Quantum Dot Photoluminescence Quenching by Cr(III) Complexes. Photosensitized Reactions and Evidence for a FRET Mechanism

Reported are quantitative studies of the energy transfer from water-soluble CdSe/ZnS and CdSeS/ZnS core/shell quantum dots (QDs) to the Cr(III) complexes trans-Cr(N(4))(X)(2)(+) (N(4) is a tetraazamacrocycle ligand, X(-) is CN(-), Cl(-), or ONO(-)) in aqueous solution. Variation of N(4), of X(-), and of the QD size and composition allows one to probe the relationship between the emission/absorption overlap integral parameter and the efficiency of the quenching of the QD photoluminescence (PL) by the chromium(III) complexes. Steady-state studies of the QD PL in the presence of different concentrations of trans-Cr(N(4))(X)(2)(+) indicate a clear correlation between quenching efficiency and the overlap integral largely consistent with the predicted behavior of a F?rster resonance energy transfer (FRET)-type mechanism. PL lifetimes show analogous correlations, and these results demonstrate that spectral overlap is an important consideration when designing supramolecular systems that incorporate QDs as photosensitizers. In the latter context, we extend earlier studies demonstrating that the water-soluble CdSe/ZnS and CdSeS/ZnS QDs photosensitize nitric oxide release from the trans-Cr(cyclam)(ONO)(2)(+) cation (cyclam = 1,4,8,11-tetraazacyclotetradecane) and report the efficiency (quantum yield) for this process. An improved synthesis of ternary CdSeS core/shell QDs is also described.     

水溶性InP/ZnS量子点的合成及其在指纹显现中的应用

以磷化锌、氯化铟为原料,以十二烷胺为溶剂,在150～200℃下合成了InP量子点,通过相转移和紫外光照得到了巯基乙酸修饰的水溶性InP/ZnS量子点.利用X射线衍射仪、透射电镜、高分辨透射电镜、荧光光谱仪等分析了不同温度下合成的量子点的粒径、形貌、荧光性能及指纹显现效果.结果表明,合成的InP和InP/ZnS量子点为球...     

Highly luminescent InP/GaP/ZnS nanocrystals and their application to white light-emitting diodes

Highly stable and luminescent InP/GaP/ZnS QDs with a maximum quantum yield of 85% were synthesized by in situ method. The GaP shell rendered passivation of the surface and removed the traps. TCSPC data showed an evidence for the GaP shell. InP/GaP/ZnS QDs show better stability than InP/ZnS. We studied the optical properties of white QD-LEDs corresponding to various QD concentrations. Among various concentrations, the white QD-LEDs with 0.5 mL of QDs exhibited a luminous efficiency of 54.71 lm/W, Ra of 80.56, and CCT of 7864 K.     

Effect of CdS Interlayer on Properties of CdTe Based Quantum Dots

Highly luminescent thioglycolic acid-capped CdTe-based core/shell quantum dots (QDs) were synthesized through encapsulating CdTe QDs in various inorganic shells including CdS, ZnS and CdZnS. CdTe/CdS core/shell QDs exhibited a significant redshift of emission peaks (a maximum emission peak of 652 nm for the core/shell QDs and 575 nm for CdTe cores) with increasing shell thickness. In contrast, the redshift of photoluminescence (PL) peak wavelength of CdTe/ZnS QDs was less than 15 nm. The PL peak wavelengths of the core/shell QDs depended strongly on core size and shell thickness. The PL quantum yields (QYs) of the CdTe/CdS core/shell QDs are up to 67 % while that of CdTe/ZnS core/shell QDs is 45 %. A composite CdZnS shell made CdTe cores a high PL QY up to 51 % and broadly adjusted PL spectra (a maximum PL peak wavelength of 664 nm). The epitaxial growth of the shell was confirmed by X-ray powder diffraction analysis and luminescence decay experiments. Because of high PL QYs, tunable PL spectra, and low toxicity from a ZnS surface layer, CdTe/CdZnS core/shell QDs will be great potential for bioapplications.     

Measurement of interfacial toughness of metal film wire and polymer membrane through electricity induced buckling method

Non-toxic, environment-benign colloidal CuInS(2) (CIS) quantum dots (QDs) were synthesized through a facile noninjection, one-pot approach by reacting Cu and In precursors with dodecanethiol dissolved in 1-octadecence at 220 °C. The Cu:In precursor molar ratio was varied from 1:1 to 1:4 to intentionally generate Cu-deficient CIS QDs. Depending on the stoichiometry of the QDs, their emission peak wavelengths were tuned in red-deep red region. More Cu-deficient CIS QDs (Cu:In=1:4) were found to be more efficient than ones with Cu:In=1:1. After successive ZnS shell was overgrown on the surface of core QDs with Cu:In=1:4, the resulting core/shell QDs exhibited a highly efficient yellow emission with a quantum yield of ~50%. A substantially blue-shifted emission from the core/shell QDs versus core ones was described by suggesting an alternative recombination pathway that may be induced by the ZnS shell coating.     

