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1.
CdS and CdS/ZnS core-shell structure nano particles were synthesized in micro emulsion, and characterized by X-ray diffraction(XRD), transmission electron microscopy (TEM), UV absorption spectra and PL. The average diameter of CdS was about 3.3 nm, and CdS/ZnS core-shell structure was confirmed by XRD and UV. Considering the optical properties of CdS/ZnS core-shell structure nanoparticles which have different ZnS shell thickness, the UV absorption edge of CdS/ZnS becomes as lightred-shift with the thickness of ZnS layer increasing, and the absorption of shortwave band is strongly enhanced at the same time. The PL spectra indicate that ZnS shell layer can greatly eliminate surface defects of CdS nanoparticles and make its band-edge directed recombination increased, and the luminous efficiency of CdS is improved greatly when it has appropriate shell thickness. 相似文献
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Yang H Holloway PH Cunningham G Schanze KS 《The Journal of chemical physics》2004,121(20):10233-10240
Synthesis and characterization of highly luminescent ZnS-passivated CdS:Mn (CdS:Mn/ZnS) core/shell structured nanocrystals are reported. Mn-doped CdS core nanocrystals are produced ranging from 1.5 to 2.3 nm in diameter with epitaxial ZnS shell of wider band gap via a reverse micelle process. UV irradiation-stimulated photo-oxidation of the ZnS shell results in formation of sulfate (ZnSO(4)) as determined by x-ray photoelectron spectroscopy, which increases the photoluminescence emission intensity and subsequent photostability. Luminescent relaxation lifetime data present two different decay components, consisting of slow decay emission from the Mn center and a fast decay emission from a defect-related center. The impact of the density of surface defect states upon the emission spectra is discussed. 相似文献
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Optical and Structural Properties of Doped ZnS Nanoparticles Produced by the Sol-Gel Method 总被引:1,自引:0,他引:1
Optical and structural properties of Mn2+-doped ZnS nanoparticles in an organic matrix are experimentally and theoretically studied. The nanoparticles, which were produced by the sol-gel method, are nearly monodisperse with a diameter of approximately 3 nm and show the characteristic orange-red luminescence of Mn2+ centers in a crystalline ZnS matrix. The absorption spectrum of the embedded ZnS nanoparticles is slightly blue shifted and broadened compared to the reference system containing ZnS microparticles. This blue shift is caused by quantum size effects, whereas the broadening is due to defects such as lattice distortions, and vacancies, which are probably located close to the surface in the case of small particles. With increasing temperature the absorption spectra shift to the red and are broadened due to thermal activated diffusion of ions close to the surface. In contrast, the spectral feature of the emission spectra via the Mn2+ center is nearly unchanged compared to the ZnS microparticles. Furthermore, the quantum efficiency is increased and the decay time of the electron-hole pairs is shortened to the nanosecond regime because of the enhanced probability of the electron-hole pairs to see the Mn2+ center. Therefore, the only effect of doping of ZnS nanoparticles with Mn2+ center is the suppression of the relaxation of electron-hole pairs via surface defects generating a highly efficient and fast relaxation of the electron-hole pairs via the Mn2+ center. 相似文献
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A new ZnS/CdS heterojunction is constructed through the direct sulfurization of a metal ions exchanged Zn/Cd-MOF precursor(MOF=metal-organic framework material). The composition, structure, morphology, photo-absorption and photoelectric performance of the ZnS/CdS are characterized by powder X-ray diffraction(PXRD), scanning electron microscope(SEM), transmission electron microscope(TEM), diffuse reflection spectrum(DRS), photoelectric current(PEC), electrochemical impedance spectroscopy(EIS) and photoluminescence(PL) technologies. Since the metal ions are highly orderly separated by the organic ligands and the inherent porosity of the Zn/Cd-MOF, the as-synthesized ZnS/CdS possesses a large surface area and intimate contact at the heterogeneous interface with uniform ZnS/CdS nanoparticles. The photocatalytic hydrogen evolution activity of the ZnS/CdS is investigated under visible light irradiation(λ ≥ 420 nm). It exhibits enhanced photocatalytic performance that the optimal ZnS/CdS achieves a maximum average hydrogen production rate of 2348 μmol·h-1·g-1. A possible electron transfer mechanism is therefore proposed by the analyses of the Mott-Schottky plots. 相似文献
