Preparation, characterization and study of optical properties of ZnS nanophosphor

In this work the preparation, characterization and photoluminescence studies of pure and copper-doped ZnS nanophosphors are reported, which are prepared by using solid-state reaction technique at a temperature of 100 °C. The as-obtained samples were characterized by X-ray diffraction (XRD) and UV-VIS Reflectance spectroscopy. The XRD analysis confirms the formation of cubic phase of undoped as well as Cu²⁺-doped ZnS nanoparticles. Furthermore it shows that the average size of pure as well as copper-doped samples ranges from 15 to 50 nm. The room-temperature PL spectra of the undoped ZnS sample showed two main peaks centered at around 421 and 450 nm, which are the characteristic emissions of interstitial zinc and sulfur vacancies, respectively. The PL of the doped sample showed a broad-band emission spectrum centered at 465 nm accompanied with shoulders at around 425, 450 and 510 nm, which are the characteristic emission peaks of interstitial zinc, sulfur vacancies and Cu²⁺ ions, respectively. Our experimental results indicate that the PL spectrum confirms the presence of Cu²⁺ ions in the ZnS nanoparticles as expected.     

Synthesis and characterization of Cu doped ZnS nanoparticles using TOPO and SHMP as capping agents

Undoped and Cu²⁺ doped (0.2-0.8%) ZnS nanoparticles have been synthesized through chemical precipitation method. Tri-n-octylphosphine oxide (TOPO) and sodium hexametaphosphate (SHMP) were used as capping agents. The synthesized nanoparticles have been analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrometer, photoluminescence (PL) and thermo gravimetric-differential scanning calorimetry (TG-DTA) analysis. The size of the particles is found to be 4-6 nm range. Photoluminescence spectra were recorded for ZnS:Cu²⁺ under the excitation wavelength of 320 nm. The prepared Cu²⁺-doped sample shows efficient PL emission in 470-525 nm region. The capped ZnS:Cu emission intensity is enhanced than the uncapped particles. The doping ions were identified by electron spin resonance (ESR) spectrometer. The phase changes were observed in different temperatures.     

Synthesis and photoluminescent and nonlinear optical properties of manganese doped ZnS nanoparticles

In this work we synthesized ZnS:Mn²⁺ nanoparticles by chemical method using PVP (polyvinylpyrrolidone) as a capping agent in aqueous solution. The structure and optical properties of the resultant product were characterized using UV-vis optical spectroscopy, X-ray diffraction (XRD), photoluminescence (PL) and z-scan techniques. UV-vis spectra for all samples showed an excitonic peak at around 292 nm, indicating that concentration of Mn²⁺ ions does not alter the band gap of nanoparticles. XRD patterns showed that the ZnS:Mn²⁺ nanoparticles have zinc blende structure with the average crystalline sizes of about 2 nm. The room temperature photoluminescence (PL) spectrum of ZnS:Mn²⁺ exhibited an orange-red emission at 594 nm due to the ⁴T₁-⁶A₁ transition in Mn²⁺. The PL intensity increased with increase in the Mn²⁺ ion concentration. The second-order nonlinear optical properties of nanoparticles were studied using a continuous-wave (CW) He-Ne laser by z-scan technique. The nonlinear refractive indices of nanoparticles were in the order of 10⁻⁸ cm²/W with negative sign and the nonlinear absorption indices of these nanoparticles were obtained to be about 10⁻³ cm/W with positive sign.     

Mechano-chemical synthesis and optical properties of ZnS nanoparticles

In the present work, we report the synthesis and optical properties of ZnS nanoparticles produced by the mechano-chemical route. We used zinc acetate and sodium sulphide as source materials in a high energy planetary ball mill at rotation speed of 300 rpm and vial rotation speed of 600 rpm with ball to powder (BPR or charge ratio CR) 5:1 for 30 and 90 min. The milled powders were washed with methanol to remove impurity and dried at 300 °C for 1 h. The prepared nanoparticles have been characterized using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), UV–vis–NIR spectrophotometer and Fluorescence spectroscopy. The crystallite size of the synthesized ZnS nanoparticles is found to be in the range 7–8 nm which was calculated using Debye–Scherer's formula. The value of optical band gap has been found to be in the range 3.80–4.15 eV. Room temperature photoluminescence (PL) spectrum of ZnS samples exhibit a blue emission peaked at 466 nm under UV excitation.     