Versatile Tri(pyrazolyl)phosphanes as Phosphorus Precursors for the Synthesis of Highly Emitting InP/ZnS Quantum Dots

Tri(pyrazolyl)phosphanes ( 5 ^R1,R2) are utilized as an alternative, cheap and low‐toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long‐term stable stock solutions (>6 months) of P(OLA)₃ (OLAH=oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)₃ acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530–620 nm and photoluminescence quantum yields (PL QYs) between 51–62 %. A proof‐of‐concept white light‐emitting diode (LED) applying the InP/ZnS QDs as a color‐conversion layer was built to demonstrate their applicability and processibility.     

水热法合成AgInS2/ZnS核/壳结构量子点及其荧光性能

以硫脲为硫源,采用谷胱甘肽(GSH)和柠檬酸钠(SC)为配体,通过水热法制备了水溶性AgInS2/ZnS(AIS/ZnS)核/壳结构量子点。系统研究了反应温度和配体用量对量子点的合成及其荧光性能的影响。采用X射线衍射(XRD)、透射电子显微镜(TEM)、紫外可见吸收光谱(UV-Vis)和光致发光光谱(PL)分别对量子点的物相、形貌和光学性能进行了表征,并考察了量子点的稳定性。实验结果表明,随着反应温度从70℃升高至90℃,促进了ZnS壳层的形成,有效地钝化了量子点的表面缺陷,获得的AIS/ZnS核/壳量子点的发光强度显著提高,发光峰位从600 nm蓝移至580 nm。配体的添加可以有效地平衡Zn^2+的化学反应活性,减缓ZnS壳层的生长,抑制核壳界面缺陷的形成,还能消除量子点的表面态,当nGSH/nZn^2+=2.0,nSC/nZn^2+=2.5时,AIS/ZnS量子点的荧光性能最佳。此外,AIS/ZnS核/壳结构量子点还具有优异的光学稳定性。     

油溶性CuInS2/ZnS量子点的制备及其温敏性聚丙烯酰胺胶束介导的水相转移

采用非热注法成功制备了高质量的油溶性CuInS2/ZnS核壳量子点,量子点的荧光发射峰在可见光到近红外范围内可调(550～800 nm),且荧光量子产率最高达80%。本文进一步利用具有温敏特性的聚丙烯酰胺胶束作相转移剂,成功地将油溶性的CuInS2/ZnS核壳量子点转移入水相。水相中自组装形成的CuInS2/ZnS量子点-胶束复合物不仅具有良好的荧光性质,而且胶束原有的灵敏的热响应性被保留。这些研究初步表明,无镉的低毒的CuInS2/ZnS量子点可作为纳米胶束的荧光示踪探针。     

Luminescence of Polyethylene Glycol Coated CdSeTe/ZnS and InP/ZnS Nanoparticles in the Presence of Copper Cations

The use of click chemistry for quantum dot (QD) functionalization could be very promising for the development of bioconjugates dedicated to in vivo applications. Alkyne–azide ligation usually requires copper(I) catalysis. The luminescence response of CdSeTe/ZnS nanoparticles coated with polyethylene glycol (PEG) is studied in the presence of copper cations, and compared to that of InP/ZnS QDs coated with mercaptoundecanoic acid (MUA). The quenching mechanisms appear different. Luminescence quenching occurs without any wavelength shift in the absorption and emission spectra for the CdSeTe/ZnS/PEG nanocrystals. In this case, the presence of copper in the ZnS shell is evidenced by energy‐filtered transmission electron microscopy (EF‐TEM). By contrast, in the case of InP/ZnS/MUA nanocrystals, a redshift of the excitation and emission spectra, accompanied by an increase in absorbance and a decrease in photoluminescence, is observed. For CdSeTe/ZnS/PEG nanocrystals, PL quenching is enhanced for QDs with 1) smaller inorganic‐core diameter, 2) thinner PEG shell, and 3) hydroxyl terminal groups. Whereas copper‐induced PL quenching can be interesting for the design of sensitive cation sensors, copper‐free click reactions should be used for the efficient functionalization of nanocrystals dedicated to bioapplications, in order to achieve highly luminescent QD bioconjugates.     

