Absolute Quantifications of Oxy- and Deoxyhemoglobin Concentrations by Combination of Differentially Resolved Spectroscopy and Spatially Resolved Spectroscopy

This letter proposes a theoretical framework to calculate absolute concentrations of oxy- and deoxyhemoglobin using continuous-wave near-infrared spectroscopy. While previous methods on this topic require assumptions on constant blood volume, the proposed method does not. Equations for the absolute concentrations were derived from a combination of the modified Beer–Lambert equation and the theory of diffusion of photons in turbid media. The method has an advantage over and is theoretically consistent with previous methods. It needs yet to be evaluated in an experimental study.     

Time-Resolved Fluorescence Spectroscopy Study on the Photophysical Behavior of Quantum Dots

Room-temperature time-resolved luminescence measurements on single CdSe/ZnS quantum dots (QDs) are presented. Fluorescence emission spectra were recorded over periods of up to 30 minutes with a time resolution as small as 6 ms. For QDs in ambient air, a clear 30–40 nm blue shift in the emission wavelength is observed, before the luminescence stops after about 2–3 minutes because of photobleaching. In a nitrogen atmosphere, the blue shift is absent while photobleaching occurs after much longer times (i.e., 10–15 minutes). These observations are explained by photoinduced oxidation. The CdSe surface is oxidized during illumination in the presence of oxygen. This effectively results in shrinkage of the CdSe core diameter by almost 1 nm and consequently in a blue shift. The faster fading of the luminescence in air suggests that photoinduced oxidation results in the formation of non-radiative recombination centers at the CdSe/CdSeO_x interface. In a nitrogen atmosphere, photoinduced oxidation is prevented by the absence of oxygen. Additionally, a higher initial light output for CdSe/ZnS QDs in air is observed. This can be explained by a fast reduction of the lifetime of the long-lived defect states of CdSe QDs by oxygen.     

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.     

基于谷胱甘肽配体的ZnSe量子点对pH响应的时间分辨荧光光谱特性

当前,有关量子点pH响应方面的研究主要集中在含Cd(镉)类量子点,且都是研究其稳态荧光光谱对p H值的响应.然而,C d类量子点对生物体系具有一定的毒性,且稳态荧光光谱法由于受浓度等因素的影响具有一定的不稳定性,因此应用于生物体系中作为pH探针具有明显的缺点.基于以上分析,通过水相合成法,我们制备出了基于谷胱甘肽配体的...     

神经网络法研究多溴代二苯胺热力学性质

通过时间分辨光谱技术详细地研究了ZnCuInS/ZnSe/ZnS量子点的激子弛豫动力学. 基于速率分布模型,波长依赖的发射动力学表明本征激子、界面缺陷态中的激子、给-受体对态中的激子都会参与量子点的发光过程,整个发光过程主要依赖于给-受体对态发射. 瞬态吸收数据表明激发后本征激子和界面缺陷物种可能会同时出现,在高激发光强下,光强依赖的俄歇复合过程也存在于量子点中     

三维光谱学--二维红外光谱和时间分辨光谱

本文介绍了一类重要的光谱学分析方法-三维光谱学方法,对其中的时间分辨光谱和二维红外光谱作了详细的介绍,包括它们的基本原理、获取谱图的方法、谱图的性质等.介绍了二维红外光谱方法在光谱学分析中的一些应用领域.三维光谱分析方法已经成为光谱分析中重要的研究方法之一.     

Electron Tunneling Through Metallic Particles and Quantum Dots Connected to Ferromagnetic Leads

Electronic transport through small metallic particles and quantum dots, coupled by tunneling barriers to ferromagnetic electrodes, is studied theoretically. Nonequilibrium Green function techniques are used to calculate electric current and tunnel magnetorersistance due to rotation of the magnetic moments of external electrodes.     