Characterization and luminescent properties of SiO2:ZnS:Mn and ZnS:Mn nanophosphors synthesized by a sol-gel method

ZnS and SiO₂-ZnS nanophosphors, with or without different concentration of Mn²⁺ activator ions, were synthesized by using a sol-gel method. Dried gels were annealed at 600 °C for 2 h. Structure, morphology and particle sizes of the samples were determined by using X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The diffraction peaks associated with the zincblende and the wurtzite structures of ZnS were detected from as prepared ZnS powders and additional diffraction peaks associated with ZnO were detected from the annealed powders. The particle sizes of the ZnS powders were shown to increase from 3 to 50 nm when the powders were annealed at 600 °C. An UV-Vis spectrophotometer and a 325 nm He-Cd laser were used to investigate luminescent properties of the samples in air at room temperature. The bandgap of ZnS nanoparticles estimated from the UV-Vis data was 4.1 eV. Enhanced orange photoluminescence (PL) associated with ⁴T₁→⁶A₁ transitions of Mn²⁺ was observed from as prepared ZnS:Mn²⁺and SiO₂-ZnS:Mn²⁺ powders at 600 nm when the concentration of Mn²⁺ was varied from 2-20 mol%. This emission was suppressed when the powders were annealed at 600 °C resulting in two emission peaks at 450 and 560 nm, which can be ascribed to defects emission in SiO₂ and ZnO respectively. The mechanism of light emission from Mn²⁺, the effect of varying the concentration on the PL intensity, and the effect of annealing are discussed.     

Synthesis and optical characterization of PVP and SHMP-encapsulated Mn-doped ZnS nanocrystals

Zinc sulfide semiconductor nanocrystals doped Mn²⁺ have been synthesized via a solution-based method utilizing optimum dopant concentration (4%) and employing polyvinyl pyrrolidone (PVP) and sodium hexametapolyphosphate (SHMP) as capping agents. UV-vis absorbance spectra for all of the synthesized nanocrystals show an exitonic peak at around 310 nm. The particle size and morphology were characterized by scanning electron microscopy (SEM), FT-IR, X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectrum (PL). Diffraction data confirmed that the crystallite size is around 3-5 nm. Room temperature photoluminescence (PL) spectrum for the bare ZnS sample shows a strong band at ∼445 nm. The uncapped and capped(SHMP, PVP) ZnS:Mn²⁺ samples show a strong and broad band in the ∼580-585 nm range.     

Hydrothermal synthesis and characterization of ZnS hierarchical microspheres

In the present work, wurtzite ZnS hierarchical microsphere nanostructures composed of nanowires were synthesized through hydrothermal method. The morphologies and microstructures of the as obtained wurtzite ZnS sample were investigated by scanning electron microscopy and transmission electron microscopy. The results show that the diameter of the nanowires is about 10 nm, the length is about 500 nm, growing along the [0 0 1] direction. UV–visible spectroscopy shows that the band gap of the as obtained ZnS hierarchical microspheres is 3.4 eV. Room temperature photoluminescence measurements reveals a strong green emission peak at around 516 nm. The N₂ adsorption–desorption isotherms experiment at 77 K exhibits that the surface area of the ZnS sample is 99.87 m² g⁻¹.     

Size dependent electron momentum density distribution in ZnS

In this paper, we present size dependent electron momentum density distribution in ZnS. ZnS nanoparticles of size 3.8 nm and 2.4 nm are synthesized using the chemical route and characterized by X-ray diffraction (XRD). The Compton profile measurements are performed on both the nano-sized as well as bulk ZnS samples employing 59.54 keV gamma-rays from ²⁴¹Am source. The results reveal that the valence electron density in momentum space becomes narrower with reduction of particle size. To evaluate the charge transfer on compound formation, the ionic model based calculations for a number of configurations of Zn^+xS^−x (0.0≤x≤2) are also performed utilizing free atom Compton profiles. These results suggest different amounts of charge transfer in these materials varying from 1.2 to 2.0 electron from Zn to S atom.     

