Ultrafast Carrier Dynamics in CdSe/CdS/ZnS Quantum Dots

The intra- and inter-band relaxation dynamics of CdSe/CdS/ZnS core/shell/shell quantum dots are investigated with the aid of time-resolved nonlinear transmission spectra which are obtained using femtosecond pump-probe technique. By selectively exciting the core and shell carrier, the dynamics are studied in detail. Carrier relaxation is found faster in the conduction band of the CdS shell （about 130 fs） than that in the conduction band of the CdSe core （about 400 fs）. From the experiments it is distinctly demonstrated the existence of the defect states in the interface between the CdSe core and the CdS shell, indicating that ultrafast spectroscopy might be a suitable tool in studying interface and surface morphology properties in nanosystems.

Effect of gamma irradiation on optical properties of CdSe/ZnS quantum dots embedded in PDMS

The optical properties of CdSe/ZnS quantum dots(QDs)embedded in polydimethylsiloxane(PDMS)flexible materials after irradiated withγ-rays were studied.As an embedding matrix,PDMS exhibits the advantage of high radiation hardness.The luminescence spectra and fluorescence lifetime of the irradiated and unirradiated samples were tested.The fluorescence intensity of QDs decreases with the increase of the irradiation dose according to the result of luminescence spectra.The fluorescence intensity of the QDs decreases by 80%after irradiation with a dose of 1 kGy,but the position of the emission peak and the spectral shape of the QDs remain consistent before and after irradiation.In addition,the fluorescence lifetime of QDs is shortened after irradiation.Based on the fluorescence response of QDs to the irradiation ofγ-rays and combined with flexible materials,our work provides a theoretical basis for the application of QDs as a new wearable dosimeter.

Water-soluble CdSe/ZnS quantum dots passivated by poly(glycino amino acid) phosphazenes

Poly(organophosphazenes) have potential applications in making water-soluble and biocompatible quantum dots (QDs) due to their wide variety of properties. The CdSe QDs of green emission and the core-shell CdSe/ZnS QDs of red emission were prepared. Subsequently the trioctylphosphine oxide-stabilized CdSe/ZnS QDs were transferred from chloroform into water through a ligand exchange process with poly(glycino amino acid)phosphazenes, which can be obtained from the saponification of poly (glycino amino ester)phosphazenes at room temperature. The resulting QDs-polymer nanocomposite particles can form colloidally stable suspensions in water and exhibit good photostability.

Exciton radiative lifetime in CdSe quantum dots

Colloidal CdSe quantum dots(QDs)are promising materials for solar cells because of their simple preparation pro-cess and compatibility with flexible substrates.The QD radiative recombination lifetime has attracted enormous attention as it affects the probability of photogenerated charges leaving the QDs and being collected at the battery electrodes.However,the scaling law for the exciton radiative lifetime in CdSe QDs is still a puzzle.This article presents a novel explanation that recon-ciles this controversy.Our calculations agree with the experimental measurements of all three divergent trends in a broadened energy window.Further,we proved that the exciton radiative lifetime is a consequence of the thermal average of decays for all thermally accessible exciton states.Each of the contradictory size-dependent patterns reflects this trend in a specific size range.As the optical band gap increases,the radiative lifetime decreases in larger QDs,increases in smaller QDs,and is weakly depend-ent on size in the intermediate energy region.This study addresses the inconsistencies in the scaling law of the exciton life-time and gives a unified interpretation over a widened framework.Moreover,it provides valuable guidance for carrier separa-tion in the thin film solar cell of CdSe QDs.

氢氟酸处理InP/GaP/ZnS量子点的光学性能及其发光二极管应用

采用氢氟酸(HF)原位注入法制备了InP/GaP/ZnS量子点。通过紫外/可见/近红外光谱、光致发光光谱、透射电镜、球差校正透射电镜、X射线衍射、X射线光电子能谱等测试手段分析了HF对InP量子点的发光性能影响。实验结果表明,HF刻蚀减少了量子点表面氧化缺陷状态,有效控制了InP核表面的氧化,并且原子配体形式的F-钝化了量子点表面的悬挂键,显著提升了量子点的光学性能。HF处理的InP/GaP/ZnS量子点具有最佳的发光性能,PLQY高达96%。此外,用HF处理InP/GaP/ZnS量子点制备的发光二极管,其发光的电流效率为6.63 cd/A,最佳外量子效率(EQE)为3.83%。

Synthesis and characterization of ZnS-based quantum dots to trace low concentration of ammonia

