Graphene Quantum Dots

Graphene quantum dots (GQDs) are nanometer‐sized fragments of graphene that show unique properties, which makes them interesting candidates for a whole range of new applications. This review article gives an overview of the synthesis, properties and applications of GQDs. Synthesis methods discussed include top‐down and bottom‐up approaches. Properties such as luminescence up‐ and down‐conversion have been used in applications ranging from energy conversion to bio‐analytics. This article provides an overview of the state‐of‐the‐art and highlights promising findings as well as potential future directions of the research field.     

Photochromic Quantum Dots

Russian Physics Journal - Results of fundamental and applied research in the field of creating photochromic core-shell type nanoparticles in which semiconductor nanocrystals – quantum dots...     

Single-Photon Emission from InAs/AlGaAs Quantum Dots

The results of investigation of the radiative characteristics of heterostructures with InAs/AlGaAs quantum dots (QDs) grown by molecular beam epitaxy have been presented. The properties of single QDs were determined by spectroscopy of micro-photoluminescence in cylindrical mesa-structures with a diameter of 200–1000 nm or columnar microresonators with distributed Bragg mirrors. The single-photon nature of the radiation is confirmed by measurements and analysis of the second-order correlation function g²(τ) in a wide spectral range from 630 to 730 nm.     

Assessing Carrier Recombination Processes in Type‐II SiGe/Si(001) Quantum Dots

In this work, it is shown how different carrier recombination paths significantly broaden the photoluminescence (PL) emission bandwidth observed in type‐II self‐assembled SiGe/Si(001) quantum dots (QDs). QDs grown by molecular beam epitaxy with very homogeneous size distribution, onion‐shaped composition profile, and Si capping layer thicknesses varying from 0 to 1100 nm are utilized to assess the optical carrier‐recombination paths. By using high‐energy photons for PL excitation, electron‐hole pairs can be selectively generated either above or below the QD layer and, thus, clearly access two radiative carrier recombination channels. Fitting the charge carrier capture‐, loss‐ and recombination‐dynamics to PL time‐decay curves measured for different experimental configurations allows to obtain quantitative information of carrier capture‐, excitonic‐emission‐, and Auger‐recombination rates in this type‐II nano‐system.     

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.     

水溶胶CdSe/CdS核/壳结构纳米晶制备及光学性质的研究

以巯基乙酸为稳定剂在水溶液中合成了水溶胶CdSe/CdS核/壳结构的量子点,利用X射线粉末衍射(XRD)和X射线光电子能谱(XPS)对量子点结构进行了表征;并对化学组成和尺寸分布进行了研究。通过紫外-可见吸收光谱、激发光谱与发射光谱研究了它们的发光特性。     

ZnCuInS/ZnSe/ZnS量子点发光光谱特性的研究

ZnCuInS/ZnSe/ZnS量子点是一种无毒,无重金属的“绿色”半导体纳米材料。在研究中,制备了三种尺寸的ZnCuInS/ZnSe/ZnS核壳量子点,其直径分别为3.3,2.7,2.3 nm。通过测量不同尺寸的ZnCuInS/ZnSe/ZnS量子点的光致发光光谱,其发射峰值波长随尺寸的减小而蓝移。其吸收峰值波长和发射峰值波长分别是510,611(3.3 nm),483,583(2.7 nm)以及447,545 nm(2.3 nm)。ZnCuInS/ZnSe/ZnS量子点具有显著的尺寸依赖效应。ZnCuInS/ZnSe/ZnS量子点的斯托克斯位移分别为398 meV(3.3 nm),436 meV(2.7 nm)以及498 meV(2.3 nm),这样大的斯托克斯位移证明,ZnCuInS/ZnSe/ZnS量子点的发光机制与缺陷能级有关。同时,对直径为3.3 nm的ZnCuInS/ZnSe/ZnS量子点进行了温度依赖的光致发光光谱的测量,当温度为15～90 ℃时,该量子点发射峰值波长随温度的升高而红移,发光强度随温度的升高而降低,说明ZnCuInS/ZnSe/ZnS量子点是以导带能级与缺陷能级之间跃迁为主的复合发光。     

CdSe/CdS/ZnS 量子点体系中的超快载流子动力学

利用飞秒泵浦探测技术对CdSe/CdS/ZnS量子点体系中的超快载流子动力学过程进行了研究. 通过选择不同波长的泵浦光分别激发样品壳层和核层,研究了载流子在壳层和核层中的超快动力学过程. 实验结果表明,载流子在CdS壳层导带中弛豫过程非常迅速(约130 fs),时间明显短于载流子在CdSe核层导带中的弛豫时间(约400 fs). 实验中也发现在CdS壳层和CdSe核层的分界面存在一定量的缺陷态.     

Electron Spins in Quantum Dots as Quantum Bits

The creation, coherent manipulation, and measurement of spins in nanostructures open up completely new possibilities for electronics and information processing, among them quantum computing and quantum communication. We review our theoretical proposal for using electron spins in quantum dots as quantum bits, explaining why this scheme satisfies all the essential requirements for quantum computing. We include a discussion of the recent measurements of surprisingly long spin coherence times in semiconductors. Quantum gate mechanisms in laterally and vertically tunnel-coupled quantum dots and methods for single-spin measurements are introduced. We discuss detection and transport of electronic EPR pairs in normal and superconducting systems.     