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Bohua Dong Lixin Cao Ge Su Wei Liu Hua Qu Daixun Jiang 《Journal of colloid and interface science》2009,339(1):78-82
Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core–shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core–shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40 nm). Photoluminescence (PL) spectroscopy and UV–vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu2+ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu2+ concentrations as low as 7.3 × 10−9 mol L−1, thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed. 相似文献
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M. Yu. Koroleva E. V. Gulyaeva E. V. Yurtov 《Russian Journal of Inorganic Chemistry》2013,58(9):1034-1039
The effect of synthesis conditions (molar ratio between precursors, concentration of surfactants, synthesis temperature) on the size of CdS, ZnS and Ag2S nanoparticles (NPs) stabilized by sodium bis(2-ethylhexyl)succinate and polyoxyethylenesorbitan monooleate was studied. It was established that stabilization by polyoxyethylenesorbitan results in formation of smaller NPs (~8 nm) as compared to that in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (14–60 nm), which is due to the difference between the adsorption rates of these surfactants onto the surface of synthesized NPs. The resulting aqueous dispersions of CdS, ZnS and Ag2S NPs exhibit long-term stability to sedimentation. The nanoparticle size increases insignificantly with temperature increasing to 65–70°C and rises abruptly at higher temperatures. The increase in the ratio between concentrations of precursors (sulfide and metal ions) also results in an increase in NP size, allowing one to synthesize nanoparticles of prescribed sizes. The optical properties of the resulting nanoparticles were studied. The positions of the exciton peaks and the luminescence intensity peaks of the dispersions of synthesized CdS and ZnS NPs were determined. 相似文献
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Chen W Aguekian VF Vassiliev N Serov AY Filosofov NG 《The Journal of chemical physics》2005,123(12):124707
A fast decay emission peaking at 645 nm with a decay lifetime within the experimental resolution of 0.14 micros is observed in ZnS:Mn2+ nanoparticles. This short-lived signal is also observed in pure ZnS and MgS: Eu3+ nanoparticles, which has nothing to do with Mn(2+)-doped ions but is from the deep trap states of the host materials. The short-lived component decreases in intensity relative to the Mn2+ emission at higher excitation powers, while it increases in intensity at low temperatures and shifts to longer wavelengths at longer time delays. Our observations demonstrated further that the emission of Mn2+ in ZnS: Mn2+ nanoparticles behaves basically the same as in bulk ZnS: Mn2+; the fast decay component is actually from the intrinsic and defect-related emission in sulfide compounds. 相似文献
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A variety of nearly monodisperse semiconductor nanocrystals, such as CdS, ZnS, and ZnS:Mn, with controllable aspect ratios have been successfully prepared through a facile synthetic process. These as-prepared nanocrystals were obtained from the reactions between metal ions and thioacetamide by employing octadecylamine or oleylamine as the surfactants. The effects of reaction temperature and time, ratios of thioacetamide to inorganic precursors, and the reactant content on the size and crystal purity of the nanorods, have been systematically investigated. The optical properties and the formation mechanism of the nanorods have also been discussed. For the next biolabel applications, these hydrophobic nanocrystals have also been transferred into hydrophilic colloidal spheres by means of an emulsion-based bottom-up self-assembly approach. 相似文献
