CdSe/ZnSe/ZnS多壳层结构量子点的制备与表征

展示了一种简捷的多壳层量子点合成路线。在含有过量Se源的CdSe体系中直接注入Zn源,"一步法"合成了CdSe/ZnSe量子点;进一步以CdSe/ZnSe为"核",表面外延生长ZnS壳层制备了核/壳/壳结构CdSe/ZnSe/ZnS量子点。相对于以往报道的多壳层结构量子点的制备方法,该方法通过减少壳层的生长步骤有效地简化了实验操作,缩短了实验周期,同时减少对原料的损耗。对量子点进行高温退火处理,能够大幅提高CdSe/ZnSe/ZnS量子点的发光量子产率。透射电镜、XRD以及光谱研究表明:所制备的量子点接近球形,核与壳层纳米晶均为闪锌矿结构,最终获得的CdSe/ZnSe/ZnS量子点的光致发光量子产率达到53％。为了实现量子点的表面生物功能化,通过巯基酸进行了表面配体交换修饰,使量子点表面具有水溶性的羧基功能团,并且能够维持较高的光致发光量子产率。     

ZnO/ZnS核-壳量子点的双光子吸收效应

利用飞秒激光Z-扫描与泵浦-探测技术,研究了室温下ZnO/ZnS与ZnO/ZnS/Ag核-壳胶体量子点的双光子吸收效应.研究发现:ZnO基核-壳量子点的本征双光子吸收系数比ZnO体材料增大了3个数量级;测量得到的660 nm处的ZnO/ZnS核-壳量子点双光子吸收截面约为4.3×10^-44 cm⁴·s·photon^-1,比相应的ZnS、ZnSe及 CdS量子点大2个数量级;当ZnO/ZnS核-壳量子点镶嵌了银纳米点时,非线性吸收有所增强.ZnO基复合纳米结构的双光子吸收增强可归因于量子限域与局域场效应.     

Development and Investigation of Ultrastable PbS/CdS/ZnS Quantum Dots for Near‐Infrared Tumor Imaging

Achieving bright, reliable, robust, and stable probes for in vivo imaging is becoming extremely urgent for the cancer imaging research community. To date very few works have reported on elucidating in the varied and chemically complex biological milieu. The authors report detailed investigations of the synthesis of near‐infrared, water dispersive, strongly luminescent, and highly stable PbS/CdS/ZnS core/shell/shell quantum dots (QDs). These QDs are extremely stable, they could keep their initial morphology, dispersion status, and photoluminescence (PL) in phosphate buffered saline buffer for as long as 14 months. The QDs also show excellent photostability and could keep ≈80% of their initial PL intensity after 1 h continuous, strong UV illumination. More interestingly, they show negligible toxicity to cultured cells even at high QDs concentration. Given these outstanding properties, the QDs are explored for in vivo, tumor imaging in mice. With one order of magnitude lower QD concentration (0.04 mg mL^–1), significantly weaker laser intensity (0.04 W cm^–2 vs ≈1 W cm^–2), and considerably shorter signal integration time (≤1 ms vs hundreds of ms) as compared to the best reported rare earth doped nanoparticles, the QDs show high emission intensity even at injection depth of ≈2.5 mm.     

Efficient Quantum Dot Light-Emitting Diodes Based on Well-Type Thick-Shell CdxZn1−xS/CdSe/CdyZn1−yS Quantum Dots

Device grade quantum dots (QDs) require QDs ensembles to retain their original superior optical properties as in solution. QDs with thick shells are proven effective in suppressing the inter-dot interaction and preserving the emission properties for QDs solids. However, lattice strain–induced defects may form as the shell grows thicker, resulting in a notable photoluminescence quenching. Herein, a well-type Cd_xZn_1−xS/CdSe/Cd_yZn_1−yS QDs is proposed, where ternary alloys CdZnS are adopted to match the lattice parameter of intermediate CdSe by separately adjusting the x and y parameters. The resultant thick-shell Cd_0.5Zn_0.5S/CdSe/Cd_0.73Zn_0.27S QDs reveal nonblinking properties with a high PL QY of 99% in solution and 87% in film. The optimized quantum dot light-emitting diodes (QLEDs) exhibit a luminance of 31547.5 cd m⁻² at the external quantum efficiency maximum of 21.2% under a bias of 4.0 V. The shell thickness shows great impact on the degradation of the devices. The T₅₀ lifetime of the QLEDs with 11.2 nm QDs reaches 251 493 h, which is much higher than that of 6.5 and 8.4 nm QDs counterparts. The performances of the well-type thick-shell QLEDs are comparable to state-of-the-art devices, suggesting that this type of QDs is a promising candidate for efficient optoelectronic devices.     

