Synthesis of Aqueous CdTe Nanocrystals with High Efficient Blue‐Green Emission of Exciton

As one of the most popular nanocrystals (NCs), aqueous CdTe NCs have very weak green emission under conventional synthesis conditions. In this work, we report the first example of blue‐emitting CdTe NCs directly synthesized in aqueous solution by slowing down the growth rate after nucleation. The key for the synthesis is the optimization of NC growth conditions, namely pH range of 7.5 to 8.5, TGA/Cd ratio of 3.6, Cd/Te ratio of 10, and Te concentration of 2×10^?5 mol/L, to get a slow growth rate after nucleation. The as‐prepared blue‐emitting CdTe NCs have small size (as small as 1.9 nm) and bright emission [with 4% photoluminescence quantum yield (PL QY) at 486 nm and 17% PLQY at 500 nm]. Transmission electron microscopy (TEM) images of the as‐prepared CdTe show monodispersed NCs which exhibit cubic zinc blend structure. Moreover, time‐resolved PL decay and X‐ray photoelectron spectroscopy (XPS) results show the as‐prepared NCs have better surface modification by ligand, which makes these luminescent small CdTe NCs have higher photoluminescence quantum yield, compared with NCs synthesized under conventional conditions.     

The preparation of glutathione-capped CdTe quantum dots and their use in imaging of cells

In this paper, different sizes of glutathione-capped CdTe (GSH/CdTe) quantum dots (QDs) have been prepared directly in aqueous solution. The QDs have tunable fluorescence in the range of 510-670 nm, and they also have high photoluminescence quantum yield (PLQY) without any postpreparative treatment. Furthermore, the QDs have strong resistance to photobleaching, and they also have to be considered as cytocompatible. In addition, for the first time, folic acid was covalently conjugated to the GSH/CdTe QDs for imaging of cancer cells, demonstrating their potentially broad application as biolabels.     

Preparation and Optical Properties of CdTe/CdO-nH2O Core/shell Nano-composites in Aqueous Solution

"The deposition of CdO?nH2O on CdTe nanoparticles was studied in an aqueous phase. The CdTe nanocrystals (NCs) were prepared in aqueous solution through the reaction between Cd2+ and NaHTe in the presence of thioglycolic acid as a stabilizer. The molar ratio of the Cd2+ to Te2- in the precursory solution played an important role in the photoluminescence of the ultimate CdTe NCs. The strongest photoluminescence was obtained under 4.0 of Cd2+/Te2- at pH?8.2. With the optimum dosage of Cd(II) hydrous oxide deposited on the CdTe NCs, the photoluminescence was enhanced greatly. The photoluminescence of these nanocomposites was kept constant in the pH range of 8.0-10.0, but dramatically decreased with an obvious blue-shifted peak while the pH was below 8.0. In addition, the photochemical oxidation of CdTe NCs with cadmium hydrous oxide deposition was markedly inhibited."     

Luminescence 3D-ordered porous materials composed of CdSe and CdTe nanocrystals

The luminescence porous materials of CdTe or CdSe nanocrystals (NCs) were prepared by filling the corresponding NCs into the voids of colloidal crystal by co-deposition of polymer beads and NCs. After removing the beads with tetrahydrofuran (THF), the 3D-ordered porous materials of CdTe (or CdSe) NCs were obtained. The wavelength of maximum photoluminescence of the NCs porous material shows obvious red shift compared with their aqueous dispersion. Under the excitation of high-energy electron the porous materials of CdTe and CdSe NCs will emit photons that can be collected to form a cathode luminescence (CL) image.     

Factors governing the quality of aqueous CdTe nanocrystals: calculations and experiment

The aqueous synthesis of thiol-stabilized semiconductor CdTe colloidal nanocrystals has been revisited. We found optimal conditions for the synthesis of high-quality CdTe NCs through a study of the influence of the initial conditions (structure and concentration of Cd-thiol complexes) on the quality of the CdTe nanocrystals. A numerical calculation shows a clear correlation between the concentration of CdL (where L is (SCH(2)COO)(2-)) in the initial solution and the photoluminescence quantum efficiency of the CdTe nanocrystals.     

Microwave-assisted growth and characterization of water-dispersed CdTe/CdS core-shell nanocrystals with high photoluminescence

A novel microwave-assisted method of growth of high-quality CdTe/CdS core-shell nanocrystals in the aqueous phase is presented in this paper. The photoluminescence quantum yield (PLQY) is greatly enhanced by epitaxial growth of the CdS shell. Under optimum conditions, the PLQY of as-prepared nanocrystals reaches as high as 75% without any post-treatment. Furthermore, these investigations demonstrate that microwave irradiation is tremendously useful for fast epitaxial growth of nanocrystals due to its special characteristics. As a result, the microwave synthesis is sufficiently time-economizing (only five minutes are required) to obtain optimum amounts of CdTe/CdS core-shell nanocrystals in comparison to the conventional illumination method (several days are required). Therefore, this current research not only provides a rapid microwave synthesis for producing highly fluorescent CdTe/CdS core-shell nanocrystals, but also it presents some advantages of the microwave synthesis in comparison to the illumination method.     

