Synthesis and morphological control of europium doped cadmium sulphide nanocrystals

Europium doped cadmium sulphide (Cd(0.98)Eu(0.2)S) nanostructures were synthesised by chemical co-precipitation method using ethylene glycol (EG) and deionized water (Eu:CdS-1), and isopropyl alcohol (IPA) and deionized water (Eu:CdS-2) as mixed solvents. It has been found that the nanostructure of the europium doped CdS can be controlled by simply varying the mixed solvent system. Powder XRD pattern reveals the formation of hexagonal (wurtzite) and cubic (zinc blende) structure for Eu:CdS-1, and Eu:CdS-2, respectively. The crystallite size of the sample prepared using IPA and deionized water was measured to be 2.64 nm which is much smaller than that of the sample prepared using EG and deionized water as mixed solvent (3.65 nm). Morphology of the materials can also be changed from flower shaped crystals to paddy like structures by varying the mixed solvents. Band gap values of Eu3+ doped CdS nanocrystals synthesized from two different solvents were estimated using UV-reflectance spectra. The size and crystallinity of the samples were confirmed by HRTEM and SAED analysis. A significant change in the PL emission of the CdS nanocrystals was observed for the europium doped CdS which is mainly due to the presence of EU3+ ions which also play a significant role in the energy transfer process. It was also observed that the shift in the emission and efficiency depends on size and shape of the synthesised nanoparticles.     

Effects of ethylenediamine to water ratios on cadmium sulfide nanorods and nanoparticles produced by a solvothermal method

Cadmium sulfide nanorods and nanoparticles were successfully produced by a solvothermal reaction at 200 °C for 24 h using ethylenediamine and water as pure and mixed solvents. The products were analyzed by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. In pure ethylenediamine, they show the hexagonal structure CdS nanorods with 0.2-2 μm long and 30 nm diameter, and the 1LO and 2LO modes at 299.36 and 600.72 cm^− 1, respectively. Growth of CdS nanorods is along the [001] direction, interpreted by HRTEM images and SAED patterns. In the 50:50 vol.% of ethylenediamine:water mixed solvents, the length of CdS nanorods decreased to 100-200 nm. The CdS nanoparticles were produced when pure water was used.     

Synthesis and optoelectrochemical properties of ZnS:Mn nanocrystals

Mn2+ ions doped ZnS semiconductor nanocrystals (ZnS:Mn NCs) were synthesized using colloidal chemical method at 70 degrees C without any capping agents. The as-prepared undoped ZnS and ZnS:Mn NCs were characterized by UV-Vis absorption spectra, fluorescent emission spectra, X-ray powder diffraction (XRD), inductively coupled plasma analysis (ICP), X-ray photoelectron spectroscopy (XPS), Dynamic light scattering (DLS), cyclic voltammogram and electronic transmission microscopy (TEM). The dependence of photoluminescence of ZnS:Mn NCs on dopant concentration was studied. The results show that Mn2+ ions mainly stay at ZnS nanocystal surface, and Mn2+-surface defect state complex was formed, as a result of which, surface defect emission of ZnS nanocrystals was substituted with Mn2+-related PL emission. The strongest fluorescent emission intensity was obtain at 1.85 at% Mn2+ doped ZnS:Mn NCs. The Mn2+ doped ZnS:Mn NCs are of 5 nm in diameter. The emission peak at 575 nm is attributed to d-d (4T1 --> 6A1) transition of Mn2+ ions. The existence of Mn2+-related photoluminescence could be well correlated with cyclic voltammogram of Mn2+-doped NCs, where pair of oxidation and reduction peaks were clearly observed due to the doped Mn2+ ions. The adsorbed Mn2+ ions on ZnS NCs produced neither Mn2+ emission nor redox peaks. For heavily doped ZnS:Mn NCs (4.87 at%), redox peaks gap in cyclic voltammogram became larger and new oxidation peak appeared. Correspondingly, when the Mn2+ doping concentration reached 4.87 at%, the Mn2+-related emission totally disappears due to the Mn-Mn interactions. This work implys that electrochemical technique is possibly an useful tool to probe the local structure of doped Mn2+ ions.     

Preparation of lanthanide doped CdS, ZnS quantum dots in natural polysaccharide template and their optical properties

Employing a biomimic method using polysaccharide as template, luminescent lanthanide ions doped CdS and ZnS quantum dots (QDs) were prepared. According to the results of TEM and absorbance, nanocrystals with an average size of 6 nm were formed under mild condition without any toxic and expensive agent applied. Differentiating from the un-doped CdS and ZnS QDs prepared in polysaccharide template, the lanthanide doped QDs exhibited obvious dopant emission in their photoluminescence spectrum. It was also found that the dopant PL became more prominent with increasing lanthanide doping concentration, while the highest PL intensity was obtained at a doping level of 1% for both of CdS and ZnS QDs. When different lanthanide ions were introduced into the CdS QDs in polysaccharide template, varied emission wavelength were able to be obtained. This study provides an easy, mild and environmental friendly alternative method to prepare doped quantum dots. In addition, the bioactivity and processabilities endowed by the polysaccharide template may expand the applications potential of this type of optical materials.     

