Chemiluminescence resonance energy transfer in the luminol-CdTe quantum dots conjugates

The luminol-CdTe quantum dots (QDs) conjugates were prepared through the reaction between -NH₂ and -COOH. The resonance energy transfer between chemiluminescence donor (luminol-H₂O₂ system) and quantum dots (QDs, with different emission peaks) acceptors (CRET) was investigated. The luminescence of QDs in luminol-QDs conjugates in the process of CRET was influenced by the molar ratio of luminol/QDs. It could reach higher luminescence intensity while the luminol/QDs value was 1/1. Quantum yield of QDs and overlapping areas between the emission spectrum of luminol and adsorption spectrum of QDs played important roles in the CRET efficiency of luminol-QDs conjugates. The higher CRET efficiency (21.2%) was observed when the 540 nm QDs were used as acceptors. This work will offer helpful knowledge for the CRET studies based on QDs.     

CdTe量子点与罗丹明B水溶液体系下的双光子激发荧光共振能量转移

采用时间分辨荧光光谱技术研究了在双光子激发下不同尺寸的量子点与罗丹明B 之间的荧光共振能量转移. 研究结果表明, 在800 nm的双光子激发条件下, 体系间能量转移效率随着供体吸收光谱与受体荧光光谱的光谱重叠程度增加而增加; 理论分析表明, 供体和受体间的Förster半径增加是导致其双光子能量转移效率增大的物理原因. 同时, 研究了罗丹明B浓度对荧光共振能量转移效率的影响. 研究结果表明, 量子点的荧光寿命随着罗丹明B浓度的增加而减小; 量子点与罗丹明B之间的荧光共振能量转移效率随着罗丹明B浓度的增加而增加; 当罗丹明B浓度为3.0×10^-5 mol·L^-1时, 双光子荧光共振能量转移效率为40.1%.     

Experimental investigation of energy transfer between CdSe/ZnS quantum dots and different-sized gold nanoparticles

Hybrid nanostructures of quantum dots(QDs) and metallic nanostructure are attractive for future use in a variety of optoelectronic devices. For photodetection applications, it is important that the photoluminescence (PL) of QDs is quenched by the metallic nanostructures. Here, the quenching efficiency of CdSe/ZnS core-shell quantum dots (QDs) with different sized gold nanoparticles (NPs) films through energy transfer is investigated by measuring the PL intensity of the hybrid nanostructures. In our research, the gold NPs films are formed by the post-annealing of the deposited Au films on the quartz substrate. We find that the energy transfer from the QDs to the Au NPs strongly depends on the sizes of the Au NPs. For CdSe/ZnS QDs direct contact with the Au NPs films, the largest energy transfer efficiency are detected when the resonance absorption peak of the Au NPs is nearest to the emission peak of the CdSe/ZnS QDs. However, when there is a PMMA spacer between the QDs layer and the Au NPs films, firstly, we find that the energy transfer efficiency is weakened, and the largest energy transfer efficiency is obtained when the resonant absorption peak of the Au NPs is farthest to the emission peak wavelength of CdSe/ZnS QDs. These results will be useful for the potential design of the high efficiency QDs optoelectronic devices.     

混合量子点器件电致发光的能量转移研究

在量子点的研究中,对于量子点光致发光研究报道较多,而量子点电致发光研究报道较少,特别是对于混合量子点电致发光器件中能量转移机理的研究未见报道,由于不同量子点之间的能量转移机理决定着器件的性能,为此本论文对该方面进行了研究.分别制备了单种量子点器件和混合器件,混合器件是利用红、绿、蓝三种量子点按照1:1的比例两两混合,做成结构为ITO/PEDOT:PSS/QDs/Al的器件.研究发现在一定电压范围内,单种量子点器件的发光强度随着电压增加持续上升,而混合量子点器件的发光出现了短波长下降,长波长上升的现象,表明当有外加电场时不同尺寸的量子点间产生了较高效率的能量转移.同时首次对混合量子点电致发光器件能量转移的各项参数进行了计算,得到了能量转移效率E、临界能量转移距离R0与外加电场的关系,对制备混合量子点电致发光器件具有指导意义.     

