Investigations on structural and optical properties of Zn1−xGdxS nanoparticles

Zn_1−xGd_xS (x = 0.00, 0.02 and 0.04) nanoparticles were synthesized by facile chemical co-precipitation method using PVP as a surfactant. ZnS nanoparticles could be doped with Gd ions during synthesis without altering the XRD patterns of ZnS. Also, the pattern of the powders showed cubic zincblende structure. The particle size obtained from the XRD studies lies in the range 3-5 nm, whereas from TEM analysis it is 4 nm for x = 0.02 sample. The UV-Vis absorption spectra revealed that Zn_1−xGd_xS nanoparticles exhibit strong confinement effect as the blue shift in the absorption spectra with that of the undoped ZnS. The photoluminescence spectra showed enhanced luminescence intensity and the entry of Gd into host lattice.     

Luminescence characteristics of Ca1−xSrxS:Ce nanophosphors

Luminescence characteristics of Ca_1−xSr_xS:Ce (x = 0, 0.25, 0.50, 1) nanophosphors have been investigated. XRD of all the samples show a single cubic phase of Ca_1−xSr_xS:Ce. TEM micrographs exhibit the rod like structure of the samples with a decrease in diameter with decreasing amount of Ca. The results of TEM were found to be in good agreement with the XRD results. The photoluminescence spectrum comprises of a main peak in the range 480-510 nm with a shoulder in the range 530-565 nm, which may be ascribed to transitions from 5d-4f levels of cerium in the mixed host lattice. The red shift in the emission wavelength with increasing Ca content may be correlated with the change in crystal field of mixed host lattice for different Ca and Sr concentrations. We have also investigated TL response of Ca_1−xSr_x:Ce to ⁶⁰Co-γ rays. All the samples with different Sr and Ca contents show different TL response. TL response for the sample with x = 0.75 shows the simplest TL glow curve with the maximum TL intensity, for which we have calculated the activation energy using glow curve deconvolution functions.     

Adsorption and photocatalytic degradation of methylene blue on Zn1−xCuxS nanoparticles prepared by a simple green method

Nanoparticles of Zn_1−xCu_xS with various dopant contents (0 ≤ x ≤ 0.15) were prepared in water by refluxing for 90 min at about 95 °C. Powder X-ray diffraction (XRD) patterns of the nanoparticles demonstrate that loading of Cu²⁺ ions does not change the crystal structure of ZnS. Scanning electron microscopy (SEM) images demonstrate that size of the nanoparticles decreases with increasing Cu²⁺ ions. UV-Vis diffuse reflectance spectra (DRS) of the nanoparticles show significant absorption in visible light region. Adsorption capacity of the nanoparticles for methylene blue (MB) increases with mole fraction of copper ions. Photocatalytic activity of the nanoparticles toward photodegradation of MB was evaluated under visible light irradiation. The results indicate that Zn_0.85Cu_0.15S nanoparticles exhibit highest photocatalytic activity among the prepared samples. Moreover, effects of refluxing time applied for preparation of the nanoparticles and calcination temperature were investigated.     

Photoluminescence and magnetic properties of Fe-doped ZnS nano-particles synthesized by chemical co-precipitation

This paper is focusing on the synthesis of Zn_1−xFe_xS nano-particles with x = 0, 0.1 and 0.2 by chemical co-precipitation method, the prepared of which are characterized by XRD, EDS, TEM, PL, magnetization versus field behavior and M-T curve. In the XRD patterns, Zn_1−xFe_xS nano-particles are shown of cubic zinc blende structure, and the broadening diffraction peaks consistent with the small-size characteristic of nano-materials. The diameter of nano-particles is between 3.3 and 5.5 nm according to the HR-TEM images. The EDS data confirm the existence of Fe ions in Fe-doped ZnS nanoparticles. There we found that Fe-doping did not import new energy bands or defect states, but reduced the intensity of PL peaks. The magnetization versus field behaviors were illustrated by the M-H curves at both 5 K and 300 K, respectively, where no remanence or coercive force was observed. This phenomenon indicates that the Zn_1−xFe_xS (x = 0.1) nano-particles are superparamagnetic. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves further reveal that the blocking temperature (T_B) of the superparamagnetic behavior might be below 5 K.     