上转换发光量子点

光子上转换是一种重要的非线性反斯托克斯发光现象,在激光、显示、光伏、信息安全以及生物成像与诊疗等领域具有应用前景.与研究较多的有机分子三重态-三重态湮灭和稀土掺杂纳米颗粒上转换发光材料相比,上转换量子点可以在宽光谱激发范围内实现上转换发光,具有频谱吸收宽、发光效率高、近红外可吸收、能带可调、尺寸小以及稳定性高等特点,引...     

Charged-Exciton Complexes in Quantum Dots

It is known experimentally that stable charged-exciton complexes can exist in low-dimensional semiconductor nanostructures. Much less is known about the properties of such charged-exciton complexes since three-body problems are very difficult to be solved, even numerically. Here we introduce the correlated hyperspherical harmonics as basis functions to solve the hyperangular equation for negatively and positively charged excitons (trions) in a harmonic quantum dot. By using this method, we have calculated the energy spectra of the low-lying states of a charged exciton as a function of the radius of quantum dot. Based on symmetry analysis, the level crossover as the dot radius increases can be fully explained as the results of symmetry constraint.``     

Charged-Exciton Complexes in Quantum Dots

It is known experimentally that stable charged-exciton complexes can exist in low-dimensional semiconductor nanostructures. Much less is known about the properties of such charged-exciton complexes since three-body problems are very difficult to be solved, even numerically. Here we introduce the correlated hyperspherical harmonics as basis functions to solve the hyperangular equation for negatively and positively charged excitons (trions) in a harmonic quantum dot. By using this method, we have calculated the energy spectra of the low-lying states of a charged exciton as a function of the radius of quantum dot. Based on symmetry analysis, the level crossover as the dot radius increases can be fully explained as the results of symmetry constraint.     

掺杂PbSe/PVA量子点的光致聚合物全息特性

通过原位合成法以聚乙烯醇辅助合成了6.5nm、10nm和15nm的PbSe量子点,研究了掺杂PbSe量子点的光致聚合物的全息特性.将三种尺寸的PbSe量子点按不同浓度分别掺入光致聚合物中,制成无机-有机复合型光致聚合物膜,并对其全息性能进行研究.复合聚合物膜的UV-Vis吸收光谱表明掺入的PbSe量子点并未与聚合物中的有机组分发生化学反应.采用氩氪离子激光器输出的647nm红光研究了复合聚合物膜的透过率和全息记录光栅的布喇格偏移与衍射效率.透过率曲线表明PbSe量子点在复合聚合物膜中分散良好,膜表面均匀.由于PbSe量子点在聚合物链中起支撑作用,复合聚合物膜在全息记录过程中不易发生形变,从而增加了聚合物膜的抗缩皱能力.衍射效率曲线表明掺入PbSe量子点的复合聚合物膜的衍射效率比未掺杂的有所提高.此外,体系存在一个最优值,当掺入平均粒径为10nm且浓度为3.6×10-6 mol/L的PbSe量子点时,样品的透过率达到84%,衍射效率从67.2%提升到89.7%,缩皱率降低到0.8%,极大提高了材料的全息性能.     

Ultrafast Saturable Absorption of Core/Shell Colloidal Quantum Dots

Ultrafast saturable absorption (SA) materials that are capable of blocking the optical absorption under strong excitation have extensive applications in photonic devices. This work presents core/shell colloidal quantum dots (CQDs) which have the quantized energy levels, excellent band gap tunability, and possess significant SA performance. When the band gap is close to the pump pulse energy, the CQDs show significant resonant SA response. At the same excitation conditions, the core/shell CQDs dispersions show better SA response than graphene dispersions, and comparable to the recently reported molybdenum disulfide. The carrier dynamics of the SA of the CQDs is analyzed systematically. The research has also found that the two‐photon absorption of the CQDs show nearly cubic power law of the band gap, while the SA performance keeps almost the same in the nonresonant regime. Further, superior passive Q‐switched laser behavior is observed using the CQDs as a saturable absorber. The results directly reveal the physical processes of this basic problem and broaden the applications of CQDs in photonic devices.     

InAs/GaAs单量子点中电子/空穴自旋弛豫

利用分子束外延制备了三种类型量子点样品,它们分别是:未掺杂样品、n型Si调制掺杂样品和p型Be调制掺杂样品。在5 K温度下,采用共聚焦显微镜系统,测量了单量子点的光致发光谱和时间分辨光谱, 研究了单量子点中三种类型激子(本征激子、负电荷激子和正电荷激子)的电子/空穴自旋翻转时间。它们的自旋翻转时间常数分别为: 本征激子的自旋翻转时间约16 ns, 正电荷激子中电子的自旋翻转时间约2 ns, 负电荷激子中空穴的自旋翻转时间约50 ps。     

ZnCuInS/ZnS量子点光致发光温度依赖性研究

ZnCuInS/ZnS量子点是一种无重金属"绿色"半导体纳米材料。制备出了直径为2.9nm的ZnCuInS/ZnS核壳量子点。从ZnCuInS/ZnS量子点的吸收及光致发光光谱中可以看到,量子点的斯托克斯位移为410meV。这样大的斯托克斯位移表明,ZnCuInS/ZnS量子点的复合机制与缺陷能级有关。研究并计算了在辐射及非辐射驰豫过程的(Huang-Rhys)因子及平均声子能量。结果表明在50~373K范围内,能量带隙的变化以及光致发光光谱的增宽是分别由光从能带边缘向缺陷能级跃迁及载流子声子耦合导致的。