Manufacturing of Volumetric Glass–Based Composites with Single‐ and Double‐QD Doping

Quantum dot (QD)‐based light‐emitting materials are gaining increased attention because of their easily tunable optical properties desired for various applications in biology, optoelectronics, and photonics. However, few methods can be used to manufacture volumetric materials doped with more than one type of QD other than QD‐polymer hybrids, and they often require complicated preparation processes and are prone to luminescence quenching by QD aggregation and separation from the matrix. Here, simultaneous doping of a volumetric glass‐based nanocomposite with two types of QDs is demonstrated for the first time in a single‐step process using the nanoparticle direct doping method. Glass rods doped with CdTe, CdSe/ZnS, or co‐doped with both QDs, are obtained. Photoluminescence and lifetime experiments confirm temperature‐dependent double emission with maxima at 596 and 720 nm with mean lifetimes up to 16 ns, as well as radiative energy transfer from the short wavelength–emitting QDs to the long wavelength–emitting QDs. This approach may enable the simple and cost‐efficient manufacturing of bulk materials that produce multicolor luminescence with cascade excitation pumping. Applications that could benefit from this include broadband optical fiber amplifiers, backlight systems in LCD screens, high‐power LEDs, or down‐converting solar concentrators used to increase the efficiency of solar panels.     

庆大霉素与水溶性CdTe量子点的荧光共振能量转移作用

以巯基丙酸(mercaptopropionic acid,MPA)为稳定剂合成水溶性CdTe最子点(quantum dots,QDs),以CdTe QDs作为能量供体.庆大霉素(Gentamycin,GT)作为能垦受体,建立了荧光共振能量转移(fluorescence resonance energy transfer,FRET)体系.在690 nm处可见发射峰,半峰宽约10 nm,在一定范围内荧光强度与GT的含量旱线性关系,线性范围为2～20 mg·L-1,相关系数r=0.986 7.优化了不同的激发波长、pH、离子强度、时间和温度等凼素对反应的影响,并应用傅里叶变换红外光谱(Fourier transform infrared spectroscopy,FTIR)和高效液相色谱(high-performance liquid chromatography,HPLC)分别表征了化学结构和相对专一性.结果表明巯基丙酸的巯基中S原子和羧基中氧原子与纳米微粒表面的富Cd离子发生了配位作用,CdTe QDs与GT的耦合主要是通过量子点周围巯基丙酸羧基(-COOH)中的氧原子与GT的胺基(-NH2)形成分子问氧键实现的;GT与CdTe QDs的结合率为0.35:1.研究表明GT可以作为检测CdTe QDs标记牛血清白蛋白(bovine serum albumin,BSA)的荧光增敏剂,荧光强度值增强6倍,应用前景广阔.     

Hybrid light-emitting devices based on phosphorescent platinum(II) complex sensitized CdSe/ZnS quantum dots

We report on hybrid light-emitting devices based on the emission of phosphorescent sensitized colloidal CdSe/ZnS quantum dots (QDs). Emission lifetime measurements demonstrated that the energy transfer (ET) from square-planar platinum(II) complex [4-CF3-(NC^N^)PtC≡CC6H-4'-F] (NC^HN^=1, 5-bis(2'-pyridyl)benzene) (Pt-2) to QDs is more efficient than that from octahedral iridium(III) complex bis[(4,6-difluorophenyl)pyridinato-N, C2]-(picolinato)iridium (FIrpic). This different ET efficiency might be attributed to the different spatial structures between Pt-2 and FIrpic. Pure red emission with CIE coordinates of (0.66, 0.33) and maximum external quantum efficiency of 2.08% and white emission with power efficiency of 3.15 lm/W were realized at different concentrations of Pt-2 and QDs, respectively.     

基于Cu掺杂ZnInS和ZnCdS量子点的高显色性白光LED

利用胶体化学方法合成了发光波长可调的Cu掺杂量子点, 其波长范围可从绿光到深红光连续调节.通过将绿光ZnInS :Cu和红光ZnCdS :Cu量子点与蓝光GaN芯片相结合, 制备了高显色性的白光LED, 其流明效率为71 lm·W^-1, 色温为4 788 K, 显色指数高达94, CIE色坐标为(0.352 4, 0.365 1).通过测量Cu掺杂量子点的荧光衰减曲线, 发现不存在从绿光ZnInS :Cu到红光ZnCdS :Cu量子点的能量传递过程, 因为红光ZnCdS :Cu量子点在绿光波段没有吸收. 实验结果表明, Cu掺杂量子点有望应用于固态照明领域.     

Robust Aqueous Quantum Dots Capped with Peptide Ligands as Biomaterials: Facile Preparation,Good Stability,and Multipurpose Application

We have obtained robust peptide‐capped quantum dots (QDs) using a facile approach. The pentapeptide Cys‐Ala‐Leu‐Asn‐Asn (CALNN) is involved as the capping ligand, forming a self‐assembly monolayer on the surface of QDs, and solubilization of hydrophobic QDs in water is realized by simply mixing with the ligands in sodium hydroxide solution. All of the characterization results show that the prepared small‐sized QDs have excellent stability in acidic and high salt solutions. Additionally, the protein‐mimicking surface property of the peptide‐capped QDs eliminates the nonspecific cellular interaction, which in combination with the low cytotoxicity promises an ideal biomaterial in the future. Further functionalization and achievement of fluorescence resonance energy transfer (FRET) to graphene also display great potential for analytical applications.     