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Deng Z Tong L Flores M Lin S Cheng JX Yan H Liu Y 《Journal of the American Chemical Society》2011,133(14):5389-5396
We report a simple, fast and green phosphine-free colloidal chemistry to synthesize high-quality wurtzite-type Mn-doped ZnS quantum rods (QRs) with tunable diameters (1.6-5.6 nm), high aspect ratios (up to 50), variable Mn doping levels (0.18-1.60%), and high quantum yields (up to 45%). The electron paramagnetic resonance spectra with modeling reveal the successful doping of paramagnetic Mn(2+) ions in the host ZnS QRs. The Mn-doped ZnS QRs demonstrate tunable dual-color (orange and blue) emissions by tuning the doping levels and UV excitation wavelengths. The orange emission with long decay lifetime (3.3 ms) originates from the doped Mn(2+) states, while the blue emission with fast decay lifetime (0.31 ns) is attributed to the QR surface states. The bright two- and three-photon excitation upconversion luminescence from the Mn-doped ZnS QRs have been observed using tunable near-infrared femtosecond laser. Our strategy provides a versatile route to programmably control the optical properties of anisotropic semiconductor nanomaterials, which may create new opportunities for photonic devices and bioimaging applications. 相似文献
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Pure and Mn-doped NaTaO3 nanoparticles were synthesized by a simple hydro- thermal method. XRD and XPS results suggested that manganese ions were successfully doped into the NaTaO3 crystalline in Mn2+ state. UV-vis diffuse reflectance spectra revealed the obvious red-shift in the series of manganese doped NaTaO3 nanoparticles, resulting in a decrease in the band gap of NaTaO3 with the increase of Mn2+ doping concentration. The photo-degradation experiment indicated that manganese doped NaTaO3 showed good photocatalytic performance and methylene blue(MB) degradation is improved with lower doping concentration of manganese ions under visible light. The simulation of energy band structure by density functional theory unfolded that the substitution of Ta5+ ions by Mn2+ ions resulted in an intermediate band(IB) below the bottom of the conduction band(CB), which was mainly attributed to the state of Mn 3d. 相似文献
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《Spectrochimica Acta Part B: Atomic Spectroscopy》1999,54(1):133-141
The fluorescence XAFS (X–ray absorption fine structure) technique using synchrotron radiation was applied to characterize zinc in the Hg–Zn, Cd–Zn, and Bi–Zn coprecipitates, and to elucidate the reaction mechanism of the coprecipitation of zinc from a strong acidic solution. Hg LII–, Cd K–, and Bi LIII–edge XAFS spectra suggested that the respective host materials of the coprecipitates listed above are metacinnabar (HgS), greenockite (CdS), and bismuthinite (Bi2S3) and that existence of zinc has not affected the local structure of the host metal sulfides in each system. On the other hand, the Zn K–edge XAFS spectra of each coprecipitate indicated that the chemical forms of zinc compounds are controlled by the crystal structure of the host sulfides.The shapes of the Zn K–XAFS spectra of the Hg–Zn and Cd–Zn coprecipitates showed a strong resemblance to those of crystalline standards ZnS, wurtzite and spharelite. It was suggested that the two coprecipitated phases (HgS, ZnS) and (CdS, ZnS) may form a solid solution in the Hg–Zn and Cd–Zn coprecipitates. The local structure around the zinc(II) ion in the Bi–Zn coprecipitate is the same as that around hexaaqua–zinc(II) ions, and adsorption of soluble ions or mechanical occlusion from the mother liquor is regarded as a driving force of coprecipitation in the Bi–Zn system. 相似文献
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CdS:Cu nanoparticles were successfully synthesized by a coprecipitation method using mercaptoethanol as a capping agent. Thermoluminescence (TL) spectra of CdS:Cu nanoparticles were studied for different exposure time. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectrometry. XRD and SEM measurements showed that the size of the crystallites was in the range 8–17 nm. Optical measurements indicated a blue-shift in the absorption band edge upon Cu doping. The direct allowed bandgap of undoped and Cu-doped CdS nanoparticles was 2.53 and 2.64 eV, respectively. We also calculated the kinetic parameters for Cu-doped CdS nanoparticles from the TL glow curves measured at 254, 249, and 244 °C with variation of the ultra-violet (UV) exposure time. The glow curve shows general order kinetics, and its kinetic parameters are calculated. 相似文献