Luminescence in Mn-doped CdS nanocrystals

We have synthesized Mn-doped CdS nanocrystals (NCs) with size ranging from 1.8–3 nm. Photoluminescence (PL) spectra of the doped NCs differ from that of the undoped NCs with an additional peak due to Mn d-d transitions. Electron paramagnetic resonance spectra along with X-ray absorption spectroscopy and PL spectra confirm the incorporation of Mn in the CdS lattice. The fact that emissions from surface states and the Mn d levels occur at two different energies, allowed us to study the PL lifetime decay behaviour of both kinds of emissions.     

One-dimensional cadmium sulfide (CdS) nanostructures by the solvothermal process: Controlling crystal structure and morphology aided by different solvents

Cadmium sulfide (CdS) nanowires and nanorods with different aspect ratios were successfully synthesized by the solvothermal method aided with various solvents, namely ethylenediamine, ethanolamine and triethylene tetraamine. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses revealed that, highly pure CdS nanostructures were crystallized with different structures and preferable growth orientations depending on solvent nature. Field emission electron microscope (FE-SEM) images showed that the aspect ratio of CdS nanostructures depends upon the dielectric constant and boiling temperature of solvents. CdS nanostructures with the highest aspect ratio in the form of nanowire were obtained using ethylenediamine, whereas CdS nanorods were produced in the presence of ethanolamine and triethylene tetraamine solvents. The absorption edge of CdS nanowires and nanorods showed a blue shift compared with that of bulk CdS due to an increase in their band gap energies.     

ZnO纳米棒Al掺杂和A1,N共掺杂的制备技术与光致发光性能

采用水热法首先合成了Al掺杂ZnO(AZO)纳米棒,在此基础上通过550℃的氨气氛中退火制备了Al,N共掺杂ZnO(ANZ())纳米棒.运用X射线衍射(XRD),场发射扫描电镜(FESEM),透射电子显微镜(TEM),X射线能谱(EDS)和光致发光(PL)对样品进行了表征与分析.结果表明,制备的AZO和ANZ()纳米棒...     

Spectroscopic investigations on hybrid nanocomposites: CdS : Mn nanocrystals in a conjugated polymer

We have used electron paramagnetic resonance (EPR) spectroscopy for investigating the properties of spins, such as those carried by polarons which carry both spin and charge in poly (meta/para phenylene) PMPP: CdS doped Mn based nanocomposites. To identify the nature of paramagnetic species in PMPP matrix, we have studied the effect of different physical parameters. It was found that we are in presence of trapped polarons and localized spins which concentration has been estimated. Moreover, spin–spin and spin–lattice relaxation rates have been calculated. Then, we discussed the results of optical and EPR study on the hybrid nanocomposite (CdS nanostructures, doped with manganese (II) ions, incorporated in PMPP conjugated polymer matrix). The optical spectra of these nanocomposites were compared to the existing models of energy levels in quantum dots. Moreover, by the use of electronic paramagnetic resonance, conclusions about the location and the symmetry of Mn²⁺ ions have been drawn. The nanocomposite energy gap is in the 3.2–3.3 eV range. The size of the nanoparticle is about 3.3 nm and Mn²⁺ ions are located at or near the nanoparticle surface.     

Photoluminescence and field emission properties of ZnS:Mn nanoparticles synthesized by rf-magnetron sputtering technique

Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size 6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm.     

Photoluminescence enhancement of synthesized ZnS-based-nanocrystals and aging effect on its emitting color

Various colors-emitting ZnS:Cu,Cl, ZnS:Cu,Cl,Mn and ZnS:Mn nanocrystals (NCs) which were shown to be about 3 nm sized-particle were synthesized by using a solution chemistry. And the luminescences of the synthesized ZnS-based NCs were investigated through photoluminescence excitation (PLE) and photoluminescence (PL) spectroscopy. The PLE and PL intensities of the ZnS-based NCs depends on their reflux time, and red shifted maximum PLE wavelengths of the synthesized NCs showed with increasing reflux time. The increased maximum PL intensity of NCs with increasing reflux time is due to the enhanced crystallinity of the NCs. And the shifted emitting colors of the NCs showed after aging treatment compared to those of refluxed NCs. The amount of shifted wavelength of Cu,CI doped ZnS, Cu,CI and Mn co-doped ZnS, only Mn doped ZnS NCs were -22 nm, +18 nm, and +14 nm, respectively.     