In the present work,a solution-based co-precipitation method has been adopted to synthesize pure and cobalt-doped ZnS quantum dots and characterized by XRD,SEM,TEM with EDX,FTIR and gas sensing properties.XRD analysis has shown a single phase of ZnS quantum dots having a zinc blend structure.TEM and XRD line broadening indicated that the average crystallite size in the sample is in the range of 2 to 5 nm.SEM micrographs show spherical-shaped quantum dots.FTIR studies show that cobalt has been successfully doped into the ZnS cubic lattice.EDX spectra have analyzed the elemental presence in the samples and it is evident that the spectra confirmed the presence of cobalt(Co),zinc(Zn),oxygen(O),and sulphur(S)elements only and no other impurities are observed.The ZnS-based quantum dot sensors reveal high sensitivity towards 50 ppm of ammonia vapors at an operating temperature of 70℃.Hence,ZnS-based quantum dots can be a promising and quick traceable sensor towards ammonia sensing applications with good response and recovery time.

Large-scale control of enhancement and quenching of photoluminescence for ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution

We investigated the optical properties of hybrid exciton–plasmon coupling ensembles composed of ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution. We modulated their average interval by changing the ratio of quantum dots and Ag nanoparticles. The transition from dramatic PL enhancement to PL quenching state was experimentally observed, according to the continuous decrease of the PL lifetime. The PL enhancement rate exceeded 10, with the Purcell factor of 3.5. Meanwhile, the proportion of fast decay increased from 0.3 to 0.6, corresponding to the proportion of slow decay decreased from 0.7 to 0.4. Our experiment is important for the hybrid exciton–plasmon coupling system to be practicable in optoelectronic application.

Temperature dependence of the photoluminescence of MnS/ZnS core–shell quantum dots

The temperature dependence of the photoluminescence（PL） from Mn S/Zn S core–shell quantum dots is investigated in a temperature range of 8 K–300 K. The orange emission from the ^4T1→^6A1transition of Mn^2＋ions and the blue emission related to the trapped surface state are observed in the Mn S/Zn S core–shell quantum dots. As the temperature increases, the orange emission is shifted toward a shorter wavelength while the blue emission is shifted towards the longer wavelength. Both the orange and blue emissions reduce their intensities with the increase of temperature but the blue emission is quenched faster. The temperature-dependent luminescence intensities of the two emissions are well explained by the thermal quenching theory.

In-situ Synthesis of SnO2 Quantum Dots/ZnS Nanosheets Heterojunction as a Visible-light-driven Photocatalyst for Degradation of Rhodamine B,Potassium Dichromate and Tetracycline

The SnO2 quantum dots(SnO2QDs)/ZnS nanosheets(ZnSNs)heterojunction was fabricated via an in-situ synthetic method at room temperature.Rhodamine B,potassium dichromate,and tetracycline were used to discuss the photocatalytic activities of the as-prepared samples under the visible light illumination.The photocatalytic mechanism of the as-prepared samples was also proposed.The experimental results indicate that the degradation efficiency of the as-prepared SnO2QDs/ZnSNs heterojunction first increases and then decreases with increasing the usage of ZnSNs.When the mass ratio of SnO2QDs to ZnSNs is 1:2 in 180 min,the as-prepared samples have the highest degradation efficiency of 89.1%for rhodamine B,97.7%for potassium dichromate,and 83.8%for tetracycline,which are much higher than 51.7%,26.8%,and 0.9%of pure SnO2QDs as well as 37.9%,87.1%,and 19.1%of pure ZnSNs,respectively.After it is repeatedly degraded for 3 times,it possesses the degradation efficiency of 62.5%for rhodamine B,which increases by 200.5%in comparison with 20.8%of the pure SnO2QDs.Moreover,the enhanced photocatalytic performances of the as-prepared hybrids are attributed to the formation of heterojunction between the SnO2QDs and ZnSNs.In addition,hydroxyl radicals and superoxide anion radicals play major roles during the photocatalytic degradation process,while holes play a minor role.

Synthesis of CdSe quantum dots

Water-soluble CdSe quantum dots(QDs) were synthesized in aqueous solution with thioglycollic acid as stabilizer.CdSe QDswere characterized using Transmission electron microscopy(TEM),UV-Vis absorption spectrum(UV-Vis) and fluorescence spectra(FL).The characterization results indicate that as-synthesized CdSe QD was uniform at about 3.5 nm.

