Search

ZnO nanoparticles at different temperatures were synthesized by using the combustion method. The effect of synthesis temperature on the properties of the nanoparticles was studied by using XRD, FESEM, EDS, TEM, photoluminescence (PL), Raman, diffuse reflectance spectra (DRS), and VSM characterization techniques. The XRD results reveal that the grown nanoparticles have a hexagonal wurtzite structure without any impurities and agreed with EDS results. FESEM and TEM micrographs show that the ZnO nanoparticles possess a spherical shape with agglomeration free, and the size increases with increase of synthesis temperature. From DRS studies, it was noticed that the band gap decreases with increase of synthesis temperature. In PL studies, blue peak at 465 nm may be due to defect-related transitions. A sharp intense peak in Raman spectra at 485 cm−1 represents E2H mode is a characteristic of a hexagonal wurtzite structure. The magnetic studies show that the magnetization decreases from 0.0172 to 0.0042 emu/g as the synthesis temperature increases from 400 to 550 °C. ZnO synthesized at 500 °C has a large squareness ratio. These materials are potential candidates for memory devices.

Nanoparticles (Nps) of Ba (0, 1 to 5 at.%)-doped BiFeO3 were synthesized by a sol-gel route at 100 °C using tartaric acid as a chelating agent. The obtained results were studied by using XRD, SEM with EDAX, TEM, UV-vis diffusion reflectance spectra, VSM, and impedance analyzer. EDAX spectra confirmed the presence of Bi, Ba, and Fe in the samples. X-ray diffraction studies showed that BiFeO3 and Bi1−xBaxFeO3 samples exhibited the expected rhombohedral perovskite structure up to a Ba concentration of 3%, whereas 4 and 5% of Ba concentration exhibited the tetragonal phase. TEM studies indicate the particle sizes in the range of 08–28 nm. Reflectance spectra measurements showed a decrease in band gap with increasing Ba concentration. Magnetic properties indicated that the undoped BiFeO3 and Ba-doped BiFeO3 samples were ferromagnetic at room temperature. The dielectric constant (e′) and loss (e″) show large dispersion behavior. The dielectric constant increases with an increase of dopant concentration, but a very high value of the dielectric constant was noticed for x = 0.05.

Here in, we synthesized pure BiFeO3 (BFO) and Bi0.8-XCaXEr0.2FeO3 (x = 0.0, 0.05, 0.1, and 0.15 at.%) nanoparticles using sol–gel technique and investigated their optical, magnetic, and electrical properties. X-ray diffraction studies reveals structural transformation in BFO from the rhombohedral structure to orthorhombic, without forming any defect phases, with the doping of Er or Ca/Er into BFO. EDX analysis confirms the presence of doped elements (Er and Ca) along with the Bi, Fe and O elements corresponding to BFO host material. TEM images indicate the significant reduction in particle size with increasing the Ca dopant concentration. Further, the band gap of pure BFO nanoparticles (2.30 eV) decreases notably to a minimum of 1.81 eV for Ca and Er co-doped BFO nanoparticles. All samples exhibited the ferromagnetic behavior, Bi0.8-XCaXEr0.2FeO3 (x = 0.05 at.%) nanoparticles yielded 2.9 times higher saturation magnetization compared to BFO nanoparticles. In addition, the conductivity increases by 11.8 times for Bi0.8-XCaXEr0.2FeO3 (x = 0.05 at.%) nanoparticles compared to BFO nanoparticles.

In the era of modern technology, the development of spintronic devices using diluted magnetic semiconductor nanoparticles has drawn significant attention from the world researchers. In this work, we report on novel Cu1−x Mn x S (x = 0.00, 0.01, 0.03 and 0.05) compounds synthesized at room temperature through a simple precipitation method via EDTA as a capping agent. XRD patterns suggested that the entire synthesized nanoparticles exhibit covellite-phase hexagonal configuration like CuS. Reflectance measurements indicated energy band gap reduction by augmentation of Mn content. Photoluminescence spectra of prepared nanoparticles showed strong blue, green and weak yellow emissions at 471, 533 and 583 nm, respectively. The room-temperature VSM measurements suggested that bare CuS showed a diamagnetic nature, while Mn-doped CuS nanoparticles exhibited paramagnetism, which is enhanced with increasing Mn dopant concentration.