Growth, structural and optical properties of non-stoichiometric CuIn(S1−xSex)2 thin films deposited by solution growth technique for photovoltaic application

Polycrystalline thin films of p-CuIn(S_1−xSe_x)₂ have been deposited by a solution growth technique. The deposition parameters such as pH, temperature and time have been optimized. In order to achieve uniformity of thin film, triethanolamine (TEA) has been used. As deposited films have been annealed at 450 °C in air for 5 min. The surface morphology, compositional ratio, structural properties have been studied by SEM, EDAX and XRD technique, respectively. It has been found that films have chalcopyrite structure with the lattice parameters a=5.28 Å and c=11.45 Å at composition x=0.5. The grain size of all composition x measured from SEM and XRD is varied in between 450 and 520 nm. The optical transmittance spectra have been recorded in the range 350-1000 nm. The absorption coefficient has been calculated at the absorption edge for each of the composition x and it is in the range of 10⁴ cm⁻¹. The material shows the direct allowed band gap, which varies from 1.07 to 1.44 eV with change in composition (0≤x≤1.0). These parameters are useful for the photovoltaic application.     

Growth and characterization of CuxS (x=1.0, 1.76, and 2.0) thin films grown by solution growth technique (SGT)

Thin films of Cu_xS (x=1.0, 1.76, and 2.0) were grown by solution growth technique (SGT). The deposition parameters such as pH of solution, deposition time, and deposition temperature were optimized. The deposited films were annealed in Ar atmosphere at 250 °C. The changes in structural and optical transport phenomenon of annealed films have been studied. The surface morphology and composition of films were studied by SEM micrographs and EDAX analysis, respectively, and the surface roughness was calculated by atomic force microscopy (AFM). The XRD study showed the polycrystalline nature of annealed film. The lattice parameters of different phases of the material were calculated from the XRD pattern. The absorption coefficient varies in the range of 1×10⁵-6×10⁵ cm⁻¹. The optical bandgaps of CuS, Cu_1.76S, and Cu₂S are 1.72, 2.11, and 2.48 eV, respectively.     

The effects of Cr-doping on the room temperature ferromagnetism of chemically synthesized CeO2−δ nanoparticles

We report an investigation of the nature of room-temperature ferromagnetism enhancement in Ce_1−xCr_xO_2−δ nanoparticles (0.00≤x≤0.05), synthesized by a sol–gel-based method. Energy-dispersed X-ray spectrometry (EDS) analysis was used to estimate the dopant concentrations. The average crystallite sizes and particle size were estimated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Both studies showed a gradual decrease in the size of the crystallites and particles for x>0.01. Cr can substitute for Ce in the crystal lattice, and the Raman measurements indicated that structural defects in the samples increased as a function of the Cr content in the CeO₂ crystal lattice. The surface topography, examined by scanning electron microscopy (SEM), showed that the undoped sample has a porous and loosely organized structure, whereas the Cr-doped samples exhibited a dense and compact structure. Magnetic measurements of the Ce_1−xCr_xO_2−δ samples at 27 ^oC showed a maximum remanent magnetization value of 0.01 emu/g for x=0.05. The nature and enhancement of room-temperature ferromagnetism was interpreted by taking into account the exchange interaction between Cr³⁺ ions and oxygen vacancies in CeO₂.     

