. Cu doping shifts the absorption onset to blue from 373 to 350 nm, indicating an increase in the band gap from 3.33 to 3.55 eV. A relative increase in the intensity of the deep trap emission of Cu-doped ZnO is observed when increasing the concentration of Cu. Magnetic measurements indicate that Cu-doped ZnO samples are ferromagnetic at room temperature except pure ZnO.     

Synthesis, structural and optical properties of Ni-doped ZnO micro-spheres

Ni doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Ni:Zn atomic ratio from 0 to 5 %. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and nickel acetate tetrahydrate followed by heat treatment at 65 °C under refluxing using methanol as a solvent. X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a wurtzite structure with crystal size of 4–11 nm. These nanocrystals self-aggregated themselves into hollow spheres of size of 600–170 nm. High resolution transmission electron microscopy image shows that each sphere is made up of numerous nanoparticles of average diameter 4 nm. The XRD patterns, Scanning electron microscopy and transmission electron microscopy micrographs of doping of Ni in ZnO are confirmed the formation of micro-spheres. Furthermore, the UV–vis. spectra and photoluminescence spectra of the Ni-doped ZnO nanoparticles were also investigated. The band gap of the nanoparticles can be tuned in the range of 3.55–3.36 eV by the use of the dopants. 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.     

Magnetodielectric properties of rare earth metal-doped BiFeO3 nanoparticles

Pure and rare earth metal ions (Gd³⁺, Tb³⁺, Dy³⁺)-doped BiFeO₃ nanoparticles have been synthesized by the sol–gel method. The effect of doping of rare earth metal ions on structural, magnetic, dielectric and magnetodielectric properties of synthesized nanoparticles have been investigated. Synthesized nanoparticles have been found to be possessing spherical morphology, with average particle size, 25–46 nm. Structural study confirms that 15 % mole fraction doping of the rare earth metal ions results in structural transformation from rhombohedral to orthorhombic phase. Magnetic study reveals that the synthesized nanoparticles exhibit well saturated ferromagnetic magnetic loops. Dielectric measurements show that doping of rare earth metal ions results in high dielectric constant as compared to that of pure BiFeO₃. Magnetoelectric coupling in the synthesized nanoparticles, established by performing magnetodielectric measurements, reveals that the doped nanoparticles exhibit high magnetodielectric coefficient as compared to its pure form. The high value of saturation magnetization, 5.22 emu/g, dielectric constant, 900 and magnetodielectric coefficient, 5.82 %, have been observed in Dy-doped BiFeO₃ nanoparticles. The observed trend in the properties of the synthesized nanoparticles has been explained on the basis of doping as well as size of the synthesized nanoparticles.     

Physical and magnetic properties of (Co, Ag) doped ZnO nanoparticles

Undoped and (Co, Ag) co-doped ZnO nanostructure powders are synthesized by chemical precipitation method without using any capping agent and annealed in air ambient at 500 °C for 1 h. Here, the Ag concentration is fixed at 5 mol% and Co concentration is increased from 0 to 5 mol%. The X-ray diffraction studies reveal that undoped and doped ZnO powders consist of pure hexagonal structure and nano-sized crystallites. The novel Raman peak at 530 cm^?1 has corroborated with the Co doped ZnO nanoparticles. Moreover, the PL studies reveal that as the Co doping concentration increases and it enters into ZnO lattice as substitutional dopant, it leads to the increase of oxygen vacancies (Vo) and zinc interstitials (Zn_i). From the magnetization measurements, it is noticed that the co-doped ZnO nanostructures exhibit considerably robust ferromagnetism i.e. 4.29 emu g^?1 even at room temperature. These (Co, Ag) co-doped ZnO nanopowders can be used in the fabrication of spintronic and optoelectronic device applications.     

