CdSe/HgSe/CdSe量子点量子阱(QDQW)晶粒的光学性质和电子结构

以CdSe纳米晶体为核,用胶体化学的方法,通过化学替代反应,获得了不同阱层或不同垒层的CdSeHgSeCdSe量子点量子阱(QDQW)晶体.紫外可见光吸收谱研究表明,通过调节QDQW中间HgSe阱层的厚度从0.9nm至0,可以调节QDQW颗粒的带隙从1.8变化至2.1eV,实现QDQW纳米晶体的剪裁.光致荧光(PL)谱研究显示,QDQW形成后,CdSeHgSe纳米颗粒表面态得到钝化,显现出发光强度加强的带边荧光峰.利用有效质量近似模型,对QDQW晶粒内部电子的1s—1s态进行了估算,估算结果总体趋势与实验数据相符 关键词： 量子点量子阱晶体 能带剪裁 加强的带边荧光峰     

Well width‐dependent electron Raman scattering in ZnS/CdSe cylindrical quantum dot quantum well

Electron Raman scattering (ERS) is investigated in ZnS/CdSe cylindrical quantum dot quantum well (QDQW). The differential cross section (DCS) is calculated as a function of the scattering frequency and the sizes of QDQW. Single parabolic conduction and valence bands are assumed. Different scattering configurations are discussed and the selection rules for the processes are also studied. Singularities in the spectrum are found and interpreted. The ERS studied here can be used to provide direct information about the electron band structure of these systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Bound polaron in quantum dot quantum well structures

The problem of bound polarons in quantum dot quantum well (QDQW) structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical (LO) and surface optical (SO) modes are derived in the framework of the dielectric continuum approximation. The electron--phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numerical results reveal that there exist three branches of eigenfrequencies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.     

极化子效应对ZnS/CdSe柱型核壳量子点简并四波混频过程的影响

理论计算了带有极化子效应的ZnS/CdSe柱型核壳结构量子点简并四波混频的三阶极化率.在有效质量近似下,采用无限深势阱模型,导出了带有极化子效应的柱型量子点的三阶非线性光学极化率的解析表达式,解三维薛定谔方程得到电子的本征能量和波函数.分析了电子-LO声子和电子-IO声子相互作用对ZnS/CdSe核壳结构量子点简并四波混频的三阶极化率的影响.结果表明,当量子点尺寸一定时,带有极化子效应的χ(3)DFWM比没有极化子时的三阶极化率提高了近3个数量级,并且电子-LO声子的影响比电子-IO声子的影响大得多;当固定核壳量子点的阱宽而内外半径发生变化时,χ(3)DFWM的峰值随之变化,而且极化子效应影响的大小也随之发生变化.     

Parameter-dependent photon echo induced in CdSe/ZnS quantum dot quantum well

The two pulse photon echo (2PPE) phenomena induced by the 1s-1s electronic transition in CdSe/ZnS quantum dot quantum well (QDQW) has been studied by employing semiconductor Bloch equations. The energy eigenvalues and eigenfunctions of electrons and holes have been obtained by solving the stationary Schrödinger equation under effective-mass approximation. The Coulomb interaction, which changes with the size variation of QDQW, has been calculated and analyzed as a perturbation. The variations of the electric transition dipole moment and the energy interval with the changing of the size and structure of the QDQW have also been obtained. It has been shown from the numerical calculation results that the efficiency of 2PPE can be controlled by the variation of the size and structure of the QDQW and the mechanism has been explained in terms of the quantum size confined effect (QSCE) theory.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子隧穿过程

用室温光致发光谱和飞秒脉冲抽运探测方法对不同垒宽的ZnCdSe量子阱/ZnSe/CdSe 量子点新型耦合结构中激子隧穿过程进行研究，观察到激子从量子阱到量子点的快速隧穿过 程.在ZnSe垒宽为10nm, 15nm, 20nm时，测得激子隧穿时间分别为1.8ps, 4.4ps, 39ps. 关键词： ZnCdSe量子阱 CdSe量子点 激子 隧穿     

四波混频与瑞利散射场的干涉现象

介绍在半导体量子阱的飞秒激光四波混频实验中观测到的新的干涉现象.分析表明,实验曲线中的相干振荡来自样品的瑞利散射与四波混频信号的干涉.运用此干涉模型进行了理论模拟,所得结果与实验符合得很好,并由此较准确地得到了介质的退相时间为44 fs. 关键词： 量子阱 四波混频 瑞利散射     

Electronic structure of two-electron quantum dot with parabolic potential

In this study, we investigate the parabolic potential effects on the ground and excited energy states of two-electron quantum dot with impurity inside an infinite spherical confining potential well. The wave function and energy eigenvalues were calculated using a modified variational optimization procedure based mainly on quantum genetic algorithm and Hartree–Fock–Roothaan method. The results show that the parabolic potential and impurity charge have a strong effect on the energy states and ionization energies. It is worth pointing out that as impurity charge increases, the ionization energy rises, but the ionization dot radius decreases. On the other hand, as parabolic potential increases, the ionization energy decreases, but the ionization dot radius increases.     

