PbS量子点光致荧光寿命的实验测量与确定

通过测量PbS量子点的吸收谱、时间分辨的荧光谱以及透射电子显微镜图,确定了不同粒径、不同温度、不同本底PbS量子点的光致荧光寿命,得到了描述第一吸收峰波长随量子点粒径变化的经验公式。结果表明,荧光寿命强关联于量子点粒径,可用负指数经验公式表达;荧光寿命弱依赖于温度;本底材料由于表面极化效应对荧光寿命也有影响。     

介电受限对CdSe量子点中受限激子的影响

在有效质量近似条件下,通过Wang和Zunger给出的CdSe量子点介电常量与其半径的关系,利用变分方法计算了该量子点中受限激子的基态能及束缚能.结果表明,在考虑量子点介电常量随尺度减小的变化以后,受限激子的束缚能增大,基态能降低,更接近实验值.同时,也讨论了量子点介电常量的尺度效应和表面极化效应对受限激子的影响. 关键词：     

ZnSe量子点敏化纳米TiO_2薄膜光电子特性研究

利用改进的直接吸附法制备核-壳ZnSe量子点敏化介孔掺镧nano-TiO_2复合薄膜.通过瞬态光伏和稳态表面光伏技术以及相应的检测手段,探测复合薄膜的微结构、光电子特性以及光生载流子在异质结薄膜中的传输机制.研究证实,包覆在Zn Se量子点外层的配体L-Cys主要通过其羧基与介孔nano-TiO_2表面未饱和的Ti原子键合,并完成量子点敏化复合薄膜的制备,由此实现对量子点在薄膜上沉积量的有效控制.实验结果表明:ZnSe量子点敏化nano-TiO_2薄膜的表面光伏响应出现在300—800 nm(紫外-可见-近红外)波长范围内,敏化后nano-TiO_2薄膜的光学带隙远小于敏化前薄膜以及ZnSe量子点的光学带隙;与具有p-型光伏特性的ZnSe量子点不同,敏化后薄膜显示出明显的n-型光伏特性,这将有利于光生电子由薄膜的外表面向光阳极基底方向迁移和注入;敏化后薄膜中光生载流子寿命、电子-空穴对分离速度和扩散长度的提高导致了瞬态光伏响应强度的增加和响应范围的扩大.     

半导体量子点的形状对受限激子的影响

在有效质量近似范围内,采用有限深势阱模型,考虑介电受限、计入表面极化效应的情况下,研究了球形、立方形半导体量子点的形状对受限激子的影响．结果表明量子点的形状效应不可忽略. 关键词：     

室温下正己烷本底中PbSe量子点的荧光寿命

利用透射电镜、近红外吸收谱、荧光光谱和时间分辨光谱等技术,在室温下测量离散在正己烷有机溶剂中,不同粒径的Pb Se量子点的吸收谱和荧光谱,给出了第一吸收峰和荧光峰随粒径变化的经验公式。通过对瞬态荧光衰减曲线的测量和分析,得到了Pb Se量子点的荧光寿命,其寿命与量子点的表面缺陷有关。在研究的粒径范围内,由于荧光跃迁仅为带间直接跃迁和仅为缺陷态跃迁两种极端情况,可得荧光寿命最宽分布区间位于1.44~11.96μs。荧光寿命弱关联于粒径,并随粒径的增大而呈线性减小。当Pb Se量子点的粒径为2.7~5.7 nm时,其实测的平均荧光寿命为7.17~6.72μs。     

介电受限对量子点中受限激子的影响

在有效质量近似下,采用有限深势阱模型研究了强受限制范围内,介电受限对球形,立方形半 量子点中受限激子的影响,结果表明在考虑表面极化效应以后,量子点的形状对受限激子的影响是不可忽略的。     

Mn掺杂Zn-In-S量子点的制备及发光性质研究

制备了Mn掺杂Zn-In-S量子点并研究了Zn/In的量比和反应温度对其发光性质的影响。在Mn掺杂的Zn-In-S量子点的发光谱中观测到一个600 nm发光带。通过改变Zn/In的量比,掺杂量子点的吸收带隙可从3.76 e V(330 nm)调谐到2.82 e V(440 nm),但600 nm发光峰的波长只有略微移动。这些掺杂量子点的最长荧光寿命为2.14 ms。当反应温度从200℃增加到230℃时,掺杂量子点的发光强度增加并达到最大值;而继续升高温度至260℃时,发光强度迅速减弱。此外,测量了Mn掺杂Zn-In-S量子点的变温发光光谱。发现随着温度的升高,发光峰位发生蓝移,发光强度明显下降。分析认为,Mn掺杂Zn-In-S量子点的600 nm发光来自于Mn2+离子的4T1和6A1之间的辐射复合。     