Multiferroic BiFeO3 and Bi0.8-XGdXEr0.2FeO3 (X = 0.0, 0.05, 0.1 & 0.15) nanoparticles have been prepared by sol-gel technique. The effect of Gd content (in Gd/Er co-dopant) on the structural, magnetic, dielectric, and optical properties of the BiFeO3 materials has been studied. X-ray diffraction analysis revealed rhombohedral to orthorhombic phase transition of BiFeO3 when doped with Er or Er/Gd. All samples composed of aggregated spherical nanoparticles and the size of the particles is decreased with increasing the Gd content in Gd/Er co-doped BiFeO3 nanoparticles. Energy dispersive spectra confirm the presence of all the selective elements in synthesized samples and are in near stoichiometric ratio. The Fourier transform Infrared spectra confirmed the presence of functional groups of elements of synthesized nanoparticles only. Optical properties of the samples, as studied by UV–visible spectroscopy, showed the decreased optical band gap with increasing the Gd content in Bi0.8-XGdXEr0.2FeO3 nanoparticles. The Er/Gd co-doping in BiFeO3 had a significant effect on the magnetic properties and effectively reduced the leakage current. The simultaneous enrichment of magnetic and electric properties indicates the potential application of Bi0.8-XGdXEr0.2FeO3 (X = 0.0, 0.05, 0.1 & 0.15) nanoparticles in future multifunctional devices.

Single crystalline nano-sized multiferroic BiFeO3 (BFO) powders were synthesized through simple chemical co-precipitation method using polyethylene glycol (PEG) as capping agent. We obtained pure phase BiFeO3 powder by controlling pHand calcination temperature. From X-ray diffraction studies the nanoparticles were unambiguously identified to have a rhombohedrally distorted perovskite structure belonging to the space group of R3c. No secondary phases were detected. It indicates single phase structure. EDX spectra indicated the appearance of three elements Bi, Fe, O in 1:1:3. From the UV-Vis diffuse reflectance spectrum, the absorption cut-off wavelength of the BFO sample is around 558nm corresponding to the energy band gap of 2.2 eV. The size (60-70 nm) and morphology of the nanoparticles have been analyzed using transmission electron microscopy (TEM).   Linear M−H behaviour and slight hysteresis at lower magnetic field is observed for BiFeO3 nanoparticles from Vibrating sample magnetometer studies. It indicates weak ferromagnetic behaviour at room temperature. From dielectric studies, the conductivity value is calculated from the relation s = L/RbA Sm-1 and it is around 7.2 x 10-9 S/m.

We are the first to report a systematic study on the structural, optical and magnetic properties of cobalt and aluminum codoped CdS nanoparticles synthesized by simple co precipitation method. XRD patterns confirm the formation of single phase cubic structure for all the compositions. From diffuse reflectance spectra (DRS), three characteristic reflectance minima peaks present for all samples at 686, 729 and 750 nm associated with d–d transitions 4 A 2 (F)→3/2U 1 , 4 A 2 (F)→E 11 and 4 A 2 (F)→5/2U 1 confirm the substitution of Cd 2+ ion by Co 2+ ion in CdS. Blueshift of absorption edge with the incorporation of Al into CdS:Co nanoparticles is the evidence for the substitution of Cd 2+ ion by Al 3+ ion. Bandgap widening observed with increasing Al content can be explained by Burstein–Moss effect. Photoluminescence spectra revealed the transition of defect related green emission into near band edge blue emission by aluminium codoping, which can be attributed to the reduction of defect levels. In the present study, Cd 0.96− x Co 0.04 Al x S nanoparticles system is found to be capable of retaining a part of room temperature ferromagnetic (RTFM) portion even at x =0.07.