Solvothermal synthesis of CdS nanorods: role of basic experimental parameters

CdS nanorods with varying dimensions were synthesized by solvothermal process. It was observed that the anions present with the Cd-salts play an important role in determining the dimensions of the CdS nanorods. The crystalline nature of the sources was found to play a crucial role in determining the phase of the products. The nature of the sulfur source, molar ratio of the precursors, filling fraction of the solvent, and the synthesis temperature play important role in defining the size and shape of the products. By controlling the experimental parameters it was possible to control the dimension of the CdS nanorods within a certain range (diameter of the nanorods could be varied within a wide range from approximately 7 to 100 nm by varying the temperature within 100-250 degrees C). Optical absorption, photoluminescence, and Raman studies of these samples were carried out to characterize the CdS nanorods.     

Manganese Doped Fluorescent Paramagnetic Nanocrystals for Dual‐Modal Imaging

In this work, dual‐modal (fluorescence and magnetic resonance) imaging capabilities of water‐soluble, low‐toxicity, monodisperse Mn‐doped ZnSe nanocrystals (NCs) with a size (6.5 nm) below the optimum kidney cutoff limit (10 nm) are reported. Synthesizing Mn‐doped ZnSe NCs with varying Mn²⁺ concentrations, a systematic investigation of the optical properties of these NCs by using photoluminescence (PL) and time resolved fluorescence are demonstrated. The elemental properties of these NCs using X‐ray photoelectron spectroscopy and inductive coupled plasma‐mass spectroscopy confirming Mn²⁺ doping is confined to the core of these NCs are also presented. It is observed that with increasing Mn²⁺ concentration the PL intensity first increases, reaching a maximum at Mn²⁺ concentration of 3.2 at% (achieving a PL quantum yield (QY) of 37%), after which it starts to decrease. Here, this high‐efficiency sample is demonstrated for applications in dual‐modal imaging. These NCs are further made water‐soluble by ligand exchange using 3‐mercaptopropionic acid, preserving their PL QY as high as 18%. At the same time, these NCs exhibit high relaxivity (≈2.95 mM^?1 s^?1) to obtain MR contrast at 25 °C, 3 T. Therefore, the Mn²⁺ doping in these water‐soluble Cd‐free NCs are sufficient to produce contrast for both fluorescence and magnetic resonance imaging techniques.     

Ferromagnetism in Gd-doped CdS dilute magnetic semiconducting nanorods

Cd _x Gd_1?x S (x = 0–0.15) nanorods have been synthesized by solvothermal technique. X-ray diffraction study reveals that pure and Gd-doped CdS nanorods exhibits hexagonal wurtzite structure. Transmission electron microscopy reveals nanorods like morphology of synthesized CdS having 14 and 26 nm size of pure and 15 % doped CdS nanorods. UV–Visible absorption study confirms the blue shift in the energy band energy due to the quantum confinement effects. Photoluminescence spectra confirm the defect free nature of the synthesized nanorods with peaks emerging around 528 and 540 nm due to the green emission. The magnetic study shows that the pure and Gd-doped CdS nanorods exhibits ferromagnetic character and the magnetisation increased by five times from 0.074 to 0.422 emu/g upon Gd-doping.     

Novel approach to control CdS morphology by simple microwave-solvothermal method

Nanosize CdS powders with different microstructures are prepared in different solvents by using rapid microwave irradiation. Effect of solvents and Cd²⁺ precursors are to be able to control the particle size, and microstructures of CdS have been investigated by X-ray diffraction and TEM. The different particle size and morphologies are observed using different Cd²⁺ precursors in different solvents. TEM micrographs clearly show multiarmed nanorods and spherical shape morphologies of CdS powders are obtained in polar solvent like water (H₂O), whereas non-polar polyol solvent like ethylene glycol (EG), prickle and cluster like morphologies of CdS are achieved with different Cd²⁺ precursors such as CdSO₄ and Cd (CH₃COO)₂. The spectroscopy studies of nanosize CdS are examined by photo-luminescence spectra. Band gap and the absorption co-efficient for nano CdS is also evaluated from optical absorption studies.     

Synthesis and optical properties of CdS nanorods and CdSe nanocrystals using oleylamine as both solvent and stabilizer

CdS nanorods and CdSe nanocrystals were prepared via the one-pot synthesis approach in oleylamine (OLA) system. The OLA used in this process as both the solvent and stabilizer is favorable for probing capping mechanism and simplifying experimental steps. The growth process and characterization of cadmium chalcogenide nanocrystals were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM), Ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy. Results demonstrated OLA-capped CdS nanorods and CdSe nanocrystals were highly crystalline and had good optical properties.     

