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1.
N. De La Rosa-Fox A. Santos M. Piñero L. Esquivias L. Gago-Duport E. Hoinkis 《Journal of Sol-Gel Science and Technology》1998,13(1-3):629-633
Size and size distribution of the semiconductor nanocrystals embedded in a dielectric matrix play a dominant role in line broadening and the exciton quantum confinement level. The results show new aspects of the CdS and CdSe crystal growth as quantum dots using small angle neutron scattering techniques (SANS). Thus, the crystal growth influences the aggregation process of the silica network. The intensity difference of the scattering between the silica matrix and the composite accounts for the crystal size and their volume fraction. Under similar conditions CdS nanocrystals grow faster and bigger than CdSe ones. 相似文献
2.
Huang F Chen G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,70(2):318-323
The water-soluble L-cysteine-modified CdSe/CdS core/shell nanocrystals (expressed as CdSe/CdS/Cys nanocrystals) have been synthesized in aqueous by using L-cysteine as stabilizer. The size, shape, component and spectral property of CdSe/CdS/Cys nanocrystals were characterized by high-resolution transmission electron microscope (HRTEM), energy dispersive X-ray fluorescence (EDX), infrared spectrum (IR) and photoluminescence (PL). The results showed that the spherical CdSe/CdS/Cys nanocrystals with an average diameter of 2.3 nm have favorable fluorescent property, theirs photostability and fluorescence intensity are enhanced greatly after overcoating with CdS. The cysteine modified on the surface of core/shell CdSe/CdS nanocrystals renders the nanocrystals water-soluble and biocompatible. Based on the fluorescence quenching of the nanocrystals in the presence of calf thymus deoxyribonucleic acid (ct-DNA), a fluorescence quenching method has been developed for the determination of ct-DNA by using the nanocrystals as a novel fluorescence probe. The pH value of the system was selected at pH 7.4, with excitation and emission wavelength at 380 and 522 nm, respectively. Under the optimal conditions, the fluorescence quenching intensity of the system is linear with the concentration of ct-DNA in the range of 0.1-3.5 microg/mL (r=0.9987). The detection limit is 0.06 microg/mL. And two synthetic samples were analyzed satisfactorily. 相似文献
3.
Large-scale synthesis of nearly monodisperse CdSe/CdS core/shell nanocrystals using air-stable reagents via successive ion layer adsorption and reaction 总被引:10,自引:0,他引:10
Li JJ Wang YA Guo W Keay JC Mishima TD Johnson MB Peng X 《Journal of the American Chemical Society》2003,125(41):12567-12575
Successive ion layer adsorption and reaction (SILAR) originally developed for the deposition of thin films on solid substrates from solution baths is introduced as a technique for the growth of high-quality core/shell nanocrystals of compound semiconductors. The growth of the shell was designed to grow one monolayer at a time by alternating injections of air-stable and inexpensive cationic and anionic precursors into the reaction mixture with core nanocrystals. The principles of SILAR were demonstrated by the CdSe/CdS core/shell model system using its shell-thickness-dependent optical spectra as the probes with CdO and elemental S as the precursors. For this reaction system, a relatively high temperature, about 220-240 degrees C, was found to be essential for SILAR to fully occur. The synthesis can be readily performed on a multigram scale. The size distribution of the core/shell nanocrystals was maintained even after five monolayers of CdS shell (equivalent to about 10 times volume increase for a 3.5 nm CdSe nanocrystal) were grown onto the core nanocrystals. The epitaxial growth of the core/shell structures was verified by optical spectroscopy, TEM, XRD, and XPS. The photoluminescence quantum yield (PL QY) of the as-prepared CdSe/CdS core/shell nanocrystals ranged from 20% to 40%, and the PL full-width at half-maximum (fwhm) was maintained between 23 and 26 nm, even for those nanocrystals for which the UV-vis and PL peaks red-shifted by about 50 nm from that of the core nanocrystals. Several types of brightening phenomena were observed, some of which can further boost the PL QY of the core/shell nanocrystals. The CdSe/CdS core/shell nanocrystals were found to be superior in comparison to the highly luminescent CdSe plain core nanocrystals. The SILAR technique reported here can also be used for the growth of complex colloidal semiconductor nanostructures, such as quantum shells and colloidal quantum wells. 相似文献
4.
5.
We reported a facile route for overcoating CdS and ZnS shells around colloidal CdSe core nanocrystals. To synthesize such
double shelled core/shell nanocrystals, first, CdSe core nanocrystals were prepared in a much “greener” and cheap route, which
did not involve the use of hazardous and expensive trioctylphosphine. Then, a low-cost and labor-saving route was adopted
for the CdS and ZnS shell growth with the use of thermal decomposition of commercial available air stable single-source precursors
cadmium diethyldithio-carbamate and zinc diethyldithiocarbamate in a non-coordinating solvent at intermediate temperatures.