近简并四波混频相位共轭介质中的光强分布

从求解耦合波方程出发，详细研究了非线性光学介质中由近简并四波混频所产生的相位共轭过程。以上述波方程的解为基础，给出作为混频结果的反射传播相位共轭波沿介质轴向的光强分布，得到比以往文献中所报道的更为精确的结果，从而为选择工作物质的最佳尺寸提供了理论依据。     

Fluorescence correlation spectroscopy of CdSe/ZnS quantum dot optical bioimaging probes with ultra-thin biocompatible coatings

The colloidal stabilities and emission properties of CdSe/ZnS quantum dot (QD) optical probes capped with a variety of thin, hydrophilic surface coatings were studied using confocal fluorescence correlation spectroscopy. These coatings are based on mercaptoethanol, mercaptopropionic acid (with and without conjugated aminoethoxyethanol), lipopolymers (DSPE-PEG2000), cysteine (Cys), and a variety of Xaa-Cys dipeptides. The study shows that QDs with thin hydrophilic coatings can be designed that combine good colloidal stability and excellent emission properties (brightness). Furthermore, there is a general correlation between colloidal stability and brightness. The experiments reported illustrate that QDs with multiple types of thin coatings can be created for optical imaging applications in a biological environment while also maintaining a size below 10 nm.     

基于氧化镁晶体中级联四波混频过程的紫外飞秒光脉冲产生

紫外波段飞秒激光脉冲是研究超快化学和超快物理相关过程的重要工具,实现波长可调谐的宽带紫外飞秒光脉冲将有助于推动超快动力学及相关领域的研究.本文报道了以两束400 nm的飞秒光脉冲作为级联四波混频的抽运源,在氧化镁晶体中产生9阶频率上转换和5阶频率下转换边带信号的实验结果.边带波长范围从350 nm到450 nm连续可调谐,这些边带信号的发散角和波长与级联四波混频理论预测结果吻合.紫外边带相对于入射光的整体转化效率约为1.2%.同时,高阶边带的光谱形状呈现高斯型,其谱宽理论上支持傅里叶转换极限脉宽为20—50 fs.本文展示了一种高效产生波长可连续调谐的紫外飞秒光脉冲的便捷方法,为基于紫外超短脉冲的相关研究提供了有效工具.     

球形ZnS/CdSe/ZnS核壳壳量子点的三阶极化率参量相关特征

在有效质量近似下,利用量子力学的密度矩阵理论,采用无限深势阱模型导出了三层球型量子点的三阶非线性光学极化率(自聚焦)的解析表达式.通过数值计算,分析了ZnS/CdSe/ZnS球型核壳结构量子点的三阶极化率(自聚焦)与量子点尺寸和入射光频率之间的关系.结果显示,量子点尺寸增大时,自聚焦效应三阶极化率(自聚焦)的峰值高度增大,峰值位置红移.本文的讨论为实验研究和实际应用提供了理论依据,对于光电器件的研究和改进有参考价值.     

Characteristics of wavelength conversion of short optical pulses in quantum dot semiconductor optical amplifiers

The characteristics of short optical pulse four-wave mixing (FWM) and amplification in quantum dot semiconductor optical amplifiers (QD-SOAs) are investigated taken into account the effect of the multi-discrete QD energy levels. Different saturation and recovery response for the electron and hole states are observed, which is attributed to different energy spacing between the energy states. We found that the 3 dB saturation energy of QD-SOA depends on the pulse width for short input pulses. Also, the optimum time delay between the probe and pump pulses in QD-SOAs, which provides maximum FWM efficiency in QD-SOAs, is smaller than the optimum delay in quantum well SOA.     