碳量子点-CdSe@ZnS纳米晶双荧光二氧化硅纳米粒子的制备

采用N-(β-氨乙基-γ-氨丙基)甲基二甲氧基硅烷修饰的碳量子点与正硅酸四乙酯共水解的方式制备了碳量子点-CdSe@ZnS纳米晶双荧光二氧化硅纳米粒子(CdSe@ZnS//CDs-mSiO_(2))。通过考察CdSe@ZnS//CDs-mSiO_(2)的微观形貌及荧光特征,证明了碳量子点和CdSe@ZnS纳米晶被成功地包覆在了多孔SiO_(2)纳米粒子的内部,并且具有明显的双荧光特性。通过调整碳量子点和CdSe@ZnS纳米晶的比例以及CdSe@ZnS纳米晶的发射波长可获得丰富的荧光变化,显示出其在荧光编码和防伪以及生物标记领域的应用潜力。

Citrate-stabilized CdSe/CdS quantum dots as fluorescence probe for protein determination

A rapid, ultrasensitive and convenient fluorescence measurement technology based on the enhancement of the fluorescence intensity resulting from the interaction of functionalized CdSe/CdS quantum dots （QDs） with bov/ne serum albumin （BSA） was proposed. The citrate-stabilized CdSe/CdS （QDs） were synthesized by using Se powder and Na2S as precursors instead of any pyrophoric organometallic precursors. The modified CdSe/CdS QDs are brighter and more stable against photobleaching in comparison with organic fluorophores. At pH 7.0, the fluorescence signal of CdSe/CdS is enhanced by increasing the concentration of BSA in the range of 0.1-10 μg/mL, and the low detection limit is 0.06 μg/mL. A linear relationship between the enhanced fluorescence peak intensity （△F） and BSA concentration （c） is established using equation △F=50.7c＋16.4 （R=0.996 36）. Results of determination for BSA in three synthetic samples are identical with the true values, and the recovery （98.9%-102.4%） and relative standard deviation （RSD, 1.8%-2.5%） are satisfactory.

Photocatalytic degradation of Brilliant Green dye using CdSe quantum dots hybridized with graphene oxide under sunlight irradiation

CdSe quantum dots(QDs)hybridized with graphene oxide(GO)are synthesized by a facile chemical precipitation method.The absorption of the CdSe/GO nanocomposite is increased with a significantblue shift with respect to CdSe QDs.The specific surface area of the CdSe/GO nanocomposite is10.4m2/g,which is higher than that of CdSe QDs(5m2/g).The PL intensity of the CdSe/GO nanocomposite is lower than that of the CdSe QDs owing to the inhibition of the recombination of electron‐hole pairs in the composite.In Raman analysis,the two bands of the CdSe/GO nanocomposite are shifted to higher wavenumbers with respect to graphene oxide,which is attributed to electron injection that is induced by CdSe QDs into graphene oxide.Using the Brilliant Green dye,the photocatalytic reduction efficiency of CdSe QDs and the CdSe/GO nanocomposite under sunlight irradiation for90min are approximately81.9%and95.5%,respectively.The calculated photodegradation rate constants for CdSe QDs and the CdSe/GO nanocomposite are0.0190min–1and0.0345min–1,respectively.The enhanced photocatalytic activity of the CdSe/GO nanocomposite can be attributed to the high specific surface area and the reduction of electron‐hole pair recombination because of the introduction of graphene oxide.

Synthesis of CdSe quantum dots via paraffin liquid and oleic acid

This paper reported an efficient and rapid method to produce highly monodispersed CdSe quantum dots (QDs), in which the traditional trioctylphosphine oxide (TOPO) was replaced by paraffin liquid as solvent and oleic acid as the reacting media. The experimental conditions and the properties of QDs had been studied in detail. The resulting samples were confirmed of uniform size distribution with transmission electronic microscopy (TEM), while UV-vis absorption and photoluminescence (PL) spectra clearly indicated that such synthesized QDs had good fluorescence properties.

Graphene quantum dots assisted photovoltage and efficiency enhancement in CdSe quantum dot sensitized solar cells

CdSe quantum dot sensitized solar cells （QDSCs） modified with graphene quantum dots （GQDs） have been successfully achieved in this work for the first time. Satisfactorily, the optimized photovoltage （Voc） of the modified QDSCs was approximately 0.04 V higher than that of plain CdSe QDSCs, consequently improving the photovoltaic performance of the resulting QDSCs. Served as a novel coating on the CdSe QD sensitized photoanode, GQDs played a vital role in improving Voc due to the suppressed charge recombination which has been confirmed by electron impedance spectroscopy as well as transient photovoltage decay measure- ments. Moreover, different adsorption sequences, concentration and deposition time of GQDs have also been systematically investigated to boost the power conversion efficiency （PCE） of CdSe QDSCs. After the coating of CdSe with GQDs, the resulting champion CdSe QDSCs exhibited an improved PCE of 6.59% under AM 1.5G full one sun illumination.