CdTe量子点-罗丹明B荧光共振能量转移法测定溶菌酶

合成了以硫代乙醇酸为稳定剂的CdTe量子点,以发射波长为530 nm的量子点为供体,罗丹明B为受体,建立一种以十六烷基三甲基溴化铵为介质的荧光共振能量体系检测溶菌酶含片中溶菌酶含量的方法。结果表明:在pH=5.0时,溶菌酶的浓度与共振能量转移效率降低值在2×10^-7~ 8×10^-6 mol·L^-1范围内呈线性关系,其线性方程为Y=306.07-13.85X,相关系数为0.991 0,检出限为2×10^-8 mol·L^-1,RSD为5.8%,平均回收率为101%(n=5)。     

Tunable and High Photoluminescence Quantum Yield from Self‐Decorated TiO2 Quantum Dots on Fluorine Doped Mesoporous TiO2 Flowers by Rapid Thermal Annealing

Herein a novel approach is reported to achieve tunable and high photoluminescence (PL) quantum yield (QY) from the self‐grown spherical TiO₂ quantum dots (QDs) on fluorine doped TiO₂ (F‐TiO₂) flowers, mesoporous in nature, synthesized by a simple solvothermal process. The strong PL emission from F‐TiO₂ QDs centered at ≈485 nm is associated with shallow and deep traps, and a record high PL QY of ≈5.76% is measured at room temperature. Size distribution and doping of F‐TiO₂ nanocrystals (NCs) are successfully tuned by simply varying the HF concentration during synthesis. During the post‐growth rapid thermal annealing (RTA) under vacuum, the arbitrary shaped F‐TiO₂ NCs transform into spherical QDs with smaller sizes and it shows dramatic enhancement (≈163 times) in the PL intensity. Electron spin resonance (ESR) and X‐ray photoelectron spectroscopy (XPS) confirm the high density of oxygen vacancy defects on the surface of TiO₂ NCs. Confocal fluorescence microscopy imaging shows bright whitish emission from the F‐TiO₂ QDs. Low temperature and time resolved PL studies reveal that the ultrafast radiative recombination in the TiO₂ QDs results in highly efficient PL emission. A highly stable, biologically inert, and highly fluorescent TiO₂ QDs/flowers without any capping agent demonstrated here is significant for emerging applications in bioimaging, energy, and environmental cleaning.     

Ab Initio Simulation of Charge Transfer at the Semiconductor Quantum Dot/TiO2 Interface in Quantum Dot‐Sensitized Solar Cells

Quantum dot‐sensitized solar cells (QDSSCs) have emerged as a promising solar architecture for next‐generation solar cells. The QDSSCs exhibit a remarkably fast electron transfer from the quantum dot (QD) donor to the TiO₂ acceptor with size quantization properties of QDs that allows for the modulation of band energies to control photoresponse and photoconversion efficiency of solar cells. To understand the mechanisms that underpin this rapid charge transfer, the electronic properties of CdSe and PbSe QDs with different sizes on the TiO₂ substrate are simulated using a rigorous ab initio density functional method. This method capitalizes on localized orbital basis set, which is computationally less intensive. Quite intriguingly, a remarkable set of electron bridging states between QDs and TiO₂ occurring via the strong bonding between the conduction bands of QDs and TiO₂ is revealed. Such bridging states account for the fast adiabatic charge transfer from the QD donor to the TiO₂ acceptor, and may be a general feature for strongly coupled donor/acceptor systems. All the QDs/TiO₂ systems exhibit type II band alignments, with conduction band offsets that increase with the decrease in QD size. This facilitates the charge transfer from QDs donors to TiO₂ acceptors and explains the dependence of the increased charge transfer rate with the decreased QD size.     

Acoustic phonon impact on the inter-Coulombic decay process in charged quantum dot pairs

ABSTRACT

Recently, highly accurate multi-configuration time-dependent Hartree electron dynamics calculations demonstrated the efficient long-range energy transfer inter-Coulombic decay (ICD) process to happen in charged semiconductor quantum dot (QD) pairs. ICD is initiated by intraband photoexcitation of one of the QDs and leads to electron emission from the other within a duration of about 150 ps. On the same time scale electronically excited states are reported to relax due to the coupling of electrons to acoustic phonons. Likewise, phonons promote ionisation. Here, the QDs' acoustic breathing mode is implemented in a frozen-phonon approach. A detailed comparison of the phonon effects on electron relaxation and emission as well as on the full ICD process is presented, which supports the previous empirical finding of ICD being the dominant decay channel in paired QDs. In addition the relative importance of phonon–phonon, phonon–electron and electron–electron interaction is analysed.     