Diluted magnetic semiconducting (DMS) ZnS:Ni (Ni=0, 1, 3 and 5 at%) nanoparticles were synthesized by the refluxing technique at 80 °C. X-ray diffraction studies showed that undoped ZnS and Ni doped ZnS nanoparticles exhibited the expected zinc blende structure. X-ray photoelectron spectroscopy results revealed that the Ni ions existed in a +2 state in these nanoparticles. Reflectance measurements showed a decrease in band gap with increasing Ni concentration. Room temperature photoluminescence (PL) studies indicated that all the samples exhibited broad and asymmetric PL peaks covering a wide visible range. Gaussian fitting of PL data resulted in three deconvoluted peaks corresponding to blue and green emissions. Dramatic enhancement in fluorescence efficiency was observed in the doped ZnS nanoparticles indicating their possible applications in photoluminescent devices. Magnetic studies revealed that all the doped samples exhibited carrier mediated ferromagnetism at room temperature. Saturation magnetization ( M s ) increased with increasing Ni content reaching a maximum for 3 at% Ni and decreased for samples of 5 at% Ni.

Un-doped and Al doped ZnS nanoparticles were prepared via an efficient and low cost chemical co-precipitation method using Poly Ethylene Glycol (PEG) as stabilizer. In the present study effect of Al concentration on the morphological, structural, and optical properties is studied using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Raman analysis, Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) studies. XRD, TEM, FTIR and Raman analysis indicated the formation of impurity-free nanocrystals with cubic structure. DRS studies revealed that as the Al dopant concentration increases the band gap increases in the range of 3.73–4.01 eV. The PL spectra of all samples exhibit a broad emission band in the range of 350–650 nm. The Gaussian fitting emission bands for ZnS are located at 382, 398, 417 and 445 nm. For Al doped ZnS nanoparticles in addition to the pure ZnS peaks two extra peaks are observed at 472 and 493 nm. Further, enhanced photoluminescence was observed with increasing Al content up to 8 at.% and beyond this photoluminescence quenching was noticed.

Zn0.97−xAlxCr0.03S (x=0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.12) nanoparticles were synthesized by the chemical co-precipitation method using Ethylene Di-amine Tetra Acetic acid (EDTA) as capping agent. The effect of Al co-dopant on the structural, optical and magnetic properties is discussed on the basis of EDS, SEM, XRD, TEM, SAED, DRS, FTIR, PL, EPR and VSM results. EDS studies indicated the presence of Zn, S, Cr and Al elements in the samples with near stoichiometry. XRD, TEM and SAED studies revealed that samples of all concentrations exhibited cubic structure. The absorption edge in DRS spectra shifted towards higher wavelength with increasing Al concentration indicating a decrease of band gap from 4.05 to 3.85 eV. Enhanced photoluminescence was observed with increasing Al concentration up to 4 at% and beyond this photoluminescence quenching was observed. FTIR spectral studies indicated that EDTA simply co-exists on the surface of the nanoparticles and acts as the capping agent preventing agglomeration of the nanoparticles. EPR spectral studies indicated that the EPR signal intensity, linewidth and number of spins increased with Al concentration. VSM studies revealed that Al co-doping suppressed the room temperature ferromagnetism in ZnS:Cr nanoparticles.

Photocatalytic H2 generation through water splitting using heterogeneous semiconductor nanostructures under the beneath of sunlight is a significant route for alternation of renewable energy. In this perception we fabricated novel hierarchical CdS/MoS2-CoSe2 nanostructures via facile solvothermal route combined with ultra-sonication technique. Optical studies explored that synthesized nanostructures are most reliable host lattices for harvesting of visible light owing to their optimum energy band gap. The MoS2-CoSe2 encumbered on CdS nanorods component provided immense of hydrogen evolution (191.5 mmolg−1 h−1) with outstanding stability. It is noteworthy that the observed H2 evolution rate is much higher in synthesized structures as compared to numerous reported CdS based nanohybrids. The robust H2 evolution rate and outstanding stability may be owing to fast charge carriers separation and migration between CdS and MoS2-CoSe2, creation of huge surface area and broad light harvesting nature. It is evident from PL, optical, photocurrent and impedance results. From the obtained results we believe that the proposed design strategy is preferable path way to develop new type of photocatalysts with robust H2 evolution rate.