Shell thickness dependence of exciton trapping in colloidal core/shell nanorods

We quantitatively investigated, by time-resolved photoluminescence (PL) spectroscopy, the shell thickness dependence of exciton trapping and its effects on the PL quantum yield (QY) in colloidal CdSe/CdS/ZnS core/shell quantum rods. The defects passivation, due to a thin shell (0.6 monolayer), leads to a 2 times reduction of the trapping from both emitting and high-energy excited states, thus explaining the observed 4.3 times increase of the PL QY. Moreover, the QY decrease in the thick shell (1.3 monolayers) sample is fully explained in terms of increased trapping from the emitting states, which is ascribed to new defects caused by the strain relaxation at the core-shell interface.     

HgTe/CdS/ZnS多壳层量子点的制备与表征

采用一种简单的方法合成HgTe/CdS/ZnS多壳层量子点。首先,以1-硫代甘油为稳定剂,在水相溶液中制备出HgTe核量子点;然后,采用外延生长法依次在HgTe核量子点表面包覆CdS和ZnS壳层,合成出最终具有稳定近红外发光的HgTe/CdS/ZnS多壳层量子点。该合成方法仅需3个步骤,具有操作简单、成本低廉的优点。实验结果显示,当反应温度为90 ℃、反应溶液pH为11.0、反应加热回流时间为4 min时,HgTe/CdS/ZnS多壳层量子点具有最高荧光量子产率36%。     

Investigation of Novel Quantum Dots/Proteins/Cellulose Bioconjugate Using NSOM and Fluorescence

We investigated the engineered bioconjugate of cadmium selenide core/zinc sulfide shell, (CdSe)ZnS, quantum dots (QDs) with genetically modified proteins using fluorescence spectroscopy, near-field scanning optical microscopy (NSOM) and spectroscopy (NSOS). The protein polymer was allowed to self-assemble to the bacterial microcrystalline cellulose surface through the cellulosic binding domain. Results from the sample containing the QDs/protein/cellulose assemblies suggest that QDs were arrayed along the cellulose surface. The spectroscopic change of spectroscopic properties of the QDs upon bioconjugation, indicating the interaction among the immobilized QDs and between the constructed protein and QDs.     

Linear dipole behavior of single quantum dots encased in metal oxide semiconductor nanoparticles films

Understanding of charge/energy exchange processes and interfacial interactions that occur between quantum dots (QDs) and the metal oxides is of critical importance to these QD-based optoelectronic devices. This work reports on linear dipole behavior of single near-infrared emitting CdSeTe/ZnS core/shell QDs which are encased in indium tin oxide (ITO) semiconductor nanoparticles films. A strong polarization anisotropy in photoluminescence emission is observed by defocused wide-field imaging and polarization measurement techniques, and the average polarization degree is up to 0.45. A possible mechanism for the observation is presented in which the electrons, locating at single QD surface from ITO by electron transfer due to the equilibration of the Fermi levels, result in a significant Stark distortion of the QD electron/hole wavefunctions. The Stark distortion results in the linear polarization property of the single QDs. The investigation of linear dipole behavior for single QDs encased in ITO films would be helpful for further improving QD-based device performance.     

Facile synthesis of mercaptosuccinic acid-capped CdTe/CdS/ZnS core/double shell quantum dots with improved cell viability on different cancer cells and normal cells

Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdS_thin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ～3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications.     

基于CuInS2/ZnS核壳结构量子点的高光效暖白光LED

采用逐步热注射法合成了用于白光LED的CuInS₂/ZnS(CIS/ZnS)核壳结构量子点.通过调整Cu/In的比率, 在CuInS₂(CIS)量子点的基础上, 合成了发射波长在570~650 nm之间可调的CIS/ZnS量子点.与CIS量子点的低量子产率相比, 具有核壳结构的CIS/ZnS量子点的量子产率达到了78%.通过在黄光荧光粉YAG :Ce³⁺表面旋涂CIS/ZnS量子点的方式制备了暖白光LED器件.在工作电流为10 mA时, 暖白光LED的发光效率达到了244.58 lm/W.由于CIS/ZnS量子点的加入, 所制备的白光LED器件的显色指数达到86.7且发光颜色向暖色调发生了转移, 相应的色坐标为(0.340 6, 0.369 0).     