Pitfalls and Their Remedies in Time-Resolved Fluorescence Spectroscopy and Microscopy

Time-resolved fluorescence spectroscopy and microscopy in both time and frequency domains provide very useful and accurate information on dynamic processes. Good quality data are essential in obtaining reliable parameter estimates. Distortions of the fluorescence response due to artifacts may have disastrous consequences. We provide here a concise overview of potential difficulties encountered under daily laboratory circumstances in the use of time- and frequency-domain equipment as well as practical remedies against common error conditions, elucidated with several graphs to aid the researcher in visual inspection and quality-control of collected data. A range of artifacts due to sample preparation or to optical and electronic pitfalls are discussed, as are remedies against them. Also recommended data analysis strategies are described.     

Scattering as a Quantum Metrology Problem: A Quantum Walk Approach

We address the scattering of a quantum particle by a one-dimensional barrier potential over a set of discrete positions. We formalize the problem as a continuous-time quantum walk on a lattice with an impurity and use the quantum Fisher information as a means to quantify the maximal possible accuracy in the estimation of the height of the barrier. We introduce suitable initial states of the walker and derive the reflection and transmission probabilities of the scattered state. We show that while the quantum Fisher information is affected by the width and central momentum of the initial wave packet, this dependency is weaker for the quantum signal-to-noise ratio. We also show that a dichotomic position measurement provides a nearly optimal detection scheme.     

Size‐Dependent Structural and Optical Characteristics of Glucose‐Derived Graphene Quantum Dots

It is of scientific importance to obtain graphene quantum dots (GQDs) with narrow‐size distribution in order to unveil their size‐dependent structural and optical properties, thereby further to explore the energy band diagram of GQDs. Here, a soft‐template microwave‐assisted hydrothermal method to prepare GQDs with diameters less than 5 nm ± 0.55 nm is reported. The size‐dependent photoluminescence (PL) quantum yield (QY) decay lifetime and electron energy loss spectroscopy (EELS) of the GQDs are studied systematically. The QY of the GQDs with an average diameter of 2 nm is the highest (15%) among all the samples investigated and the QY decreases with increasing diameter of the GQDs. The size‐dependence of the PL decay lifetime is also observed. The result suggests that spatial confinement effects related to radiative relaxation play an important role in the size‐dependent decay lifetime. A realistic energy band diagram of the GQDs is deduced from the experimental results.     

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.     

碳量子点/罗丹明B分子复合体系中的能量和电子转移过程研究

本文采用荧光光谱结合稳态和瞬态吸收光谱技术,研究了碳量子点(CQDs)/罗丹明B(RhB)分子复合体系o-CQDs/RhB和m-CQDs/RhB中的能量转移和电子转移过程以及它们之间的关系. 研究发现在能量转移效率为73.2%的o-CQDs/RhB体系中,电子转移过程可以忽略;而在能量转移效率低于33.5%的m-CQDs/RhB体系中,电子转移过程则较为显著. 在这个由碳量子点和染料分子组成的典型复合体系中所揭示的能量转移与电子转移过程之间的内联关系,将为与激子猝灭相关的应用提供有用的视角.     

ZnCuInS/ZnS量子点与Poly-TPD补偿发光光谱的研究

ZnCuInS/ZnS量子点是一种无重金属、“绿色”半导体纳米材料。在研究中,制备出尺寸为3.2 nm的ZnCuInS/ZnS核壳量子点,并说明它是施主-受主对复合发光。通过测量ZnCuInS/ZnS量子点的光致发光光谱,其发射峰值波长为620 nm、半宽度是95 nm的红光。同时,还制备出Poly-TPD有机薄膜,其发光光谱是峰值波长为480 nm的蓝光。所以,ZnCuInS/ZnS量子点和Poly-TPD发光颜色具有互补性。在ZnCuInS/ZnS量子点薄膜层上包覆一层poly-TPD薄膜后,二者发光颜色互补。在恰当的偏置电压下,可以得到较好的白光光谱。计算表明,其色坐标是(0.336,0.339),颜色指数是92。     

Bridging Two Worlds: Colloidal versus Epitaxial Quantum Dots

An overview is given of two distinct classes of semiconductor quantum dots, epitaxial and colloidal structures that have been studied intensely for more than 30 years by now, however, without large interconnection between the two involved research communities. The largely parallel and independent evolution of the two structure classes may be partly related to the origin of colloidal systems from chemistry, while epitaxial quantum dots have been addressed mostly by the physics community. These independent evolutions are somewhat surprising because the interest in optics‐related applications is shared by both communities. Here, a short summary of the development of the two structure classes, the present status of activities, and some perspectives for future developments are presented.     