Low temperature produced calcium-doped zinc oxide thick film via screen printing technique as thermal interface material in LED application

Pure and calcium-doped zinc oxide thick films were deposited on Aluminium substrate by screen printing technique using nanocrystalline powder synthesized from co-precipitation method. Shear thinning phenomenon with increment of shear rate was observed during the rheological analysis for all pastes. X-ray diffraction results confirmed the formation of ZnO with preferred orientation along (101) plane. Peak shifting to lower angle was observed upon increment of doping concentration of calcium. Crystallite size of doped ZnO powder decreased in the range (from 35.4 to 42.4 nm) from 116.1 nm of pure ZnO. Surface morphology analysed by FESEM had revealed the reduction of voids with increasing doping concentration up to 7 wt% of doping, followed by a slightly increase in the number of voids at 9 wt% doping. AFM analysis showed that the surface roughness of films exhibited a decreasing trend with the increase of calcium dopant until 7 wt% but became rougher at 9 wt%. Peaks shifting of ZnO to lower wavenumber revealed by FTIR study indicated that doping had affected the lattice structure of ZnO in the films. Thermal characterization showed the introduction of calcium dopant had increased the thermal resistance of the thick films. This led to a better junction temperature (T_j) of LED of 46.4?°C when compared with T_j of pure ZnO film at 47.3?°C.     

Thermal annealing induced structural and optical properties of Ca doped ZnO nanoparticles

In this letter, the effects of annealing on structural and optical properties of Ca doped ZnO nanoparticles have been investigated. X-ray diffraction analysis reveals that the prepared particles are in hexagonal wurtzite structure and formation of secondary phase related to the Calcite was found after thermal annealing. UV–Vis measurements show free exciton absorption band appeared at 372 nm and increase of band gap with annealing of samples. Room temperature photoluminescence (PL) spectrum of the prepared Ca doped ZnO nanoparticles shows bands which belong to the near band edge emission at 377 nm and green emission at 556 nm. Annealed samples exhibit enhancement in the blue emission band. Raman spectra show the increment in the electron–phonon coupling value with annealing.     

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.     

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.     

Strong room temperature ferromagnetism in chemically precipitated ZnO:Co2+:Bi3+ nanocrystals for DMS applications

Well crystalline Co-Bi co-doped ZnO nanostructures with various concentration of Bi were synthesized by simple chemical precipitation technique using metal nitrate precursors. The structural and magnetic properties of the samples calcined at 300 °C for 6 h has been studied comprehensively. X-ray diffraction patterns of the pure and Co-with Bi doped samples have shown the well crystalline diffraction peaks corresponds to the characteristic wurtzite ZnO crystal structure. Aggregated nano particles have emerged with flower like morphology and it can be seen from the scanning electron microscopy and transmission electron microscopy. The average particle diameter was estimated and found to be 25–35 nm. Tunable optical band gap related to an additional electron state created by dopant was observed from the UV–Visible spectra. Typical PL emission in the UV, visible and continuous deep level emission further demonstrates that the potential application of the material in optoelectronics. Excellent ferromagnetic features of the material at room temperature reveal the additional carrier induced exchange interaction could enhance the ferromagnetism in co-doped ZnO nanostructure. The addition of Bi at 3⁺ states can act as donor within the semiconductor which provides the additional electron charge carrier that could involve directly to the exchange interaction effectively at certain limit and enhances the ferromagnetism. At higher doping concentration the formation of diamagnetic Bi₂O₃ secondary phase have contributed to change the ferromagnetic behaviour of the sample. From this study it is suggested that this kind of combined ferromagnetism and excellent optical tunability of the Bi co-doped ZnO:Co system will be the potential material for future magneto-opto-electronic devices.     