Systematic study of the photoluminescence dependence of thiol-capped CdTe nanocrystals on the reaction conditions

A modified method to prepare high-quality thiol-capped CdTe nanocrystals (NCs) was reported in this paper. The experimental results showed that the different molar ratios of the ligands (thioglycolic acid) to monomers (Cd2+ ions) in the precursor solution played an important role in the photoluminescence (PL) quantum yield (QY) of the as-prepared CdTe NCs. When [ligand]/[monomer] = 1.2, the maximum fluorescent emission peak appeared in the orange-red window, and the PL QY increased up to 50% at room temperature without any postpreparative treatment. In the meantime, suitable reaction conditions were in favor of the optimization of the surface structure of NCs, resulting in the relatively high PL QY from green to red. In addition, some differences between hydrothermal synthesis and traditional aqueous synthesis of CdTe NCs were discussed.     

一锅合成绿色到近红外发射的CdTe量子点

以3-巯基丙酸(MPA)为稳定剂,采用水相合成法制备了从绿色到近红外发射的CdTe量子点。系统研究了反应液pH值、镉和碲的物质的量之比及镉和3-巯基丙酸的物质的量之比等实验条件对CdTe量子点体系的发射波长和荧光量子产率的影响。在pH值为10.5,且nCd2+∶nTe2-∶nMPA=1∶0.05∶1.1的条件下,回流0.5 h,CdTe量子点体系在569 nm波长处的荧光量子产率达到30.8%;在7 h的回流时间内,制备的量子点的波长覆盖范围为525～730 nm。分别用X射线粉末衍射、透射电镜和红外光谱对CdTe量子点的晶体结构、形貌及表面基团进行表征。     

CdTe纳米晶-BaSO4复合荧光微球的制备

利用表面活性剂双层修饰技术在水溶性荧光CdTe纳米晶表面先后包覆了双十八烷基二甲基溴化铵和十二烷基硫酸钠, 从而在纳米晶外表面引入—SO-4反应位点, 以—SO-4为活性中心进一步制备了包覆CdTe纳米晶的BaSO4复合荧光微球. 通过扫描电子显微镜、透射电子显微镜、共聚焦荧光显微镜和X射线粉末衍射等方法确定了复合微球的尺寸及组成. 由于BaSO4的保护, CdTe-BaSO4复合微球荧光的耐酸性比CdTe原液的提高明显.     

Facile synthesis of nanocrystal encoded fluorescent silica microspheres

Monodisperse CdTe composite microspheres with a spherical shape were prepared using organosilane chemicals in aqueous solution. CdTe nanocrystals (NCs) were loaded into the matrix of silica microspheres during the formation of composite microspheres. Detailed characterization of the CdTe composite microspheres by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spectrofluorimeter was performed to elucidate the morphology and fluorescence of the composite microspheres. In contrast to CdTe NCs in aqueous solution, CdTe NCs in the composite microspheres revealed high stability and fluorescence due to the confined effects of silica matrix. In addition, multicolored CdTe QDs were encoded into the microspheres at precise ratios.     

Chemiluminescence of CdTe nanocrystals induced by direct chemical oxidation and its size-dependent and surfactant-sensitized effect

CdTe nanocrystals (NCs) capped with thioglycolic acid (TGA) were synthesized via a microwave-assisted method. The chemiluminescence (CL) of CdTe NCs induced by directly chemical oxidation and its size-depended and surfactant-sensitized effect in aqueous solution were then investigated. It was found that oxidants, especially hydrogen peroxide and potassium permanganate, could directly oxidize CdTe NCs to produce strong CL emission in basic conditions. The oxidized CL of CdTe NCs displayed size-dependent effect and its intensity increased along with increasing the sizes of the NCs. Moreover, the CL intensity could, if surfactants CTAB or beta-cyclodextrin were added to the above CL system, be sensitized to some degree. The sensitized CL induced by CTAB and beta-cyclodextrin is mainly contributing to the formation of aggregate nanostructure and the micellar micronanoenvironment, respectively. The possible oxidized CL mechanisms were further examined by means of photoluminescence spectra, CL spectra, and transmission electron microscopy studies. The CL properties of CdTe NCs not only will be helpful to study physical chemistry properties of semiconductor nanocrystals but also are expected to find use in many fields such as luminescence devices, bioanalysis, and multicolor labeling probes.     