硅量子点发光的激活及其物理模型研究

在真空或惰性气体中制备的硅量子点发光很弱,硅量子点表面被氢较好钝化后的发光也不强.硅量子点表面的硅氧键或硅氮键能破坏这种钝化并在带隙中形成局域电子态,在局域电子态对应的激活中心有很强的发光.可以用这种方式构建发光物质,控制硅量子点表面的键合可获得不同波长的发光.在硅量子点的发光激活处理过程中,退火是很重要的环节.对于硅量子点发光激活的机理,本文给出了相应的物理模型.实验证明,在600和700 nm波长附近观察到了激活硅量子点的受激发光,在1500 nm到1600 nm波长范围观察到了激活硅量子点的较强发光.     

复介电常量双缺陷层的镜像对称光子晶体特性

利用传输矩阵法研究了两个复介电常量缺陷层镜像对称一维光子晶体的带隙结构和光传输特性。重点讨论了缺陷层的复介电常量的虚部为负值且光学厚度为λ0/4的情形时对传输特性的影响。研究发现:当在光子晶体的两端加入具有负虚部的复介电常量缺陷层后,多处出现了较强的透射峰增益。随着缺陷层复介电常量的虚部与实部比值的增加,各处透射峰增益变化规律不同。但中心波长处的缺陷膜的位置和高度不变。这为光子晶体同时实现多通道超窄带滤波器和不同放大倍数的光放大微器件的设计提供了理论基础。而在光子晶体的两端加入具有正虚部的复介电常量缺陷层后,各透射峰都出现了吸收现象,且随着其正虚部值I的增加,吸收越明显,这给光子晶体实现放大功能提供了理论指导。     

层状半导体WSe2的电子结构和各向异性光学性质研究

采用第一性原理密度泛函理论研究了六角层状晶体 WSe2 的电子结构和各向异性光学性质. 结果表明:WSe2 为间接带隙半导体, 带隙值为1 .44 eV, 略小于实验值(1 .51 eV) ; 价带和导带均主要由 W-5d 和Se-4p 电子构成, 在价带顶(0~2eV) 及导带底(1 .5 ~3.5 eV) , W-5d 和 Se-4p 电子杂化明显, 形成共价键. 介电函数的虚部和实部均表现出明显的各向异性,εi (xx ) 有一个明显的介电吸收峰, 而εi (zz ) 却有两个明显的介电吸收峰; WSe2 晶体对zz 光的低频透明区的能量范围几乎是xx 光的2 倍, 应用 WSe2 晶体的这一特性可以制备不同要求的偏振片.     

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.     

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.     

高斯分层介质粗糙面光波透射问题的微扰法研究

运用微扰法研究平面波入射分层介质粗糙面的光波透射问题,推出了不同极化状态的透射光波散射系数公式。采用高斯粗糙面来模拟实际的分层介质粗糙面,结合高斯粗糙面的功率谱导出了平面波入射高斯分层介质粗糙面的透射系数计算公式。通过数值计算得到HH极化透射系数随透射光波散射角变化的曲线,讨论底层介质介电常数、中间介质介电常数和厚度、粗糙面参数及入射光波长对透射系数的影响。数值计算结果表明：底层介质介电常数、中间介质介电常数和厚度、粗糙面参数及入射光波长对透射系数的影响是非常复杂的。     

The second-harmonic generation in parabolic quantum dots in the presence of electric and magnetic fields

The second-harmonic generation (SHG) coefficient for parabolic quantum dots (QDs) subject to applied electric and magnetic fields is theoretically investigated, within the framework of the compact-density-matrix approach and an iterative method. Numerical results are presented for typical GaAs/AlGaAs parabolic QDs. These results show that the radius of QD and the magnitude of electric and magnetic fields have a great influence on the SHG coefficient. And the peak shifts to the aspect of high energy when considering the influence of electric and magnetic fields. Moreover, the SHG coefficient also depends sensitively on the relaxation rate of the spherical QD system.     