Copper- or manganese-doped ZnS quantum dots as fluorescent probes for detecting folic acid in aqueous media

3-Mercaptopropionic acid-capped core/shell ZnS:Cu/ZnS and ZnS:Mn/ZnS doped quantum dots (QDs) prepared through hydrothermal methods exhibit high photoluminescence intensity as well as good photostability. These water-dispersible nanoparticles exhibit high fluorescence sensitivity to folic acid due to the high affinity of the carboxylate groups and nitrogen atoms of folic acid towards the Zn surface atoms of the doped dots. Quenching of the fluorescence intensity of the QDs allows the detection of folic acid concentrations as low as 11 μM, thus affording a very sensitive system for the sensing of this biologically active molecule in aqueous solution. The possible quenching mechanism is discussed.     

Temperature-dependent photoluminescence of CuInS2 quantum dots

Temperature-dependent photoluminescence (PL) spectroscopy of CuInS₂ core and CuInS₂/ZnS core–shell quantum dots (QDs) was studied for understanding the influence of a ZnS shell on the PL mechanism. The PL quantum yield and lifetime of CuInS₂ core QDs were significantly enhanced after the QD surface was coated with the ZnS shell. The temperature dependences of the PL energy, linewidth, and intensity for the core and core–shell QDs were studied in the temperature range from 92 to 287 K. The temperature-dependent shifts of 98 meV and 35 meV for the PL energies of the QDs were much larger than those of the excitons in their bulk semiconductors. It was surprisingly found that the core and core–shell QDs exhibited a similar temperature dependence of the PL intensity. The PL in the CuInS₂/ZnS core–shell QDs was suggested to originate from recombination of many kinds of defect-related emission centers in the interior of the cores.     

Cell labeling and cytotoxicity of aqueously synthesized CdTe/CdS/ZnS core–shell–shell quantum dots by a water bath-hydrothermal method

CdTe/CdS/ZnS core–shell–shell quantum dots (QDs) were synthesized in aqueous solution via water-bathing combined hydrothermal method using L-cysteine as a stabilizer. The present method features markedly reduced synthesis time, higher fluorescent intensity and lower cytotoxicity of the QDs. Structural and spectroscopic properties of core–shell–shell QDs are well characterized by absorption and fluorescence spectroscopy, X-ray diffraction, transmission electron microscopy, and fourier transform infrared spectroscopy. Both CdS and ZnS shells were capped on the CdTe core and the fluorescence was greatly enhanced by the ZnS coating. The ternary QDs conjugated with transferrins were successfully employed for the biolabeling and fluorescent imaging of HeLa cells. Cytotoxicity evaluation shows that CdTe/CdS/ZnS was less toxic for cells than CdTe and CdTe/CdS due to the presence of a ZnS coating on surface, which inhibited the release of cadmium ions.     

Physical reasons of emission transformation in infrared CdSeTe/ZnS quantum dots at bioconjugation

The core/shell CdSeTe/ZnS quantum dots (QDs) with emission at 780–800 nm (1.55–1.60 eV) have been studied by means of photoluminescence (PL) and Raman scattering methods in the nonconjugated state and after conjugation to different antibodies (Ab): (i) mouse monoclonal [8C9] human papilloma virus Ab, anti-HPV 16-E7 Ab, (ii) mouse monoclonal [C1P5] human papilloma virus HPV16 E6+HPV18 E6 Ab, and (iii) pseudo rabies virus (PRV) Ab. The transformations of PL and Raman scattering spectra of QDs, stimulated by conjugated antibodies, have been revealed and discussed.The energy band diagram of core/shell CdSeTe/ZnS QDs has been designed that helps to analyze the PL spectra and their transformations at the bioconjugation. It is shown that the core in CdSeTe/ZnS QDs is complex and including the type II quantum well. The last fact permits to explain the nature of infrared (IR) optical transitions (1.55–1.60 eV) and the high energy PL band (1.88–1.94 eV) in the nonconjugated and bioconjugated QDs. A set of physical reasons has been analyzed with the aim to explain the transformation of PL spectra in bioconjugated QDs. Finally it is shown that two factors are responsible for the PL spectrum transformation at bioconjugation to charged antibodies: (i) the change of energy band profile in QDs and (ii) the shift of QD energy levels in the strong quantum confinement case. The effect of PL spectrum transformation is useful for the study of QD bioconjugation to specific antibodies and can be a powerful technique for early medical diagnostics.     