Optical properties of annealed Mn-doped ZnS nanoparticles

Cysteine stabilized ZnS and Mn²⁺-doped ZnS nanoparticles were synthesized by a wet chemical route. Using the ZnS:Mn²⁺ nanoparticles as seeds, silica-coated ZnS (ZnS@Si) and ZnS:Mn²⁺ (ZnS:Mn²⁺@Si) nanocomposites were formed in water by hydrolysis and condensation of tetramethoxyorthosilicate (TMOS). The influence of annealing in air, formier gas, and argon at 200-1000 °C on the chemical stability of ZnS@Si and ZnS:Mn²⁺@Si nanoparticles with and without silica shell was examined. Silica-coated nanoparticles showed an improved thermal stability over uncoated particles, which underwent a thermal combustion at 400 °C. The emission of the ZnS@Si and ZnS:Mn²⁺@Si passed through a minimum in photoluminescence intensity when annealed at 600 °C. Upon annealing at higher temperatures, ZnS@Si conserved the typical emission centered at 450 nm (blue). ZnS:Mn²⁺@Si yielded different high intensity emissions when heated to 800 °C depending on the gas employed. Emissions due to the Mn²⁺ at 530 nm (green; Zn₂SiO₄:Mn²⁺), 580 nm (orange; ZnS:Mn²⁺@Si), and 630 nm (red; ZnS:Mn²⁺@Si) were obtained. Therefore, with a single starting product a set of different colors was produced by adjusting the atmosphere wherein the powder is heated.     

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.     

Enhanced visible light emission from Co doped ZnS nanoparticles

ZnS nanoparticles with Co²⁺ doping have been prepared at room temperature through a soft chemical route, namely the chemical co-precipitation method. The nanostructures of the prepared nanoparticles have been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), and UV-vis spectrophotometer. The sizes of as prepared nanoparticles are found to be in 1–4 nm range. Room-temperature photoluminescence (PL) spectrum of the undoped sample exhibits emission in the blue region with multiple peaks under UV excitation. On the other hand, in the Co²⁺ doped ZnS samples enhanced visible light emissions with emission intensities of ~35 times larger than that of the undoped sample are observed under the same UV excitation wavelength of 280 nm.     

Synthesis of nanocrystalline and mesoporous zinc sulphide from a single precursor Zn(SOCCH3)2Lut2 complex

We report the formation of mesoporous zinc sulphide, composed by the fine network of nanoparticles, which was formed via a single precursor Zn(SOCCH₃)₂Lut₂ complex. The complex was chemically synthesized using zinc carbonate basic, 3,5-lutidine and thioacetic acid, in air. The metal precursor complex was characterized using different conventional techniques. Thermogravimetric analysis (TGA) result indicates that the decomposition of the complex starts at 100 °C and continues up to 450 °C, finally yielding ZnS. ZnS nanocrystals were characterized by powder X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), N₂-sorption isotherm, UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The grain diameter of nanocrystals was found to be 4-5 nm. The material followed Type-IV N₂-sorption isotherm, which is the characteristic of mesoporous materials. The band gap energy, as obtained from optical measurements was around 3.8 eV.     

Synthesis of Mn-doped ZnS architectures in ternary solution and their optical properties

Mn-doped ZnS sea urchin-like architectures were fabricated by a one-pot solvothermal route in a ternary solution made of ethylenediamine, ethanolamine and distilled water. The as-prepared products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and photoluminescence spectra (PL). It was demonstrated that the as-prepared sea urchin-like architectures with diameter of 0.5-1.5 μm were composed of nanorods, possessing a wurtzite structures. The preferred growth orientation of nanorods was found to be the [0 0 2] direction. The PL spectra of the Mn-doped ZnS sea urchin-like architectures show a strong orange emission at 587 nm, indicating the successful doping of Mn²⁺ ions into ZnS host. Ethanolamine played the role of oriented-assembly agent in the formation of sea urchin-like architectures. A possible growth mechanism was proposed to explain the formation of sea urchin-like architectures.     

Optical measurements of ZnS nanoparticles aqueous solution

We synthesized zinc sulfide (ZnS) nanopowders with size ranging from 2 to 100 nm by a simple, low-cost, and mass production chemical method. The nanoparticles (NPs) were characterized by X-ray powder diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), and UV-vis absorption spectroscopy. Our study concerns also the change in the refractive index of deionized water in presence of ZnS nanospheres. We present experimental results on effective index variation of water dispersed ZnS NPs at different wavelengths in visible spectrum.     