Pure and cobalt doped CdS nanoparticles were successfully synthesized by surfactant assisted simple chemical co-precipitation method. Size of the particles around 3 nm and cubic zincblende structure were revealed by the X-ray diffraction pattern. From TEM images particle size was found be around 4–5 nm. Redshift of absorption edge and bandgap narrowing (from DRS spectra) can be attributed to increase in the carrier concentration by the inclusion of cobalt ions and creation of defect levels in the bandgap. Three characteristic reflectance minima only in cobalt doped samples can be related to d–d transitions 4 A 2 (F) → 3/2U 1 , 4 A 2 (F) → E 11 and 4 A 2 (F) → 5/2U 1 . Strong green emission was exhibited by all the samples through photoluminescence studies can be attributed to the transitions of trapped electrons from donor levels to the valance band or mid gap surface states. Intensity of the luminescence peak was found to be maximum for 2% and quenching was observed beyond 2%. Well defined room temperature ferromagnetic hysteresis loop was observed for 4% Co doped CdS nanoparticles. Saturation of magnetization M S and retentivity M R mounts up with cobalt content up to 4% and then decreases.

Cadmium sulfide (CdS) semiconductor nanocrystals (NCs) doped with Fe3+ have been synthesized via a solution-based method utilizing dopant concentrations of (0–5%) and employing 2-mercaptoehonal as a capping agent. X-ray diffraction (XRD) results showed that the undoped CdS NCs are in mixed phase of cubic and hexagonal, where as the doped CdS NCs are in hexagonal phase. The crystallite size was increased from ∼1.2 nm to ∼2 nm. Diffuse reflectance spectroscopy studies (DRS) reveals that the band gap energy was decreased with Fe doping and it lies in the range of 2.58 - 2.88 eV. Photoluminescence (PL) spectra of undoped CdS NCs show a strong green emission peak centered at 530 nm and a weak red emission shoulder positioned at 580 nm. After doping all the luminescence intensity was highly quenched and the green emission peak was shifted to orange region (580 nm), but the position of weak red emission shoulder was unaltered with doping. FTIR studies revealed that the NCs were sterically stabilized by 2-mercaptoethanol. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Zn1−xCrx S nanoparticles with x = 0.00, 0.005, 0.01, 0.02 and 0.03 were synthesized by chemical co-precipitation method at room temperature for the first time. Ethylene diamine tetraacetic acid was used as stabilizer. Energy dispersive analysis of X-rays confirmed the presence of Cr in the samples. The samples were characterized by scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy and optical absorption studies. XRD and selected area electron diffraction results showed that the samples of all compositions crystallized in cubic structure and the lattice parameters decreased linearly with increase in Cr content following Vegard's law indicating that the Cr ions have substituted for Zn in the ZnS lattice. The particle size estimated from XRD was in the range 6–10 nm.The optical absorption studies on the doped samples indicated that the absorption edge blue shifted with respect to those of bulk and nanocrystalline ZnS. The bandgap increased with increasing Cr concentration in a narrow range 3.81–4.03 eV. Photolumonesence studies showed blue emission with appreciable luminescence quenching with increasing Cr concentration. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanoparticles of Zn1−xCrxS (x=0.00, 0.005, 0.01, 0.02 and 0.03) were prepared by a chemical co-precipitation reaction from homogenous solutions of zinc and chromium salts. These nanoparticles were sterically stabilized using 2-mercaptoethanol. Here a study of the effect of Cr doping on structural, morphological and optical properties of nanoparticles was undertaken. Elemental analysis, morphological, structural and optical properties have been investigated by energy dispersive analysis of X-rays (EDAX), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy .EDAX measurements confirmed the presence of Cr in the ZnS lattice. XRD showed that ZnS:Cr nanoparticles crystallized in zincblende structure with preferential orientation along (1 1 1) plane. The average sizes of the nanoparticles lay in the range of 3–6 nm and lattice parameters were in the range of 5.2–5.4 A. Lattice contraction was observed with an increase of Cr concentration. The particle size and lattice parameters obtained from TEM and SAED images were in agreement with the XRD results. The absorption edge shifted to lower wavelengths with an increase in Cr concentration as per UV–Vis spectroscopy. The band gap energy values were in the range of 3.85–4.05 eV. This blueshift is attributed to the quantum confinement effect.