CdSe/ZnS量子点在倏逝波光纤pH传感中的应用

将新型量子点荧光传感技术与光纤倏逝波传感技术相结合,发展了一种基于量子点荧光效应并结合倏逝波传导进行溶液酸碱度检测的新型传感技术,具有灵敏度高、检测速度快、便于微环境检测、可实现远程探测、实时监测和原位分析等特点。详细介绍了用于倏逝波传感的锥柱组合型光纤荧光探头的制备方法,量子点在光纤探头表面的修饰流程,光谱与强度两种光纤pH传感平台的建立,并分别从响应范围、线性度、重复性和稳定性等方面对CdSe/ZnS量子点应用于光纤pH传感进行了评价。结果表明,在pH值为2~12的范围内,CdSe/ZnS量子点的荧光光谱信号的峰位在强酸和强碱的情况下都会产生红移,且红移量随pH值的变化呈线性关系,其量子点荧光强度信号随pH值的减小呈线性降低关系,通过在强酸和强碱下交替测试的实验表明其具有较好的重复性,利用荧光强度传感平台进行实时监测的实验表明其具有较好的稳定性。因此,将CdSe/ZnS量子点用于倏逝波光纤pH传感具有可行性,在生物化学、环境监测、医学临床、食品安全等领域的pH值测量方面有着广泛的应用前景。     

Band structure and impurity effects on optical properties of quantum well and quantum dot infrared photodetectors

We examined theoretically band structure and discrete dopant effects in the quantum well infrared photodetector (QWIP) and the quantum dot infrared photodetector (QDIP). We find that in QWIPs discrete dopant effects can induce long wavelength infrared absorption through impurity assisted intra-subband optical transitions. In QDIPs, we find that a strategically placed dopant atom in a quantum dot can easily destroy the symmetry and modify the selection rule. This mechanism could be partially responsible for normal incidence absorption observed in low-aspect-ratio quantum dots.     

有效质量差异和电场对GaN/AlxGa1-xN球形量子点电子结构的影响

用平面波展开法对GaN/Al_xGa_1-xN球形量子点中类氢杂质态能级随量子点半径、Al组分以及结合能随Al组分的变化规律进行了详细讨论.计算了量子点内外有效质量差异对杂质态能级和结合能的修正,结果表明对于Al组分较高的GaN/Al_xGa_1-xN球形量子点,电子有效质量差异对杂质能级和结合能的修正不能忽略.考虑电子有效质量差异后,进一步具体计算了杂质结合能随量子点半 关键词： 球形量子点 平面波展开法 有效质量     

双电子二维量子点基态能量的计算

分别利用微扰法、精确的对角化方法和变分法计算了双电子二维量子点的基态能量,与早期无约束的哈特利-福克研究结果比较,发现三参量的变分波函数是基态的极好表征.     

Unraveling the electronic structure of transition metal dimers using resonant four‐wave mixing

The potential of two‐color resonant and degenerate four‐wave mixing spectroscopy for investigations of the complex spectra of transition metal dimers is explored. Two‐color resonant and degenerate four‐wave mixing spectroscopy scans of the well‐known A‐X and B‐X transitions in Cu₂ are reported and compared with previous experimental data obtained from standard single‐resonance techniques. The selectivity of the method is shown to enable the measurement of isotopologue pure spectra without the need for isotopically enriched metal targets. Specific subsets of the rovibronic structure are separated in a congested spectral region of overlapping transitions. The sensitivity of the method compares satisfactorily with linear spectroscopic methods such as laser‐induced fluorescence and cavity ring‐down. A new laser vaporization source for the production of transition metal dimers and clusters has been constructed. The new design aims for a high number density and maximum possible shot‐to‐shot stability. The possibilities of further applications of non‐linear four‐wave mixing spectroscopy to Cu₂ and other transition metal dimers are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Theory of pulse propagation and four-wave mixing in a quantum dot semiconductor optical amplifier

A theory, combining the relations of pulse traveling into quantum dot (QD) semiconductor optical amplifier (SOA) with the four-wave mixing (FWM) theory in these SOAs, is developed. Carrier density pulsation (CDP), carrier heating (CH), and spectral hole burning (SHB) contributions on FWM efficiency are discussed. Effect of QD ground state and wetting layer are included. An additional parameter appears in the gain integral relation of QD SOAs. An equation formulating pulses in the QD SOAs is introduced. We have found that FWM in QD SOAs is detuning and is pulse width dependent. For short pulses, CH is dominant at high detunings (10–100 GHz) while at higher detunings (>100 GHz) the SHB is the dominant one. Undesired paunch behavior is shown in QD SOAs then, CDP must be reduced.