Synthesis of CdTe nanocrystals through program process of microwave irradiation

A novel method, the program process of microwave irradiation (PPMI), which commendably integrates good qualities of microwave irradiation and a programmed heating process, is presented to synthesize high-quality CdTe nanocrystals in aqueous solution. Microwave irradiation, which acts as the heating mode of PPMI, is highly favorable for a narrow size distribution and low concentration of surface defects of nanocrystals. On the other hand, two correlative processes (the first process and the second process) are utilized in PPMI to actualize the programmed heating process, which is an effective strategy to improve the quality of nanocrystals. Thus, a series (diameters approximately 2-4 nm) of highly luminescent (PLQY approximately 30-68%) CdTe nanocrystals were rapidly prepared (reaction time approximately 1-30 min) in aqueous phase through PPMI.     

Metal‐Enhanced Fluorescence of CdTe Nanocrystals in Aqueous Solution

Metal‐enhanced fluorescence of semiconductor nanocrystals (NCs) is investigated. There is very little attention paid to the metal‐enhanced fluorescence in aqueous solution, which has great potential applications in bioscience. In this work, we directly observe metal‐enhanced fluorescence of CdTe NC solution by simply mixing CdTe NCs and Au nanoparticles, both of which are negatively charged. In order to study this kind of photoluminescence enhancement in aqueous solutions, we propose a calibration method, which takes into account the light attenuation in solutions. After consideration of the light weakening in transmission, the maximal PL enhancement is about 3 times as large as the ones without Au NPs. Some factors related to the enhanced magnitude of fluorescence, for instance, the concentration and the molar feed ratio of CdTe NCs and Au NPs, are studied in detail. Furthermore, the decreased lifetimes of CdTe NCs induced by Au NPs are also obtained, which are in accord with the enhancement of the photoluminescence.     

Easy preparation and characterization of highly fluorescent polymer composite microspheres from aqueous CdTe nanocrystals

Fluorescent microspheres were easily fabricated from aqueous CdTe nanocrystals (NCs). The NCs, which had negative charges on the surface, were first extracted to chloroform by cationic surfactant octadecyl-p-vinyl-benzyldimethylammonium chloride (OVDAC) and then swollen into performed polystyrene (PS) microspheres. Through this method, strong photoluminescence (PL) of aqueous NCs was inherited in the resultant composite microspheres. Moreover, the NCs were firmly stabilized in the microspheres, withstanding not only polar solvents but also nonpolar solvents. UV-vis spectrum, PL spectrum, TEM, and confocal fluorescence microscopy were used to characterize the product.     

Highly Stable CsPbBr3 Nanocrystal Phosphors by Surface Passivation and Encapsulation

The colloidal all-inorganic CsPbX₃(X=I, Br, Cl) perovskite nanocrystals(NCs) with unique optical properties have attracted considerable attention in the field of semiconductor nanocrystals, but their application is hindered by stability issues caused by surface defects and environmental factors. Usually with inert layer encapsulation, the stability of CsPbX₃ NCs can be significantly enhanced. However, due to the loss of highly dynamic oleic acid/oleylamine ligands, it is usually accompanied by a decrease in the photoluminescence quantum yield(PLQY). Herein, we report a facile method for preparing CsPbBr₃ NCs based green phosphors with high stability and bright emission. With modification of colloidal CsPbBr₃ NCs by di-dodecyldimethylammonium bromide and sequent encapsulation in the as-synthesized mesoporous MOF-5, the green emitting phosphors with enhanced stability and a PLQY of 77% were obtained. The phosphors exhibit enhanced resistance against ambient oxygen, UV light, heat treatment and water. These excellent properties show the potential value of our prepared NCs as stable phosphors in light-emitting devices.     

基于聚合物多齿配体的高性能CdTe量子点的微波水相合成

针对当前水相合成的量子点(QDs)光性能与稳定性等方面存在的不足,发展了基于聚合物多齿配体的水相制备策略.利用巯基修饰的聚丙烯酸(PAA-SH)作为多齿配体代替常用的巯基丙酸等单齿配体,结合微波辅助加热制备了CdTe量子点,研究了多齿配体对量子点的生长机制与荧光性能的影响.以PAA-SH为配体制备的CdTe量子点荧光性能优异(荧光量子效率(PLQY)可达75%),流体力学直径较小(~10 nm),稳定性也有明显提高.基于聚合物多齿配体的量子点制备技术有助于实现生物医学研究中急需的兼具高亮度、高稳定性、小尺寸等特征的高性能量子点生物探针的制备.     