Site-controlled quantum dots grown in inverted pyramids for photonic crystal applications

We report on the growth and optical properties of various configurations of sub-micron pitch dense arrays of pyramidal quantum dots (QDs) grown by organometallic chemical vapour deposition on patterned substrates. We show that the effective growth rate of these QDs is influenced by the ratio between the free {1 1 1}B area and {1 1 1}A exposed facets surrounding them. This provides a powerful technique for engineering the energy level structure of ordered QD arrays by means of geometrical patterning of the growth template. Such technique should be particularly useful for applications in photonic crystals incorporating QDs with tailored absorption and/or emission properties.     

Radiative energy transfer I. General equations

A set of equations is derived which makes possible to study the radiative energy transfer process whereby the photons emitted by the energy donor are absorbed by the energy acceptor and so increase the efficiency of the overall energy transfer. It is shown that the coefficients describing the radiative transfer which appear in the expressions for the intensities of the energy donor and the energy acceptor are not the same, due to the fact that part of the fluorescence absorbed by the acceptor comes from radiation which is not detected as donor emission when there is no acceptor present. The general equations derived are applied to two particular cases commonly considered: measurements in reflection, where the fluorescence emission is observed from the same face of the absorption and measurements in transmission where the fluorescence emission is observed from the opposite face of the cell.     

Valence band mixing of cubic GaN/AlN quantum dots

We study the spin purity of the hole ground state in nearly axially symmetric GaN/AlN quantum dots (QDs). To this end, we develop a six-band Burt-Foreman Hamiltonian describing the valence band structure of zinc blende nanostructures with cylindrical symmetry and calculate the effects of eccentricity variationally. We show that the aspect ratio is a key factor for spin purity. In typical QDs with small aspect ratio the ground state is essentially a heavy hole (HH) whose spin purity is even higher than that of InGaAs QDs of similar sizes. When the aspect ratio increases, mixing with light-hole (LH) and split-off (SO) subbands becomes important and, additionally, the ground state becomes sensitive to QD anisotropy, which further enhances the mixing. We finally show that, despite the large GaN hole effective mass, an efficient magnetic modulation is feasible in QDs with aspect ratio ~1, which can be used to modify the ground state symmetry and hence the optical spectrum properties.     

2018年5期 电子期刊

研究了不同Mn/Pb量比的Mn掺杂CsPbCl₃（Mn：CsPbCl₃）钙钛矿量子点的发光性质。Mn/Pb的量比增加引起的Mn²⁺发光峰的红移,被认为是来源于高浓度Mn²⁺掺杂下的Mn²⁺-Mn²⁺对。进一步研究了Mn：CsPbCl₃量子点的发光效率与Mn/Pb的量比之间的关系,发现随着量比达到5：1时,其发光效率明显下降。这种发光效率下降是由于Mn掺杂浓度引起的发光猝灭。Mn：CsPbCl₃量子点的变温发光光谱证实,随着温度的升高,Mn离子发光峰蓝移,线宽加宽,但其发光强度明显增加。     

FRET Studies of the Interaction of Dimeric Cyanine Dyes with DNA

Fluorescence Resonance Energy Transfer (FRET) is a powerful tool to determine distances between chromophores bound to macromolecules, since the efficiency of the energy transfer from an initially excited donor to an acceptor strongly depends on the distance between the two dye molecules. The structure of the noncovalent complex of double-strand DNA (dsDNA) with thiazol orange dimers (TOTO) allows FRET analysis of two intercalated chromophores. By intercalation of two different TOTO dyes we observe an energy transfer from TOTO-1 as donor and TOTO-3 as acceptor. In this manner we are able to determine the mean distance between two proximate TOTO molecules bound to dsDNA. Thus the maximum number of binding positions for this type of intercalation dyes in the dsDNA can be obtained. Furthermore the dependency of the acceptor emission on the donor concentration is analysed. The emission of TOTO-3 reaches a maximum when the acceptor-to-donor ratio is 1:10.     

Förster Energy Transfer in Arrays of Epitaxial CdSe/ZnSe Quantum Dots Involving Bright and Dark Excitons

Using time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Förster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole–dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Förster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.     

Donor bound excitons in wurtzite InGaN quantum dots: Effects of built-in electric fields

Within the framework of the effective-mass approximation and variational approach, we present calculations of the bound exciton binding energy, due to an ionized donor, in wurtzite In_xGa_1−xN/GaN strained quantum dots (QDs), considering three-dimensional confinement of the electron and hole in the QDs and the strong built-in electric field induced by the spontaneous and piezoelectric polarizations. Our results show that the position of the ionized donor, the strong built-in electric field, and the structural parameters of the QDs have a strong influence on the donor binding energy. The variation of this energy versus position of the donor ion is in double figures of milli-electron volt. Realistic cases, including the donor in the QD and in the surrounding barriers, are considered.