Structural, optical, and magnetic characterization of Co and N co-doped ZnO nanopowders

Co and N co-doped ZnO nanopowders with Co and N concentration 4, 6, and 8 mol% were synthesized by sol–gel method. Powder X-ray diffraction reveals that Co and N co-doped ZnO crystallize in wurtzite structure having space group C _6v . Photo-luminescence studies show the reduction in band gap with increase in concentration of dopants. Micro Raman studies show the red shift for 1LO phonon peak with increase in doping, generally credited to the stress caused by lattice mismatch due to N doping in ZnO. X-ray absorption spectroscopy reveals that Co replaces the Zn atoms and N replace the O atoms in the host ZnO lattice. Magnetic studies show that Co and N co-doped ZnO nanopowders exhibit ferromagnetic character at room temperature.     

Red luminescence from hydrothermally synthesized Eu-doped ZnO nanoparticles under visible excitation

Eu-doped ZnO nanoparticles were synthesized by hydrothermal method. The Eu-dopant concentration has been varied by varying the amount of Eu-dopant concentration. These nanoparticles were structurally characterized by X-ray diffraction, transmission electron microscopy and selected area electron diffraction and it confirms the formation of nanoparticles having standard wurtzite structure. Photoluminescence studies show that these nanoparticles exhibit a sharp red luminescence due to the intra-4f transitions of Eu³⁺ ions at an excitation of 397 nm and 466 nm. Luminescence quenching is observed in the nanoparticles as the Eu-dopant concentration increases. Incorporation of Eu in the nanoparticles was confirmed by the energy dispersive X-ray studies.     

A Novel one-step synthesis of Ag-doped ZnO nanoparticles for high performance photo-catalytic applications

In this report, pure and silver (Ag) doped zinc oxide (ZnO) nanoparticles with various concentrations of silver (5 and 10 wt%) was successfully synthesized by a novel and one step microwave irradiation method. Powder X-ray diffraction results indicates that all of the as-synthesized samples including the highest Ag (10 wt%) doping have a hexagonal wurtzite type structure and average crystalline size was found to be 28, 21 and 16 nm for pure and Ag doped ZnO respectively. Spherical shaped morphology with an average diameter of around 32–13 nm was observed by Transmission electron microscope analysis. UV–Vis spectra revealed that, Ag doped samples exhibits a red shift in the absorption band edge with increasing Ag dopant concentration. The photocatalytic degradation of methyl violet (MV), phenol and rhodamine B (RHB) was investigated by using Ag-ZnO catalyst under UV light irradiation. The result showed that the photocatalytic property was significantly improved by Ag doping. The improved photocatalytic mechanism by Ag doping was also discussed. The samples were further characterized by photoluminescence spectra and Fourier Transform Infrared Spectra (FTIR) analysis.     

Enhancement of room temperature ferromagnetism in Cd1−xNixSe nanoparticles

Cd_1?xNi_xSe (x = 0.0, 0.02, 0.05 and 0.1) nanoparticles have been synthesized by chemical route. X-ray diffraction analysis shows crystalline nature of synthesized nanoparticles possessing wurtzite phase having hexagonal structure. Transmission electron microscopy depicts spherical morphology and uniform particle size distribution of pure and Ni-doped CdSe nanoparticles. The blue-shift in band gap has been observed with Ni-doping concentration. Photoluminescence study shows the presence of intrinsic defects (V_Cd–V_Se) in the synthesized nanoparticles. Electron spin resonance (ESR) analysis reveals the long range ferromagnetic ordering in pure and doped nanoparticles. ESR study also indicates that Ni ions exist in +2 oxidation state in host nanoparticles. The magnetic hysteresis (M-H) loops display ferromagnetism at room temperature in pure and Ni-doped CdSe nanoparticles. The increase of ferromagnetic behavior has been observed with Ni-doping concentration. M-H analyses indicate that defects and carrier mediated exchange interactions are responsible for ferromagnetic ordering, in the present study.     