Interaction of CdTe nanocrystals with thiol-containing amino acids at different pH: a fluorimetric study

3-Mercaptopropionic acid (MPA)-capped CdTe nanocrystals (NCs) were synthesized in aqueous medium, and their interaction with cysteine (Cys) and homocysteine (Hcy) was studied by steady-state and time-resolved fluorescence spectra at different pH. At 6.4?<?pH?<?8.0, the fluorescence of CdTe NCs can be effectively enhanced by Cys and Hcy. While pH?>?9.6, only Cys quenches the fluorescence of the CdTe NCs, no fluorescence changes are observed for Hcy. Mechanism study shows that these pH manipulating fluorescence responses can be attributed to the following two reasons: first, both the thiol–thiolate equilibrium of Cys (Hcy) and the number of undercoordinated NCs surface sites capped with dual coordinated ligands are strong pH-dependent; second, different thiol-containing amino acids, with different redox energy level, can lead to distinguishable fluorescence responses of NCs. Based on these unique fluorescence responses, the possibilities of developing a sensitive detecting technique for Cys/Hcy and Cys through pH modulation can be explored.     

Special characteristics of fluorescence and resonance Rayleigh scattering for cadmium telluride nanocrystal aqueous solution and its interactions with aminoglycoside antibiotics

CdTe nanocrystals (CdTe NCs) were achieved by reaction of CdCl₂ with KHTe solution and were capped with sodium mercaptoacetate. The product was detected by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), fluorescence spectra, ultraviolet-visible spectra and X-ray diffraction (XRD). The CdTe NCs are of cubic structure and the average size is about 5 nm. The fluorescence quantum yield of CdTe NCs aqueous solution increased from 37% to 97% after 20 d under room light. The maximum λ _em of fluorescence changed from 543 nm to 510 nm and the blue shift was 33 nm. CdTe NCs aqueous solution can be steady for at least 10 months at 4 in° a refrigerator. The resonance Rayleigh scattering (RRS) of CdTe NCs in the aqueous solution was investigated. The maximum scattering peak was located at about 554 nm. The interactions of CdTe NCs with amikacin sulfate (AS) and micronomicin sulfate (MS) were investigated respectively. The effects of AS and MS on fluorescence and RRS of CdTe NCs were analyzed. It was found that AS and MS quenched the photoluminescence of CdTe NCs and enhanced RRS of CdTe NCs. Under optimum conditions, there are linear relationships between quenching intensity (F ₀-F), intensity of RRS (I-I ₀) and concentration of AS and MS. The detection limits (3б) of AS and MS are respectively 3.4 ng·mL⁻¹ and 2.6 ng·mL⁻¹ by the fluorescence quenching method, and 15.2 ng·mL⁻¹ and 14.0 ng·mL⁻¹ by the RRS method. The methods have high sensitivity, thus CdTe NCs may be used as fluorescence probes and RRS probes for the detection of aminoglycoside antibiotics. Supported by the National Natural Science Foundation of China (Grant No. 20475045)     

Electrostatic and covalent interactions in CdTe nanocrystalline assemblies

This paper focuses on the interactions between cysteamine-stabilized CdTe nanocrystals [CdTe(CA) NCs] and thioglycolic-acid-stabilized CdTe nanocrystals [CdTe(TGA) NCs]. These interactions were examined by the absorption, continuous, and time-resolved photoluminescence (PL) spectra of the electrostatically mixed and the covalently linked NCs assemblies comprised of the oppositely surface charged CdTe(CA) and CdTe(TGA) NCs and by a comparison with those of the corresponding pristine NCs. The CdTe(CA)-CdTe(TGA) coupling is dictated by the surfactant spacer, ranging between 0.93 and 1.14 nm and by electrostatic and covalent interactions, enabling a F?rster resonance energy transfer (FRET) process among the NCs. The results revealed an excellent spectral overlap between the emission of the CdTe(TGA) NCs and the absorption of the CdTe(CA) NCs as well as a PL spectral red shift on the formation of electrostatic and covalent interactions. Furthermore, the measurements showed a lifetime ranging between 1.2 and 3 ns for the electrostatically mixed and the covalently linked assemblies, shorter than those of the pristine CdTe(CA) NCs and CdTe(TGA) NCs, both of which measured as approximately 5.5 ns. When CdTe(TGA) NCs performed as the most efficient donors, FRET rates of 10(10)-10(11) s(-1) were calculated for the electrostatically mixed NCs or covalently linked NCs.     

Preparation of monodisperse CdTe nanocrystals-SiO2 microspheres without ligands exchange

Fluorescent CdTe-SiO₂ composite microspheres were prepared by a sol–gel method without the exchange of surface ligands for the first time. We loaded CdTe nanocrystals (NCs) into the matrix of silica microspheres during the formation of composite spheres. In contrast to CdTe NCs in aqueous solutions, CdTe NCs in the composite microspheres revealed better stability while their fluorescence properties were retained due to the confined effects of silica matrix. In addition, we also investigated the dependency of properties of these composite spheres on such important synthesis factors as pH value, concentration and stabilizers during experiment procedure in details.