Characterization of ZnS nanoparticles synthesized by co-precipitation method

ZnS nanoparticles are prepared by homogeneous chemical co-precipitation method using EDTA as a stabilizer and capping agent. The structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible(UV-Vis)absorption, and photoluminescence spectroscopy. The x-ray diffraction pattern exhibits a zinc-blended crystal structure at room temperature. The average particle size of the nanoparticles from the scanning electron microscopy image is about50 nm. The ultraviolet absorption spectrum shows the blue shift in the band gap due to the quantum confinement effect.The photoluminescence spectrum of Zn S nanoparticles shows a blue visible spectrum.     

Photoluminescent zinc oxide polymer nanocomposites fabricated using picosecond laser ablation in an organic solvent

Nanocomposites made of ZnO nanoparticles dispersed in thermoplastic polyurethane were synthesized using picosecond laser ablation of zinc in a polymer-doped solution of tetrahydrofuran. The pre-added polymer stabilizes the ZnO nanoparticles in situ during laser ablation by forming a polymer shell around the nanoparticles. This close-contact polymer shell has a layer thickness up to 30 nm. Analysis of ZnO polyurethane nanocomposites using optical spectroscopy, high resolution transmission electron microscopy and X-ray diffraction revealed that oxidized and crystalline ZnO nanoparticles were produced. Those nanocomposites showed a green photoluminescence emission centred at 538 nm after excitation at 350 nm, which should be attributed to oxygen defects generated during the laser formation mechanism of the monocrystalline nanoparticles. Further, the influence of pulse energy and polymer concentration on the production rate, laser fluence and energy-specific mass productivity was investigated.     

Photoluminescence of Cu-doped and Cu-doped ZnS nanocrystallites

ZnS:Cu⁺ and ZnS:Cu²⁺ nanocrystallites have been obtained by chemical precipitation from homogeneous solutions of zinc, copper salt compounds, with S²⁻ as precipitating anion formed by decomposition of thioacetamide. X-ray diffraction (XRD) analysis shows that average diameter of particles is about 2.0-2.5 nm. The nanoparticles can be doped with copper during synthesis without altering XRD pattern. However, the emission spectrum of ZnS nanocrystallites doped with Cu⁺ and Cu²⁺ consists of two emission peaks. One is at 450 nm and the other is at 530 nm. The absorptive spectrum of the doped sample is different from that of un-doped ZnS nanoparticles. Because the emission process of the Cu⁺ luminescence center in ZnS nanocrystallites is remarkably different from that of the Cu²⁺ luminescence center, the emission spectra of Cu⁺-doped samples are different from those of Cu²⁺-doped samples.     

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.     

Synthesis, effect of capping agents, structural, optical and photoluminescence properties of ZnO nanoparticles

Zinc oxide nanoparticles were synthesized using chemical method in alcohol base. During synthesis three capping agents, i.e. triethanolamine (TEA), oleic acid and thioglycerol, were used and the effect of concentrations was analyzed for their effectiveness in limiting the particle growth. Thermal stability of ZnO nanoparticles prepared using TEA, oleic acid and thioglycerol capping agents, was studied using thermogravimetric analyzer (TGA). ZnO nanoparticles capped with TEA showed maximum weight loss. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for structural and morphological characterization of ZnO nanoparticles. Particle size was evaluated using effective mass approximation method from UV-vis spectroscopy and Scherrer's formula from XRD patterns. XRD analysis revealed single crystal ZnO nanoparticles of size 12-20 nm in case of TEA capping. TEA, oleic acid and thioglycerol capped synthesized ZnO nanoparticles were investigated at room temperature photoluminescence for three excitation wavelengths i.e. 304, 322 and 325 nm, showing strong peaks at about 471 nm when excited at 322 and 325 nm whereas strong peak was observed at 411 for 304 nm excitation.     

Photoluminescence of CdS nanoparticles embedded in a starch matrix

CdS nanoparticles were synthesized by precipitation in aqueous solution using starch as the capping molecule, and the effect of the pH of the solution on the optical absorption, photoluminescence, and size of the nanoparticles was studied. Absorption spectra, obtained by photoacoustic spectroscopy, indicated that the band gap energy of the crystalline nanoparticles decreased from 2.68 eV down to 2.48 eV by increasing the pH of the solution from 9 up to 14. The X-ray diffraction analysis revealed that the CdS nanoparticles were of zinc blende structure, and that the particle size increased from 1.35 nm up to 2.45 nm with increasing pH. In addition, temperature-dependent photoluminescence (PL) measurements of the capped material showed a blue-shift of the emission peak for temperatures higher than 150 K, indicating the influence of starch on the formation of defect levels on the surface of the CdS nanoparticles.