Synthesis and characterization of Cr doped CdS nanoparticles stabilized with polyvinylpyrrolidone

Undoped and Cr (2 and 4 at.%) doped CdS nanoparticles were synthesized in aqueous solution by simple chemical co-precipitation method using polyvinylpyrrolidone (PVP) as stabilizer. The prepared nanoparticles were examined using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). XRD pattern of the nanoparticles showed cubic zincblende phase with the particle size of the order of 3-4 nm, which was in good agreement with the results obtained from TEM studies. The EDAX analysis confirmed that Cd, Cr and S elements were present in the samples and the variations between the target and actual compositions were microscopic. UV-vis DRS spectra of the samples exhibited decrease in the band gap which further attests the incorporation of Cr into CdS nanoparticles. FTIR studies revealed that the undoped as well as Cr doped CdS nanoparticles were capped by polyvinylpyrrolidone.     

Surfactant assisted surface studies of zinc sulfide nanoparticles

We report a simple soft chemical method for the synthesis of ZnS nanoparticles using varying concentration of cationic surfactant CTAB and examine its surface properties. Powder X-ray diffraction, UV-vis spectroscopy, photoluminescence spectroscopy, selective area electron diffraction, and transmission electron microscopy are used to characterize the as prepared ZnS nanoparticles. XRD and TEM measurements show the size of polydispersed ZnS nanoparticles is in the range of 2-5 nm with cubic phase structure. The photoluminescence spectrum of ZnS nanoparticles exhibits four fluorescence emission peaks centered at 387 nm, 412 nm, 489 nm and 528 nm showing the application potential for the optical devices. In Raman spectra of ZnS nanoparticles, the modes around 320, 615 and 700 cm⁻¹ are observed.     

Band gap narrowing and fluorescence properties of nickel doped SnO2 nanoparticles

Nickel-doped tin oxide nanoparticles (sub-5 nm size) with intense fluorescence emission behavior have been synthesized by sol-gel route. The structural and compositional analysis has been carried out by using XRD, TEM, FESEM and EDAX. The optical absorbance spectra indicate a band gap narrowing effect and it was found to increase with the increase in nickel concentration. The band gap narrowing at low dopant concentration (<5%) can be assigned to SnO₂−SnO_2−x alloying effect and for higher doping it may be due to the formation of defect sub-bands below the conduction band.     

Recent developments in the formation and structure of tin-iron oxides by laser pyrolysis

Complex oxides demonstrate specific electric and magnetic properties which make them suitable for a wide variety of applications, including dilute magnetic semiconductors for spin electronics. A tin-iron oxide Sn_1−xFe_xO₂ nanoparticulate material has been successfully synthesized by using the laser pyrolysis of tetramethyl tin-iron pentacarbonyl-air mixtures. Fe doping of SnO₂ nanoparticles has been varied systematically in the 3-10 at% range. As determined by EDAX, the Fe/Sn ratio (in at%) in powders varied between 0.14 and 0.64. XRD studies of Sn_1−xFe_xO₂ nanoscale powders, revealed only structurally modified SnO₂ due to the incorporation of Fe into the lattice mainly by substitutional changes. The substitution of Fe³⁺ in the Sn⁴⁺ positions (Fe³⁺ has smaller ionic radius as compared to the ionic radius of 0.69 Å for Sn⁴⁺) with the formation of a mixed oxide Sn_1−xFe_xO₂ is suggested. A lattice contraction consistent with the determined Fe/Sn atomic ratios was observed. The nanoparticle size decreases with the Fe doping (about 7 nm for the highest Fe content). Temperature dependent ⁵⁷Fe Mössbauer spectroscopy data point to the additional presence of defected Fe³⁺-based oxide nanoclusters with blocking temperatures below 60 K. A new Fe phase presenting magnetic order at substantially higher temperatures was evidenced and assigned to a new type of magnetism relating to the dispersed Fe ions into the SnO₂ matrix.     