油溶性CuInS2/ZnS量子点的制备及其温敏性聚丙烯酰胺胶束介导的水相转移

采用非热注法成功制备了高质量的油溶性CuInS₂/ZnS核壳量子点, 量子点的荧光发射峰在可见光到近红外范围内可调(550~800 nm), 且荧光量子产率最高达80%。本文进一步利用具有温敏特性的聚丙烯酰胺胶束作相转移剂, 成功地将油溶性的CuInS₂/ZnS核壳量子点转移入水相。水相中自组装形成的CuInS₂/ZnS量子点-胶束复合物不仅具有良好的荧光性质, 而且胶束原有的灵敏的热响应性被保留。这些研究初步表明, 无镉的低毒的CuInS₂/ZnS量子点可作为纳米胶束的荧光示踪探针。     

CdSe/ZnS量子点敏化太阳能电池电子注入与光伏性能表征

合成了CdSe/ZnS核壳结构量子点(QDs), 将其作为光敏剂吸附在TiO2纳米晶薄膜上, 组装成量子点敏化太阳能电池(QDSSCs), 从电子注入速率和电池性能两方面对QDSSCs进行了表征. 为了定量研究ZnS层包覆对电子注入的影响, 运用飞秒瞬态光谱技术, 测试了包覆ZnS前后, CdSe-TiO₂体系的电子注入速率. 实验测得ZnS包覆前后电子注入速率分别为7.14×10¹¹s^-1和2.38×10^-11s^-1, 可以看出包覆后电子注入速率明显降低, 仅为包覆前的1/3. 电池器件J-V性能测试表明, ZnS作为绝缘层包覆在CdSe的表面有效提高了QDSSCs的填充因子和稳定性, 但同时也导致了效率的降低. 上述结果说明了电子注入速率的降低是导致电池电流和效率下降的重要原因, 为今后优化核壳结构QDSSCs的电流和效率提供了依据.     

发光可调Au:ZnCdS合金量子点的水相合成

以巯基丙酸作为配体,在水溶液中合成了发光位置在495~583 nm可调的Au∶Zn Cd S合金量子点,研究了掺杂含量、Zn/Cd比和p H等对量子点光学性质的影响。对预提纯的Au∶Zn Cd S核量子点进行Zn S包覆,量子点表面的缺陷被有效去除,发光效率明显提高。利用X-射线粉末衍射、透射电子显微镜对其结构和形貌进行了表征。     

Room temperature fabrication of hollow ZnS and ZnO architectures by a sacrificial template route

Hollow ZnS and ZnO architectures are fabricated by employing Zn(5)(CO(3))(2)(OH)(6) microspheres as the sacrificial template. Zn(5)(CO(3))(2)(OH)(6) microspheres can be effectively converted into the core/shell structured ZnO/ZnS composites (in the Na(2)S solution) and hollow ZnO architectures (in the KOH solution), by a spontaneous ion replacement reaction at room temperature. Removing the core by the KOH treatment of core/shell structured ZnO/ZnS, hollow ZnS spheres with different shell thicknesses can be effectively achieved. The obtained hollow ZnO architectures exhibit unique geometrical shapes, and their walls are composed of nanocrystals, which are connected to each other to form their hemispherical or circular shape. A possible formation process from Zn(5)(CO(3))(2)(OH)(6) microspheres to core/shell structured ZnO/ZnS composites is proposed by arresting a series of intermediate morphologies.     

硫脲修饰ZnSe:Cu量子点的水相合成及荧光特性

以3-巯基丙酸为稳定剂在水相中合成了Cu掺杂的ZnSe量子点(QDs), 并利用硫脲(CH₄N₂S)对其进行表面修饰, 制备出核壳结构的ZnSe:Cu/ZnS 量子点. 制得的量子点呈闪锌矿结构, 尺寸约为5 nm, 有较好的分散性, 其荧光发射峰在460 nm左右. 经CH₄N₂S修饰后, 量子点表面形成了宽禁带的ZnS包覆层, 将电子和空穴限域在了ZnSe:Cu 核内, 减少了表面发生非辐射复合的载流子, 显著提高了量子点的荧光强度. 与Na₂S、硫代乙酰胺(TAA)等常用硫源相比, 以CH₄N₂S为硫源制得的ZnSe:Cu/ZnS 量子点壳层厚度可控, 表面钝化效果更好, 显示出更佳的荧光效率和稳定性. ZnSe:Cu/ZnS 量子点经过紫外线照射后消除了表面的悬空键, 进一步提高了其量子产率, 最终获到了具有较好荧光性质的ZnSe:Cu/ZnS量子点.     