Study on the Interaction between CdSe Quantum Dots and Bovine Serum Albumin with Ultraviolet Visible Absorption Spectroscopy

The interaction of CdSe quantum dots （QDs） with bovine serum albumin （BSA） has been investigated with ultraviolet visible absorption spectroscopy （UVAS）. It was found that the absorption intensity of CdSe QDs significantly decreased after adding BSA solution, showing that CdSe QDs were bonded to BSA. The binding molar ratio was 1：1 and the binding constant was 9.7 × 10^6 L mol^-1.

Selective Synthesis and Advanced Characteristic of CdSe Semiconductor Quantum Dots by Aqueous Phase

This work mainly investigated the influences of some factors, such as, synthesis methods, precursor alteraatives, and vacuum heat-treating process, etc, on the fluorescent characteristics of the semiconductor quantum dots synthesized by aqueous phase. The research results indicate that the fluorescent characteristic of water- solution sample prepared from Na2 SO3 precursor was sensitive to water bath heating time, and specially, its photohuninescence spectrum shows the unique phenomenon of double excitation and emission peaks. Meanwhile, the fluorescent characteristic of water- solution sample prepared from NaBH4 precursor is slightly influenced by water bath heating time, and the sugface of CdSe quantum dots could be passivated by the excessive amount of NaBH4 precursor, which results in the effective decrease of surface traps and great enhancement of quantum yield. Furthermore, the fluorescent emission peaks of samples could be sharpened by vacuum heat-treating process, with its spectral full width at half of maximum （FWHM） around 30- 40 run, so the emission peaks become redshifi, of which the intensity greatly increases.

Direct Synthesis of Zn_(1-x)Cd_xS (0≤x≤1) Quantum Dots in Aqueous Solution and Application in Biology

A simple procedure was presented to directly synthesize Zn1_xCdxS （0 ≤x≤1） quantum dots （QDs） in aqueous solution. QDs＇ structures and properties were characterized by TEM （transmission electron microscopy）, XRD （X-ray diffraction） and fluorescence microscopy. For those as-synthesized Zn1_xCdxS QDs, when the molar ratio between Zn and Cd changed from 1 to 0, its photoluminescence （PL） emission peak shifted from 430 nm to 675 nm. PL emission quantum efficiency was up to 15%. The experiment results demonstrated that those alloyed QDs showed a good biocompatibility and could be used as labelling materials in cell biology.

Room-Temperature Organic Negative Differential Resistance Device Using CdSe Quantum Dots as the ITO Modification Layer

Room-temperature negative differential resistance （NDR） has been observed in different types of organic materials. However, detailed study on the influence of the organic material on NDR performance is still scarce. In this work, room-temperature NDR ＆ observed when CdSe quantum dot （QD） modified ITO is used as the electrode. Furthermore, material dependence of the NDR performance is observed by selecting materials with different charge transporting properties as the active layer, respectively. A peak-to-valley current ratio up to 9 is observed. It is demonstrated that the injection barrier between ITO and the organic active layer plays a decisive role for the device NDR performance. The influence of the aggregation state of CdSe QDs on the NDR performance is also studied, which indicates that the NDR is caused by the resonant tunneling process in the ITO/CdSe QD/organic active layer structure.

Stability and luminescence properties of CsPbBr_(3)/CdSe/Al core-shell quantum dots

To improve the stability and luminescence properties of CsPbBr_(3)QDs,we proposed a new core-shell structure for CsPbBr_(3)/CdSe/Al quantum dots(QDs).By using a simple method of ion layer adsorption and a reaction method,CdSe and A1 were respectively packaged on the surface of CsPbBr_(3)QDs to form the core-shell CsPbBr_(3)/CdSe/Al QDs.After one week in a natural environment,the photoluminescence quantum yields of CsPbBr_(3)/CdSe/Al QDs were greater than 80%,and the PL intensity remained at 71%of the original intensity.Furthermore,the CsPbBr_(3)/CdSe/Al QDs were used as green emitters for white light-emitting diodes(LEDs),with the LEDs spectrum covering 129%of the national television system committee(NTSC)standard color gamut.The core-shell structure of QDs can effectively improve the stability of CsPbBr_(3)QDs,which has promising prospects in optoelectronic devices.