Fe dopants enhancing ethanol sensitivity of ZnO thin film deposited by RF magnetron sputtering

Pure and 5 % Fe-doped ZnO thin films (TFs) have been successfully deposited on Al₂O₃ substrate from pre-doped target material by RF magnetron sputtering technique. X-ray diffraction (XRD) patterns confirm the formation of both films in single phase wurtzite structure without any extra impurity peak. The calculated average crystallite sizes are found to be 22 and 17 nm for pure and Fe-doped ZnO TFs, respectively. The broadening in XRD peaks of Fe-doped ZnO TF occurs due to decrease in crystallite size and increase in lattice strain. Field emission scanning electron microscopy images exhibit that the particles growth in Fe-doped ZnO TF is more uniform and smaller than pure ZnO. Energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy results confirm the existence of Fe dopants into ZnO matrix. The doping effect enhances the sensitivity of ZnO sensor almost three times for ethanol gas sensing, the improvement in the response time and recovery time is noticeable as the size reduction effect increases the surface to volume ratio, and resulting more numbers of ethanol gas molecules are adsorbed to produce a higher concentration of oxygen ions which leads a larger deviation in capacitance.     

A selective ethanol gas sensor based on spray-derived Ag–ZnO thin films

A simple and cost-effective spray pyrolysis technique was employed to synthesize silver-doped zinc oxide (Ag–ZnO) thin films on the glass substrates from aqueous solutions of zinc acetate and silver nitrate precursors at 450 °C. The effects of Ag doping on structural, morphological, and gas-sensing properties of films were examined. The X-ray diffraction spectra of the Ag–ZnO films showed the polycrystalline nature having hexagonal crystal structure. Scanning electron microscopy (SEM) images of the pure ZnO films revealed the uniform distribution of the spherical grains (~80 nm size). Tiny Ag nanoparticles are clearly visualized in the SEM of Ag–ZnO films. The investigation of the effect of Ag doping on the gas-sensing properties of the Ag–ZnO revealed that the 15 % Ag-doped ZnO sample has the highest gas sensitivity (85 %) and excessive Ag doping in ZnO degraded the gas sensitivity. A possible mechanism of Ag–ZnO-based sensor sensitivity to the target gas is also proposed.     

Study on CaCO3-coated ZnO nanoparticles based dye sensitized solar cell

Dye sensitized solar cells (DSSCs) have been fabricated using ZnO and CaCO₃-coated ZnO nanoparticles. The effect of CaCO₃ coating on the performance of DSSC has been investigated. CaCO₃-coated ZnO nanoparticles have been synthesized by hydrothermal method. X-ray diffraction patterns of synthesized nanoparticles reveal that the ZnO and CaCO₃-coated ZnO nanoparticles have respectively wurtzite and rhomb-centred structure and both having hexagonal phase. Transmission electron microscopy study reveal that ZnO and CaCO₃-coated ZnO nanoparticles possess spherical symmetry and have average particle size respectively 6.2 and 6.7 nm. In case of CaCO₃/ZnO nanoparticles, the quenching in photoluminescence emission intensity has been attributed to the decrease in recombination rate of photo-generated electron–hole pairs. UV–Vis absorption spectra, confirms that the electrodes fabricated from the CaCO₃-coated ZnO nanoparticles have higher absorbance that shows their higher dye adsorbing power. The use of CaCO₃ coating has been found to enhance the efficiency of DSSC by over 100 %.     

Photoluminescence and gas sensing study of nanostructured pure and Sn doped ZnO

The nanostructured pure and Sn doped ZnO have been synthesized by the thermal evaporation technique. The influence of Sn on the morphology and structure is investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis techniques. The SEM images indicate change in the growth pattern from nanowires of pure ZnO to tetrapods for Sn doped ZnO. Pure ZnO nanowires exhibit selective response towards acetone vapors while on Sn doping the response decreases. The non-stiochiometry and the morphology of ZnO are probably responsible for such a difference in gas response. However increase in temperature doesn't improve the sensing behavior. The photoluminiscence (PL) studies reveal UV emission in pure ZnO which shifts to green emission on doping of Sn.