Preparation and optical study of CdS nanocrystals embedded phosphate glass

A new phosphate glass system with CdS nanocrystals dispersed in glass matrix was investigated. The phosphate glass composition with good stability has been used for preparation of CdS doped glasses. The CdS in the range of 0.5-7.0% has been doped into this glass composition. Effect of CdS content on the optical and other properties has been investigated. The optical characterization of the glass samples showed that with increasing concentration of CdS, there was a red shift in transmission cut-off of the glasses. From the transmission cut-off of each glass sample, the band gap of the CdS nanocrystals embedded glass was calculated. The band gap of CdS particles embedded glass was observed in the range of 3.1-4.1 eV. The present system is compared with CdS nanocrystals doped in silica based glass system. In the phosphate glass system, the UV transmission cut-off's are not sharp and the optical transmittance decreases with increasing CdS content in contrast to silica glass system. The reason for such behavior has been discussed in the present investigation. TEM of the CdS doped phosphate glasses showed CdS particle size in the range of 5-7 nm for lower concentration of CdS and 10-100 nm for higher concentration of CdS. The nanocrystals are non-uniform in size but uniformly dispersed in glass matrix.     

Facile synthesis and luminescence characteristics of high-quality CdS: Eu/ZnS core/shell nanocrystals with biocompatibility

In this paper, we report a facile method to synthesize high quality CdS: Eu nanocrystals (NCs) and CdS: Eu/ZnS NCs with strong photoluminescence (PL). The influence of various experimental variables including the concentration of Eu3+ ions, the reaction time and the reaction temperature were investigated systematically. In addition, the PL properties of CdS: Eu NCs exhibited pH sensitive. Under the acid condition, pH value of the CdS: Eu NCs solution played an important role in determining PL emission intensity. However, under the alkaline condition, the obtained CdS: Eu NCs exhibited a tunable PL emission wavelength (from 490 nm to 610 nm) when pH value was adjusted from pH 7 to 10. After coating with ZnS shell, the CdS: Eu/ZnS NCs showed enhanced PL intensity compare with one of the CdS: Eu NCs. The CdS: Eu NCs and CdS: Eu/ZnS NCs were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). In addition, the biocompatibility of these NCs was measured by hemolytic test, which indicated that CdS: Eu/ZnS NCs were more biocompatible than CdS: Eu NCs at the same conditions. It can be expected that CdS: Eu/ZnS NCs are promising biolabeling materials.     

Solvothermal Synthesis of Boehmite and γ-Alumina Nanorods

Boehmite nanorods were synthesized by a solvothermal method using AICl3·6H2O in mixed solvents of water and aniline. The solvothermal time, heating temperature and the concentration of aniline have effects on the morphology of boehmite. γ-alumina nanorods were prepared by a simple thermal transformation of boehmite nanorods. A rational mechanism based on the oriented attachment is proposed for the formation of boehmite nanorods. The products were characterized by X-ray powder diffraction （XRD） and transmission electron microscopy （TEM）. Photoluminescence （PL） spectrum of the boehmite nanorods was also investigated.     

树形分子包覆硫化镉量子点的抗老化性能研究

以聚酰胺-胺树形分子为模板制备了平均粒径为2.5nm的CdS量子点, 采用HRTEM、EDS、UV-vis、PL等手段对样品进行表征, 研究了其在室温避光条件下的老化过程. 结果表明, CdS量子点在刚制备的前5d里UV-vis、PL谱峰半峰宽变窄, 发光效率迅速上升, 表明量子点以尺寸窄化生长为主; 5d后UV-vis、PL谱峰半峰宽逐渐宽化, 发光效率缓慢下降, 表明量子点以尺寸宽化(Ostwald 熟化)过程为主. 树形分子的配位作用和模板作用赋予CdS量子点良好的抗老化性能, 6个月后量子点粒径增量<0.3nm, PL强度约降低22%.     

Photoacoustic spectra on Mn-doped zinc silicate powders by evacuated sealed silica tube method

The non-radiative transition processes on non-doped Zn₂SiO₄ and Zn₂SiO₄:Mn powders with various Mn concentrations were studied by photoacoustic (PA) spectroscopy. Zn₂SiO₄:Mn _x powders were prepared by dry reaction within an evacuated silica glass tube. As the result of photoluminescence (PL) measurement, the increase of PL intensity for green emission on samples doped with Mn between 1% and 6% and the concentration quenching for luminescence on samples doped with Mn between 7% and 12% were confirmed. For the green luminescence on zinc silicate doped with Mn phosphor, the PL decay behavior is assumed to be due to tunneling directly from excited states of electron traps to the excited states of Mn-ion. The Mn content dependence of PL intensity for green emission is well interpreted by tunneling theory and the results of PA spectra, that is, the green emission is assisted by tunneling from non-radiative levels of Mn-ion to luminescencet level as ⁴T₁(⁴G).