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Here, we report the role of dopant concentration and surface coating of CdS: Eu3+ nanocrystals on the modification of crystal structure and their photoluminescence properties by steady-state and time resolved fluorescence studies. It is found that photoluminescence properties are sensitive to the crystal structure which is controlled by surface coating and dopant concentration. The emission intensity of the peak at 614 nm (5D0 --> 7F2) of the Eu3+-ions is found to be sensitive to the doping and surface coating of CdS nanocrystals. It is found that the average decay times tau are 248, 353 and 499 micros for 0.25, 0.5 and 1.0 mol% Eu ions doped into CdS nanocrystals, respectively. From the decay time measurements, it is evident that the energy transfer occurs from CdS nanoparticles to Eu3+ ions and the calculated energy transfer efficiency from CdS nanoparticles to Eu3+ ions is 9.2 and 35% for Eu3+ ions coated and doped CdS nanoparticles, respectively. Our analysis suggests that site symmetry of ions plays a very important role in the modifications of radiative and nonradiative relaxation mechanisms. 相似文献
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本文在AOT/异辛烷反胶束中合成了CdS和ZnS半导体纳米粒子。粒子的荧光量子产率随胶束水含量的增大而减小。这可以归结为水含量增大导致胶粒表面Cd2+或Zn2+离子浓度降低,因为这两种离子在胶粒表面富集有利于形成硫空位,从而增大光生电子-空穴对的发光复合。研究发现,Ag+离子可以有效猝灭CdS和ZnS纳米粒子的荧光发射,该猝灭过程可以用Ag+离子在胶束中的Poisson分布来描述。以溶解在有机相中的pyrene作电子给体,在光激发下可以向CdS粒子注入电子,而和ZnS粒子间没有电荷转移发生,这可以解释为两种半导体的导带边相对于pyrene激发态氧化电位所处的位置不同。Cu2+或Ag+离子在ZnS颗粒表面吸附,可以形成CuxZn1-xS或Ag2xZn1-xS复合粒子,降低ZnS粒子的导带位置,从而使之能够接受来自pyrene激发态的电子。实验结果证实了这种论点。 相似文献
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Extraordinary Changes in the Electronic Structure and Properties of CdS and ZnS by Anionic Substitution: Cosubstitution of P and Cl in Place of S
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Summayya Kouser S. R. Lingampalli Dr. P. Chithaiah Anand Roy Sujoy Saha Prof. Umesh V. Waghmare Prof. C. N. R. Rao 《Angewandte Chemie (International ed. in English)》2015,54(28):8149-8153
Unlike cation substitution, anion substitution in inorganic materials such as metal oxides and sulfides would be expected to bring about major changes in the electronic structure and properties. In order to explore this important aspect, we have carried out first‐principles DFT calculations to determine the effects of substitution of P and Cl on the properties of CdS and ZnS in hexagonal and cubic structures and show that a sub‐band of the trivalent phosphorus with strong bonding with the cation appears in the gap just above the valence band, causing a reduction in the gap and enhancement of dielectric properties. Experimentally, it has been possible to substitute P and Cl in hexagonal CdS and ZnS. The doping reduces the band gap significantly as predicted by theory. A similar decrease in the band gap is observed in N and F co‐substituted in cubic ZnS. Such anionic substitution helps to improve hydrogen evolution from CdS semiconductor structures and may give rise to other applications as well. 相似文献
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Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts. 相似文献
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ZnS/CdS/ZnS quantum dot quantum well was prepared. The optical properties of ZnS/CdS/ZnS QDQW with different thickness of CdS well and ZnS shell were studied. Absorption spectra, emission spectra, and luminescence lifetimes were measured. The observed luminescence was assigned to the bulk donor-acceptor pair recombination of CdS and can be enhanced by increasing the thickness of the CdS well or coating an appropriate thickness of ZnS shell on the surface of the CdS well. The luminescence enhancement was caused by the relative reduce in the surface effect. The luminescence lifetimes were influenced strongly by the surface state. 相似文献