(ZnSe) x (CdS) 1 − x films (about 6 μm thick) in the entire range of x have been formed on glass substrates kept at 470 K by thermal evaporation. All the films exhibited n-type conductivity. X-ray diffraction (XRD) studies showed that films with 0 ⩽ x ⩽ 0.70 were polycrystalline with the wurtzite phase, whereas films with 0.8 ⩽ x ⩽ 1.0 crystallized in the zincblende phase. The lattice parameter varied linearly with x following Vegard's law in both the structures. The direct optical band gaps varied non-linearly, showing a downward bowing with increasing x . The bowing parameter was found to be about 0.39 eV. The structural transformation region of x obtained by analysing band gap data was found to agree well with that obtained from XRD studies.

(ZnSe) x (CdS) 1 − x films (about 6 μm thick) in the entire range of x have been formed on glass substrates kept at 470 K by thermal evaporation. All the films exhibited n-type conductivity. X-ray diffraction (XRD) studies showed that films with 0 ⩽ x ⩽ 0.70 were polycrystalline with the wurtzite phase, whereas films with 0.8 ⩽ x ⩽ 1.0 crystallized in the zincblende phase. The lattice parameter varied linearly with x following Vegard's law in both the structures. The direct optical band gaps varied non-linearly, showing a downward bowing with increasing x . The bowing parameter was found to be about 0.39 eV. The structural transformation region of x obtained by analysing band gap data was found to agree well with that obtained from XRD studies.

Thin films (~200 nm thick) of (ZnTe) x (CdSe) 1− x in the entire range of composition (0 ⩽ x ⩽ 1) were prepared by thermal vacuum evaporation maintaining the glass substrates at 303 and 553 K. XRD studies showed that the films were polycrystalline. Wurtzite structure was found in compositions up to x = 0.5. Beyond this composition the zincblende structure was observed. A structural discontinuity was found in a very narrow range of x . Energy gaps estimated from photoconductivity spectral response and optical transmittance spectra were nearly the same and varied non-linearly with composition. The bowing parameters for films prepared at 303 and 553 K were found to be 1.03 and 1.31 eV, respectively. The structural discontinuity and bowing parameter are discussed in detail. Crystallinity (grain size), lattice parameters and bandgap were found to increase with T s .

The titlematerial is one of the least studied among the II-VI alloy systems. So far it has not been possible to prepare ZnTe in n-type and CdSe in p-type with appreciable conductivities. Moreover ZnTe crystallises in zincblende whereas CdSe crystallises in wurtzite structure. Because of the varied nature of the end compounds, an attempt has been made to prepare single crystals of (ZnTe)x(CdSe)1−x in the entire range of ‘x’. The alloy material in the entire range Xof composition in the single crystalline form was grown by a modified Piper-Plich method. The grown crystals of this alloy system have been subjected to chemical analysis. DTA and DTG studies carried out on these alloys did not show any phasec transitions. However two exothermic peaks associated with increase in mass were noticed. This has been attributed to oxidation effects of Se/Te or Cd/Zn. XRD data though showed some regularity near end compositions there is still some ambiguity for the middle compositions. Energy gap obtained from reflection spectra and also photocurrent spectral response showed bowing. However, there is a marked different feature at one of the end regions. The growth and the results of all the above mentioned investigations are presented and discussed in this paper.