ZnSe/SiO2半导体量子点玻璃的光谱特性

对采用溶胶凝胶法制备的ZnSe/SiO2半导体量子点玻璃的光谱性质进行了测试分析.UV-Vis透射光谱中观察到光吸收边相对于体相半导体有明显蓝移.稳态发射光谱(PL)中观察到ZnSe纳米晶体的位于蓝区的基本呈高斯分布的弱的最低激子发射峰、强而宽的表面态发光带以及对应杂质能级的三个锐峰发光.时间分辨荧光光谱(TRPL)中观察到发光效率高的最低激子发射峰,并测量其荧光衰减寿命,经尾部拟合为28.5 ps.同时,结合有效质量近似(EMA)模型,估计ZnSe纳米晶体的平均粒径介于2.45~3.60 nm之间,尺寸分布基本呈高斯型.     

飞秒时间分辨的能谱分析光电子显微镜：异质结超快载流子动力学测量

本文成功搭建了一套集成了能谱分析功能的时间分辨光电子显微镜系统(TR-PEEM),能够对电子密度分布进行时间分辨和能量分辨的成像.这套4D显微镜在空间、时间、能量多维度获取电子动力学信息提供了前所未有的手段.本文使用184 fs的时间分辨、150 meV的能量分辨和优于150 nm的空间分辨对半导体进行了测量,在Si(111)表面的Pb岛上获得了微区光电子能谱和能量分辨的TR-PEEM图像.实验结果表明,这套系统是进行异质结载流子动力学观察的有力工具,有助于在亚微米/纳米空间尺度和超快时间尺度上加深对半导体性质的理解.     

CdSeS量子点的光吸收谱亚结构和光致发光激发谱分析

用光致发光激发(PLE)谱分析吸收谱的亚结构。实验样品是共熔法制备的CdSeS量子点玻璃,量子点的生长时间分别为2h和4h,高分辨透射电子显微镜(HRTEM)分析得到样品中量子点的平均直径分别为3．6nm和3．8nm。在室温下对样品进行了光吸收谱和光致发光激发谱研究。光吸收谱显示了量子尺寸效应,光致发光激发谱中低能端有两个明显的峰。考虑价带简并以及电子与空穴之间的相互作用,通过理论分析和数值计算,得到1S3/2-1Se和2S3/2-1Se的跃迁能量及其随量子点半径的变化,由此确认光致发光激发谱中的两个峰分别为1S3/2-1Se和2S3/2-1Se跃迁。     

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.     

Noble Metal-Free Surface-Enhanced Raman Scattering Enhancement from Bandgap-Controlled Graphene Quantum Dots

Graphene quantum dot (GQD) represents an emerging noble metal-free surface-enhanced Raman scattering (SERS)-active nanomaterials for applications such as optoelectronics, chemical sensing, and biomedical imaging and therapy. However, it lacks a scalable method to synthesize GQD with selective structures and the fundamental understanding of their SERS enhancement through charge transfer between GQD and probe molecules. Here a bottom–up liquid-phase synthesis of colloidal GQDs with selective bandgaps using atmospheric-pressure microplasmas is reported. Electron microscopic and optical spectroscopic characterizations suggest that highly crystalline GQDs with nanographene structures can be synthesized with ambient conditions using microplasmas. Moreover, the bandgaps of GQDs are tuned from 2.8 to 3.18 eV by controlling the size of organosulfate micelles. Raman spectroscopic study demonstrates that the as-synthesized GQDs exhibit a unique quantum dot bandgap-dependent SERS enhancement property with an improved charge transfer between the GQD and probe molecules. This study provides an insight into the fundamental of semiconductor-enhanced Raman scattering of GQDs and scalable production of structure-controlled GQDs using plasma-activated chemistry.