Powder X-ray diffraction patterns and transmission electron microscopy images confirm the epitaxial growth of the shell in
the core/shell nanocrystals. The photoluminescence quantum yield of the resulting CdSe/CdS/ZnS core/shell nanocrystals can
be as high as 90% in organic media and up to 60% after phase transfer into aqueous media. By varying the size of CdSe cores,
the emission wavelength of the obtained core/shell nanostructures can span from 554 to 636 nm. 相似文献
6.
Liu Y Kim M Wang Y Wang YA Peng X 《Langmuir : the ACS journal of surfaces and colloids》2006,22(14):6341-6345
A dendron ligand with two carboxylate anchoring groups at its focal point and eight hydroxyl groups as its terminal groups was found to efficiently convert as-synthesized CdSe/CdS core-shell nanocrystals in toluene to water-soluble dendron-ligand stabilized nanocrystals (dendron nanocrystals). The resulting dendron nanocrystals retained 60% of the photoluminescence value of the original CdSe/CdS core-shell nanocrystals in toluene and were significantly brighter than the similar dendron nanocrystals with thiolate (deprotonated thiol group) as the anchoring group which retained just 10% of the photoluminescence value of the original CdSe/CdS core-shell nanocrystals in toluene. The carboxylate-based dendron nanocrystals survived UV irradiation in air for at least 13 days, about 9 times better than the thiolate-based dendron nanocrystals (35 h) and similar to that of the thiolate-based dendron-box stabilized CdSe/CdS core-shell nanocrystals (box nanocrystals). Upon UV irradiation, the dendron nanocrystals became even 2 times brighter than the original CdSe/CdS core-shell nanocrystals in toluene, and the UV-brightened PL can retain the brightness for at least several months. These stable and bright dendron nanocrystals were soluble in various aqueous media, including all common biological buffer solutions tested, for at least 1.5 years. In addition to their superior performance, the synthetic chemistry of carboxylate dendron ligands and the corresponding dendron nanocrystals is relatively simple and with high yield. 相似文献
7.
YUE Yang GE Mei-ying LIU Yan WU Jie CHEN Ping LIN Lie LIU Yu-feng SUN Yan CHEN Xin DAI Ning 《高等学校化学研究》2010,26(6):871-875
We described a facile method for preparing CdSe/CdS/ZnS core/shell/shell nanocrystals from air-stable single source precursors.The single source precursors of cadmium ethylxanthate and zinc ethylxanthate were used to form CdS and ZnS shell layers in octadecene.An efficient modification of CdSe/CdS/ZnS nanocrystals was subsequently performed to obtain hydrophilic nanocrystal fluorophores with good stability in a pH range of 1.6-10. 相似文献
8.
Reaction of 3-aminopropylsilyl-modified ZnO microrods with trioctylphosphineoxide-coated CdSe/CdS core/shell nanocrystals in THF produces rod-shaped nanoparticle clusters that show directional photoemission that can be tuned with the size of the CdSe nanocrystals. The observed waveguiding effect of these microstructures is due to total internal reflection of light at the cluster-air interface. 相似文献
9.
Semiconductor nanocrystals are of a great interest for many practical applications which motivates the search of low cost and environmental-friendly methods for their manufacturing. Here we report the synthesis of CdSe and CdS nanoparticles utilizing composite matrix of liquid paraffin as a non-coordinating solvent and stearic acid as a coordinating ligand. The nanoparticle growth kinetics is compared to that of the classical synthesis in trioctylphosphine oxide matrix. It is found that the nucleation and crystal growth are remarkably affected by the coordinating ligand. The CdSe and CdS nanocrystals can be isolated and purified from the matrix which makes it possible their large-scale synthesis for applications. 相似文献
10.
We show that the length of the alkyl chain of surface ligands can shift the equilibrium between the wurtzite and zinc blende polytypes of CdSe nanocrystals. In-situ wide-angle X-ray scattering measurements reveal that short-chain (e.g., propyl) phosphonic acids stabilize CdSe nanocrystals with the zinc blende phase whereas octadecylphosphonic acid stabilize nanocrystals with the wurtzite phase. We also demonstrate how this effect can be used to improve the shape selectivity in the synthesis of anisotropic CdSe/CdS and ZnSe/CdS nanoheterostructures. 相似文献
11.