溶剂热合成的Cu掺杂ZnCdS量子点的发光性质研究

以低毒、廉价的环己烷为溶剂,通过调控杂质离子和基质材料阳离子的相对反应活性,合成了发光颜色可调、近似球形的Cu∶Zn Cd S量子点。系统研究了油胺的用量、Cu掺杂量、Cd/Zn比以及不同的Zn前驱体对量子点发光性质的影响。通过在Cu∶Zn Cd S量子点晶核外层包覆宽带隙Zn S材料,进一步消除了粒子的表面缺陷,有效提高了量子点的发光效率。     

水溶性的CdSe/CdS/ZnS量子点的合成及表征

用L-半胱氨酸盐(Cys)作为稳定剂,合成了水溶性的双壳结构的CdSe/CdS/ZnS半导体量子点。吸收光谱和荧光光谱结果表明,双壳结构的CdSe/CdS/ZnS纳米微粒比单一的CdSe核纳米粒子和单核壳结构的CdSe/CdS纳米粒子具有更优异的发光特性。用透射电子显微镜(TEM)、ED、XRD、XPS和FTIR等方法对CdSe核和双壳层的CdSe/CdS/ZnS纳米微粒的结构、分散性及形貌分别进行了表征。     

Reverse micelle-derived Cu-doped Zn1−xCdxS quantum dots and their core/shell structure

Reverse micelle chemistry-derived Cu-doped Zn_1?xCd_xS quantum dots (QDs) with the composition (x) of 0, 0.5, 1 are reported. The Cu emission was found to be dependent on the host composition of QDs. While a dim green/orange emission was observed from ZnS:Cu QDs, a relatively strong red emission could be obtained from CdS:Cu and Zn_0.5Cd_0.5S:Cu QDs. Luminescent properties of undoped QDs versus Cu-doped ones and quantum yields of alloyed ZnCdS versus CdS QDs are compared and discussed. To enhance Cu-related red emission of CdS:Cu and Zn_0.5Cd_0.5S:Cu core QDs, core/shell structured QDs with a wider band gap of ZnS shell are also demonstrated.     

One-pot synthesis of highly luminescent InP/ZnS nanocrystals without precursor injection

InP/ZnS core/shell nanocrystals are prepared using a single-step heating-up method relying on the difference in reactivity of the applied InP and ZnS precursors. The obtained particles exhibit size-dependent emission in the range of 480-590 nm, a fluorescence quantum yield of 50-70%, and high photostability.     

Gallium Sulfide Quantum Dots with Zinc Sulfide and Alumina Shells Showing Efficient Deep Blue Emission

Solution-processed quantum dot (QD) based blue emitters are of paramount importance in the field of optoelectronics. Despite large research efforts, examples of efficient deep blue/near UV-emitting QDs remain rare due to lack of luminescent wide band gap materials and high defect densities in the existing ones. Here, we introduce a novel type of QDs based on heavy metal free gallium sulfide (Ga₂S₃) and their core/shell heterostructures Ga₂S₃/ZnS as well as Ga₂S₃/ZnS/Al₂O₃. The photoluminescence (PL) properties of core Ga₂S₃ QDs exhibit various decay pathways due to intrinsic defects, resulting in a broad overall PL spectrum. We show that the overgrowth of the Ga₂S₃ core QDs with a ZnS shell results in the suppression of the intrinsic defect-mediated states leading to efficient deep-blue emission at 400 nm. Passivation of the core/shell structure with amorphous alumina yields a further enhancement of the PL quantum yield approaching 50 % and leads to an excellent optical and colloidal stability. Finally, we develop a strategy for the aqueous phase transfer of the obtained QDs retaining 80 % of the initial fluorescence intensity.     

Controlling charge separation and recombination rates in CdSe/ZnS type I core-shell quantum dots by shell thicknesses

Type I core/shell quantum dots (QDs) have been shown to improve the stability and conversion efficiency of QD-sensitized solar cells compared to core only QDs. To understand how the shell thickness affects the solar cell performance, its effects on interfacial charge separation and recombination kinetics are investigated. These kinetics are measured in CdSe/ZnS type I core/shell QDs adsorbed with anthroquinone molecules (as electron acceptor) by time-resolved transient absorption spectroscopy. We show that the charge separation and recombination rates decrease exponentially with the shell thickness (d), k(d) = k(0)e(-βd), with exponential decay factors β of 0.35 ± 0.03 per ? and 0.91 ± 0.14 per ?, respectively. Model calculations show that these trends can be attributed to the exponential decrease of the 1S electron and hole densities at the QD surface with the shell thickness. The much steeper decrease in charge recombination rate results from a larger hole effective mass (than electron) in the ZnS shell. This finding suggests possible ways of optimizing the charge separation yield and lifetime by controlling the thickness and nature of the shell materials.