Synthesis of NIR‐Emitting InAs‐Based Core/Shell Quantum Dots with the Use of Tripyrazolylarsane as Arsenic Precursor

Tris(3,5‐dimethylpyrazolyl)arsane (1) is introduced as a low‐cost and convenient to handle arsenic precursor for the straight forward synthesis of InAs quantum dots (QDs). Transamination of 1 with the solvent oleylamine (OLAH) gives trioleylarsane (As(OLA)₃) which in the presence of the reducing agents diisobutylaluminum hydride (DIBAL‐H) or trioleylphosphane (P(OLA)₃) yields InAs QDs via a typical hot injection approach. The size of the obtained InAs core QDs are tuned by varying the reaction time, the amount of the applied reducing agent, or even more effectively by changing the indium and/or zinc halide precursors, InX₃, and ZnX₂ (Cl, Br, or I). Passivation of the resulting InAs particles with a protective ZnS or ZnSe shell results in improved photoluminescence of the core/shell QDs covering a spectral range between 600 and 1150 nm.     

Mn掺杂ZnSe量子点变温发光性质研究

量子点(QD)照明器件中电流导致的焦耳热会使其工作温度高于室温,因此研究量子点的发光热稳定性十分重要。本文利用稳态光谱和时间分辨光谱研究了具有不同壳层厚度的Mn掺杂ZnSe(Mn: ZnSe)量子点的变温发光性质,温度范围是80～500 K。实验结果表明,厚壳层(6.5单层(MLs))Mn: ZnSe量子点的发光热稳定性要优于薄壳层(2.6 MLs)的量子点。从80 K升温到400 K的过程中,厚壳层Mn: ZnSe量子点的发光几乎没有发生热猝灭,发光量子效率在400 K高温下依然可以达到60%。通过对比Mn: ZnSe量子点的变温发光强度与荧光寿命,对Mn: ZnSe量子点发光热猝灭机制进行了讨论。最后,为了研究Mn: ZnSe量子点的发光热猝灭是否为本征猝灭,对具有不同壳层厚度的Mn: ZnSe量子点进行了加热-冷却循环(300-500-300 K)测试,发现厚壳层的Mn: ZnSe量子点的发光在循环中基本可逆。因此,Mn: ZnSe量子点可以适用于照明器件,即使器件中会出现不可避免的较强热效应。     

界面电子转移对量子点荧光闪烁行为的影响

利用激光扫描共聚焦显微系统分别测量了CdSe/ZnS量子点在SiO2玻片表面、铟锡氧化物(ITO)纳米粒子表面和聚甲基丙烯酸甲酯(PMMA)薄膜表面上的荧光闪烁行为.研究发现,不同界面环境中量子点的亮态发光持续时间的概率密度都服从指数修正的幂律分布P(t)∝t-αexp(-t/μ).与处于SiO2玻片表面的情况相比,在ITO表面上的单量子点具有非常短暂的亮态发光持续时间,而在PMMA表面的单量子点亮态发光持续时间最长.这种荧光闪烁行为的不同主要归因于量子点与三种材料之间的界面电子转移特性.     

Energy transfer dynamics between Alq3 and CdTeS/ZnS core shell nanocrystals

The photoluminescence (PL) properties of the guest-host films, using CdTeS/ZnS core shell quantum dots (QDs) as the guest and organic small-molecule material Alq₃ as the host, are studied by steady-state and time-resolved PL spectroscopy. Both the relative intensity and the PL lifetime are intensively dependent on the weight ratio of Alq₃ and CdTeS/ZnS QDs. The detailed analysis provides clear evidence for a Förster energy transfer from Alq₃ host to QDs guest, based on the nonradiative resonant transfer mechanism. The results are relevant to the application of hybrid organic/inorganic systems to OLEDs.     

Analysis of room temperature PL spectra of InAs/GaAs/InP and InAs/InP self-assembled QDs: A five-band study

In this paper, room temperature PL spectra of InAs self-assembled dots grown on GaAs/InP and InP substrate are presented. For analyzing different positions of the PL peaks, we examine the strain tensor in these quantum dots (QDs) using a valence force field model, and use a five-band k·p formalism to find the electronic spectra. We find that the GaAs tensile-stained layer affects the position of room temperature PL peak. The redshift of PL peak of InAs/GaAs/InP QDs compared to that of InAs/InP QDs is explained theoretically.     

Impurity absorption in ZnSe/InP/ZnS core/shell/shell spherical quantum dots

Impurity states in ZnSe/InP/ZnS core/shell/shell spherical quantum dot where electrons are localized in the InP shell are considered using variational method. It is assumed that the hydrogenlike impurity is located in the center of quantum dot core (ZnSe). The impurity ground state wave function and energy, as well as electron binding energy are obtained. Interband direct transitions from the ground valence state into the ground donor state are considered. Dependences of absorption edge on the inner and outer radii of the quantum layer are derived.