介观结构SiO2/CdO纳米复合物为前驱体原位水热合成半导体CdSe和CdS纳米晶 总被引:2,自引:0,他引:2
以高度有序的介观结构SiO2/CdO纳米复合物为前驱体,在硒源或硫源存在的还原性条件下,利用原位水热反应,合成了介观结构SiO2/CdSe及SiO2/CdS纳米复合物,除去SiO2后,得到半导体CdSe及CdS纳米晶.通过X射线衍射(XRD),高分辨率透射电镜(HRTEM),X射线能散射谱(EDX)及选区电子衍射(SAED)等手段对产物进行了组成和结构表征.结果表明,介观结构SiO2主体材料在合成过程中起到了一定的形貌和尺寸限制作用,得到的CdSe和CdS均为直径在8 nm左右的类球形六方相纳米晶. 相似文献
12.
13.
We report a new green synthetic route of CdSe and core-shell CdSe/CdS nanoparticles (NPs) in aqueous solutions. This route is performed under water-bath temperature, using Se powder as a selenium source to prepare CdSe NPs, and H(2)S generated by the reaction of Na(2)SH(2)SO(4) as a sulfur source to synthesize core-shell CdSe/CdS NPs at 25-35 degrees C. The synthesis time of every step is only 20 min. After illumination with ambient natural light, photoluminescence (PL) intensities of CdSe NPs enhanced up to 100 times. The core-shell CdSe/CdS NPs have stronger photoactive luminescence with quantum yields over 20%. The obtained CdSe NPs exhibit a favorable narrow PL band (FWHM: 50-37 nm) with increasing molar ratio of Cd/Se from 4:1 to 10:1 at pH 9.1 in the crude solution, whereas PL band of corresponding CdSe/CdS NPs is slightly narrower. The emission maxima of nanocrystals can be tuned in a wider range from 492 to 592 nm in water by changing synthesis temperature of CdSe core than those reported previously. The resulting new route is of particular interest as it uses readily-available reagents and simple equipment to synthesize high-quality water-soluble CdSe and CdSe/CdS nanocrystals. 相似文献
14.
Inorganic cluster syntheses of TM2+-doped quantum dots (CdSe, CdS, CdSe/CdS): physical property dependence on dopant locale 总被引:1,自引:0,他引:1
A series of colloidal transition-metal-doped chalcogenide semiconductor nanocrystals (TM2+:CdSe, TM2+:CdS, etc.) has been prepared by thermal decomposition of inorganic cluster precursors. It is shown through extensive spectroscopic and structural characterization that the nanocrystals prepared following literature procedures for synthesis of TM2+:CdSe nanocrystals actually possess an unintended CdSe/TM2+:CdS core/shell morphology. The conditions required for successful formation of TM2+:CdSe and TM2+:CdS by cluster decomposition have been determined. Magneto-optical and photoluminescence spectroscopic results for this series of doped nanocrystals reveal major physical consequences of dopant localization within the shell and demonstrate the capacity to engineer dopant-carrier exchange interactions via core/shell doping strategies. The results presented here illustrate some of the remarkable and unexpected complexities that can arise in nanocrystal doping chemistries and emphasize the need for meticulous characterization to avoid false positives. 相似文献
15.
This paper describes synthesis and optical properties of planar clusters of CdSe nanocrystals. The clusters emit linearly polarized light in the plane of the cluster. The emission wavelength of the clusters can be adjusted between 568 and 639 nm with the size of the CdSe nanocrystals. Planar CdSe microclusters were synthesized by reaction of trioctylphosphine oxide-coated CdSe/CdS nanocrystals with 3-aminopropylsilyl-modified Ca(2)Nb(3)O(10) nanosheets in THF. The clusters are 3.92 +/- 1.18 mum length/width and 91 +/- 37 nm thickness, and they consist of alternating layers of Ca(2)Nb(3)O(10) to which CdSe nanocrystals are attached with densities of 5300 +/-310 particles per side of a single Ca(2)Nb(3)O(10) sheet. The chemical inertness of the clusters in coordinating solvents suggests covalent interactions between the aminopropyl groups and CdSe nanocrystals. Upon excitation at lambda(exc) = 400 nm, the clusters emit green (568 nm), orange (589 nm), or red (639 nm) light, depending on the size of the CdSe crystals. The light is emitted preferentially in the cluster plane and it is linearly polarized along the cluster edges. Combined fluorescence microscopy and atomic force microscopy reveal that the directional emission efficiency depends linearly on the thickness of the clusters, which varies between 70 and 180 nm. The ability to manipulate the direction and polarization of the photoemission of CdSe nanoparticles via assembly into 2D structures is of interest for applications of these and similar structures in advanced optical materials and devices. 相似文献
16.