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。     

Photoconduction in tunnel-coupled Ge/Si quantum dot arrays

The photoconduction in a tunnel-coupled Ge/Si quantum dot (QD) array has been studied. The photoconductance (PC) sign can be either positive or negative, depending on the initial filling of QDs with holes. The PC kinetics has a long-term character (10²?10⁴ s at T = 4.2 K) and is accompanied by persistent photoconduction (PPC), whereby the PC value is not restored on the initial level even after relaxation for several hours. These phenomena are observed upon illumination by light with photon energies both greater and smaller than the silicon bandgap. A threshold light wavelength corresponding to a long-term PC kinetics depends on the QD filling with holes. A model describing the observed PC kinetics is proposed, according to which the main contribution to the PC is related to the degree of QD filling with holes. By applying the proposed model to the analysis of PC kinetics at various excitation levels, it is possible to determine the dependence of the hopping conductance on the number of holes per QD. The rate of the charge carrier density relaxation exponentially depends on the carrier density.     

量子点背光技术的研究进展

量子点材料因具有发光波长可调,色度纯,量子效率高等优异特性而受到广泛关注,在光致发光高色彩显示方面有着巨大的应用潜力。本文综述了量子点背光技术的研究进展,主要对比了QDs On-Chip、QDs On-Surface及QDs On-Edge 3种量子点背光主流技术的基本原理及结构,并分析了它们在液晶显示领域的应用,未来前景及面临的挑战;然后介绍了几种新型的量子点背光技术,并对两种量子点背光新技术进行重点说明:一种是采用低温注塑成型工艺将量子点与高分子材料均匀混合为一体,用于制备直下式背光的量子点体散射型结构扩散板;另一种新技术是采用丝网印刷或喷墨打印工艺将量子点转印至导光板表面,形成应用于侧入式背光的量子点网点微结构导光板。这两种背光都具有制备工艺简单、成本低、生产效率高等特点,对高色域液晶显示的研究及发展意义深远。     

Extraordinary electron transmission through a periodic array of quantum dots

We study electron transmission through a periodic array of quantum dots (QD) sandwiched between doped semiconductor leads. When the Fermi wavelength of tunneling electron exceeds the array lattice constant, the off-resonant per QD conductance is enhanced by several orders of magnitude relative to the single-QD conductance. The physical mechanism of the enhancement is delocalization of a small fraction of system eigenstates caused by coherent coupling of QDs via the electron continuum in the leads.     

CdS_xSe_(1-x)/ZnS(核/壳)量子点的光谱截面及其掺杂光纤的传光特性

测量了不同组份比例x的CdS_xSe_(1-x)/ZnS(核/壳)量子点的吸收谱和发射谱,确定了量子点的吸收系数、吸收截面和发射截面.量子点吸收截面随粒径的增大而增大、随x的增大而减小.采用紫外固化胶,制备了掺杂浓度为0.1~5mg/mL的CdS_(0.4)Se_(0.6)/ZnS量子点光纤,测量了不同掺杂浓度量子点光纤中473nm泵浦功率的吸收衰减速率.吸收衰减速率和吸收截面弱关联于掺杂浓度.测量了光致荧光光谱强度随光纤长度和量子点浓度的变化.量子点光纤的光致荧光峰值强度随掺杂浓度和光纤长度变化而变化,且存在一个与最大峰值强度对应的饱和掺杂浓度和光纤长度.本文的实验结果有助于进一步构建新型的CdS_xSe_(1-x)/ZnS量子点增益型光电子器件.     

Optical anisotropy and the direction of polarization of exciton emissions in a semiconductor quantum dot:Effect of heavy-and light-hole mixing

The dependence of the directions of polarization of exciton emissions, fine structure splittings(FSS), and polarization anisotropy on the light-and heavy-hole(LH–HH) mixing in semiconductor quantum dots(QDs) is investigated using a mesoscopic model. In general, all QDs have a four-fold exciton ground state. Two exciton states have directions of polarization in the growth-plane, while the other two are along the growth direction of the QD. The LH–HH mixing does affect the FSS and polarization anisotropy of bright exciton states in the growth-plane in the low symmetry QDs(e.g., C_(2V),C_S, C_1), while it has no effect on the FSS and polarization anisotropy in high symmetry QDs(e.g., C_(3V), D_(2d)). When the hole ground state is pure HH or LH, the bright exciton states in the growth-plane are normal to each other. The LH–HH mixing affects the relative intensities and directions of bright exciton states in the growth-plane of the QD. The polarization anisotropy of exciton emissions in the growth-plane of the QD is independent of the phase angle of LH–HH mixing but strongly depends on the magnitude of LH–HH mixing in low symmetry QDs.