Structural and magnetic investigations of sub-nano Mn-Mg ferrite prepared by wet method

Manganese-magnesium ferrite nanoparticles Mn_1−xMg_xFe₂O₄; 0≤x≤0.25 were prepared by the co-precipitation route. The samples were characterized by X-ray diffraction (XRD), which confirms the single phase spinel structure. Crystallite size, calculated from the (3 1 1) peak using the Scherrer formula, was found to increase with increasing Mg²⁺ concentrations and was found to be within the range 3-6 nm. TEM was also used to characterize the microstructure of nanosized Mn_1−xMg_xFe₂O₄. Nominal composition of the samples was determined by Atomic Absorption analysis (AA). Hysteresis loops of manganese-magnesium ferrite were obtained at room temperature and revealed lower saturation magnetization values associated with nanocrystalline Mn_1−xMg_xFe₂O₄ particles. This behavior was attributed to structural distortion of surface spins compared to that of the bulk one.     

Synthesis and investigation of nonlinear optical properties of semiconductor ZnS nanoparticles

ZnS nanoparticles were prepared by a simple chemical method and using PVP (poly vinylpyrrolidone) as capping agent. The sample was characterized by UV-vis spectrophotometer, X-ray diffraction (XRD) and Z-scan technique. XRD pattern showed that the ZnS nanoparticles had zinc blende structure with an average size of about 2.18 nm. The value of band gap of these nanoparticles was measured to be 4.20 eV. The nonlinear optical properties of ZnS nanoparticles in aqueous solution were studied by Z-scan technique using CW He-Ne laser at 632.8 nm. The nonlinear absorption coefficient (β) was estimated to be as high as 3.2×10⁻³ cm/W and the nonlinear refractive index (n₂) was in order of 10⁻⁸ cm²/W. The sign of the nonlinear refractive index obtained negative that indicated this material exhibits self-defocusing optical nonlinearity.     

Structural and magnetic properties of MnxCo1−xFe2O4 ferrite nanoparticles

We report on the structural and magnetic properties of nanoparticles of Mn_xCo_1−xFe₂O₄ (x=0.1, 0.5) ferrites produced by the glycothermal reaction. From the analysis of XRD spectra and TEM micrographs, particle sizes of the samples have been found to be about 8 nm (for x=0.1) and 13 nm (for x=0.5). The samples were characterized by DC magnetization in the temperature range 5-380 K and in magnetic fields of up to 40 kOe using a SQUID magnetometer. Mössbauer spectroscopy results show that the sample with higher Mn content has enhanced hyperfine fields after thermal annealing at 700 °C. There is a corresponding small reduction in hyperfine fields for the sample with lower Mn content. The variations of saturation magnetization, remnant magnetization and coercive fields as functions of temperature are also presented. Our results show evidence of superparamagnetic behaviour associated with the nanosized particles. Particle sizes appear to be critical in explaining the observed properties.     

Structural and magnetic studies on transition metal (Mn, Co) doped ZnO nanoparticles

We report on the structural and magnetic properties of the nanocrystalline samples of Zn_1−x(TM)_xO (TM=Mn, Co and x=0.02, 0.05, 0.10) synthesized by chemical vapor deposition (CVD) method using different carrier gases i.e., Argon (Ar), Oxygen (O₂) and Nitrogen (N₂). X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies reveal wurtzite structure of pure ZnO in all the samples and particle sizes in the range of 15-40 nm. No evidence of any secondary phases having room temperature ferromagnetic behavior has been observed through XRD and TEM studies. Magnetic measurements reveal presence of mixed magnetic phases in the samples, which may be the reason for the low saturation magnetization in the nanoparticles.     

Synthesis of high quality and monodisperse CdS:Mn/ZnS and CdS:Mn/CdS core–shell nanoparticles

CdS:Mn²⁺/ZnS and CdS:Mn²⁺/CdS core–shell nanoparticles were synthesized in aqueous medium via chemical precipitation method in an ambient atmosphere. Polyvinylpyrrolidone (PVP) was used as a capping agent. The effect of the shell (ZnS and CdS) thickness on CdS:Mn²⁺ nanoparticles was investigated. Inorganically passivated core/shell nanocrystals having a core (CdS:Mn²⁺) diameter of 4 nm and a ZnS-shell thickness of ∼0.5 nm exhibited improved PL intensity. Optimum concentration of doping ions (Mn²⁺) was selected through optical study. For all the core–shell samples two emission peaks were observed, the first one is band edge emission in the lower wavelength side due to energy transfer to the Mn²⁺ ions in the crystal lattice; the second emission is characteristic peak of Mn²⁺ ions (⁴T₁ → ⁶A₁). The XRD, TEM and PL results showed that the synthesized core–shell particles were of high quality and monodisperse.     