D.A. Hummel I.L. Torriani A.F. Craievich N. Fox de la Rosa A.Y. Ramos O. Lyon 《Journal of Sol-Gel Science and Technology》1997,8(1-3):285-291
Small-angle X-ray scattering (SAXS) experiments were carried out to characterize the structure of the composite formed by
CdSe nanocrystals embedded in a popous silica matrix (silica xerogels containing Cd with formamide addition and ultrasound
treatment). SAXS results from samples before Se diffusion indicate the presence of heterogeneities with a bimodal size distribution
which was associated to the existence of mesopores (pores of several hundred Å) immersed in a nanoporous matrix (characteristic
pore radii of 20–30 Å). The diffusion of Se induces the nucleation and growth of CdSe nanocrystals. The average size of the
nanocrystals increases with Cd content. Higher Se doses promote the formation of larger nanocrystals (radius of gyration of
∼30 to 50 Å). Anomalous scattering results confirm the existence of Se aggregation associated with CdSe nanocrystal formation
and suggest that only partial segregation of Cd and Se occurs. 相似文献
17.
本文报道在Sol-gel基材中制备由聚合物稳定的CdS纳米晶的新方法, 即通过甲基丙烯酸镉与甲基丙烯酸羟乙酯共聚合合成了含有Cd 2+的聚合物微凝胶, 在聚合物微凝胶网络中原位聚合正硅酸乙酯形成聚合物互穿的Sol-gel复合基材. 再向该聚合物/二氧化硅复合基材中通入H2S气体得到CdS纳米晶. 在聚合物网络中原位聚合正硅酸乙酯可以降低纯二氧化硅材料的脆性; 另一方面, 二氧化硅可以作为增强剂增加聚合物材料的强度. 因此, 在我们合成的聚合物/二氧化硅复合基材中制备的CdS纳米晶将具有很好的应用前景. 相似文献
18.
Bingquan Jia Dr. Du Sun Dr. Wei Zhao Prof. Fangfang Xu Prof. Fuqiang Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(35):7955-7960
Semiconductor nanocrystals of tunable shell/core configurations have great potential in photo-driven applications such as photoluminescence and photocatalysis, but few strategies realize a controllable synthesis with respect to both the size of the core and the shell with high crystallinity. Here, a new synthetic method based on cadmium cyanamide (CdNCN) nanoparticle anion exchange reactions was developed to access solid or hollow CdSe nanocrystals with tunable size and CdNCN@CdS heterostructures with modulated shell/core thickness. The gradual shift and narrow width of photoluminescence features demonstrate the high crystallinity and monodispersity of the resulting CdSe nanocrystals. In the CdNCN@CdS heterostructures, synergistic effects of the photocarrier separation is observed between the CdS shell and CdNCN core, which leads to great improvement in photocatalysis with optimized shell/core ratio. 相似文献
19.
Luminescent CdSe/CdS core/shell nanocrystals in dendron boxes: superior chemical,photochemical and thermal stability 总被引:5,自引:0,他引:5
The surface ligands, generation-3 (G3) dendrons, on each semiconductor nanocrystal were globally cross-linked through ring-closing metathesis (RCM). The global cross-linking of the dendron ligands sealed each nanocrystal in a dendron box, which yielded box-nanocrystals. Although the dendron ligands coated CdSe nanocrystals (CdSe dendron-nanocrystals) were already quite stable, the stability of CdSe box-nanocrystals against chemical, photochemical, and thermal treatments were dramatically improved in comparison to that of the original dendron-nanocrystals. Furthermore, the box structure of the ligands monolayer coupled with the stable inorganic CdSe/CdS core/shell nanocrystals resulted in a class of extremely stable nanocrystal/ligands complexes. The band edge photoluminescence of the core/shell dendron-nanocrystals and box-nanocrystals were partially remained, and could be further brightened through controlled chemical oxidation or photooxidation. Practically, the stability of the box-nanocrystals is sufficient for most fundamental studies and technical applications. The box-nanocrystals may represent a general solution for the commonly encountered instability for many types of colloidal nanocrystals. The size distribution of the empty dendron boxes formed by the dissolution of the inorganic nanocrystals in concentrated HCl was very narrow. The empty boxes as new types of polymer capsules are soluble in solution, mesoporous, and with a very thin but stable peripheral. Those nanometer-sized cavities should be of interest for many purposes in the field of solution host-guest chemistry. 相似文献
20.
FEI Xiao-fang SHAN Gui-ye KONG Xiang-gui WANG Xin ZENG Qing-hui ZHANG You-lin 《高等学校化学研究》2005,21(6):728-733
IntroductionSemiconductor nanocrystals show strong size-de-pendent properties when their size is similar to or smal-ler than the excition Bohr radius of the bulk materialsand quantum confinement occurs for the space-con-fined motion of the electrons and holes in the nano-re-gion of materials[1—5].Because of the excellent opticaland electronic properties,semiconductor nanocrystalsare currently being investigated as emitting materials forthin-film light-emitting devices(LED)[6,7],low-thresh-ol… 相似文献