Preparation and characteristics of Sb-doped LiNiO2 cathode materials for Li-ion batteries

Compounds LiNi_1−xSb_xO₂ (x=0, 0.1, 0.15, 0.2, 0.25) were synthesized by the two-step calcination method. The structural and morphological properties of the products were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis confirms that the uniform solid solution has been formed in the as-prepared compounds without any impurities. It is shown that the crystal lattice parameters (a, c) of the Sb-doped compounds are bigger than those of pure LiNiO₂ and the Sb-doped compound with x=0.2 consists of spherical-like nanoparticles with a mean grain size of 50 nm. The electrochemical performances of as-prepared samples were studied via galvanostatic charge-discharge cycling tests. The compound with x=0.2 exhibits excellent capacity retention during the charge-discharge processes due to its reinforced structural stability, and a discharge capacity of 102.4 mAh/g is still obtained in the voltage range of 2.5-4.5 V after 20 cycles. Thermal analysis further confirms that the structural stability of LiNi_0.8Sb_0.2O₂ is superior to that of pure LiNiO₂.     

Synthesis, characterization and optical properties of water-soluble ZnS:Mn nanoparticles

ZnS nanoparticles with Mn²⁺ doping (0.5-20%) have been prepared through a simple chemical method, namely the chemical precipitation method. The structure of the nanoparticles has been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV-vis spectrometer. The size of the particles is found to be 3-5 nm range. Photoluminescence spectra were recorded for undoped ZnS nanoparticles using an excitation wavelength of 320 nm, exhibiting an emission peak centered at around 445 nm. However, from the Mn²⁺-doped samples, a yellow-orange emission from the Mn²⁺⁴T₁-⁶A₁ transition is observed along with the blue emission. The prepared Mn²⁺-doped sample shows efficient emission of yellow-orange light with the peak emission 580 nm with the blue emission suppressed. The maximum PL intensity is observed only at the excitation energy of 3.88 eV (320 nm). Increase in stabilizing time up to 48 h in de-ionized water yields the enhancement of emission intensity of doped (4% Mn²⁺) ZnS. The correlation made through the concentration of Mn²⁺ versus PL intensity resulted in opposite trend (mirror image) of blue and yellow emissions.     

Optical and ESR studies on Fe doped ZnS nanocrystals

Zn_1 − xFe_xS (x=0.0, 0.1, 0.2, 0.4 and 0.6) nanocrystals have been obtained by chemical co-precipitation from homogeneous solutions of zinc and iron salt compounds, with S²⁻ as precipitating anion formed by decomposition of thiophenol. The TEM micrographs show a spherical shape for ZnS nanocrystals and their average size is around 7 nm. The optical absorption spectra indicate a blue shift of the absorption edge with increasing Fe-content. The luminescence of nanoparticles excite at about 370 nm with an emission peak at around 490 nm. At room temperature, ESR signal characteristic of Fe³⁺ was observed in samples of all concentrations.     

Effect of aluminium doping and annealing on structural and optical properties of cerium oxide nanocrystals

Nanocrystalline fluorite-like structures of Ce_1−xAl_xO_2−δ compounds were prepared by the chemical precipitation method using cerium chloride and aluminium chloride as precursors. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). The effects of aluminium doping concentration and annealing on particle size, lattice parameter and band gap energies were investigated. The particle size of Al-doped CeO₂ samples were found to decrease with Al concentration and it increases from 6 to 20 nm as annealing temperature increases to 900 °C.