The Electron－Hole Pair in a Single Quantum Dot and That in a Vertically Coupled Quantum Dot

The energy spectra of low-lying states of an exciton in a single and a vertically coupled quantum dots are studied under the influence of a perpendicularly applied magnetic field. Calculations are made by using the method of numerical diagonalization of the Hamiltonian within the effective-mass approximation. We also calculated the binding energy of the ground and the excited states of an exciton in a single quantum dot and that in a vertically coupled quantum dot as a function of the dot radius for different vaJues of the distance and the magnetic field strength.     

Integrated rate expression for the production of glucose equivalent in C4 green plant and the effect of temperature

A temperature-dependent integrated kinetics for the overall process of photosynthesis in green plants is discussed. The C₄ plants are chosen and in these plants, the rate of photosynthesis does not depend on the partial pressure of O₂. Using some basic concepts like chemical equilibrium or steady state approximation, a simplified scheme is developed for both light and dark reactions. The light reaction rate per reaction center (R′ ₁) in thylakoid membrane is related to the rate of exciton transfer between chlorophyll neighbours and an expression is formulated for the light reaction rate R′ ₁. A relation between R′ ₁ and the NADPH formation rate is established. The relation takes care of the survival probability of the membrane. The CO₂ saturation probability in bundle sheath is also taken into consideration. The photochemical efficiency (ϕ) is expressed in terms of these probabilities. The rate of glucose production is given by R _glucose = (8/3)(R′ ₁ v _L )ϕ(T) _g (T) ([G3P]/[P _i]² _leaf)_SS Q _{G3P→glucose} where g is the activity quotient of the involved enzymes, and G3P represent glycealdehyde-3-phosphate in steady state. A Gaussian distribution for temperature-dependence and a sigmoid function for de-activation are incorporated through the quotient g. In general, the probabilities are given by sigmoid curves. The corresponding parameters can be easily determined. The theoretically determined temperature-dependence of photochemical efficiency and glucose production rate agree well with the experimental ones, thereby validating the formalism.     

Spinless Excitons Implicit in SO(5) Theory

A pair of up-down operators are constructed explicitly for S.C.Zhang‘s SO(5) theory of high Tc superconductivity.From them two good quantum numbers are derived.The up-down operators are related to the spin-independent excitons which are not considered before.``     

Equilibrium and pre-equilibrium emissions in proton-induced reactions on <Superscript>203,205</Superscript>Tl

In this study, the excitation functions for the reactions ²⁰³Tl(p, n)²⁰³Pb, ²⁰⁵Tl(p, 3n)²⁰³Pb, ²⁰³Tl(p, 2n)²⁰²Pb, ²⁰⁵Tl(p, 4n)²⁰²Pb, ²⁰³Tl(p, 3n)²⁰¹Pb, ²⁰⁵Tl(p, 5n)²⁰¹Pb, ²⁰³Tl(p, 4n)²⁰⁰Pb and ²⁰⁵Tl(p, 6n)²⁰⁰Pb have been calculated using pre-equilibrium and equilibrium reaction mechanisms. Calculated results based on hybrid model, geometry-dependent hybrid model and cascade-exciton model have been compared with the experimental data.      

异价阳离子替代实现的金属卤化物CsCdCl3的明亮宽带绿色发光

全无机金属卤化物灵活多变的结构及优异的发光性能使其在固态光电子领域显示出重要的应用前景。本研究采用异价阳离子取代策略,用三价锑离子部分取代CsCdCl₃中的二价镉离子,促进自陷激子的产生,使CsCdCl₃∶Sb³⁺产生了明亮的宽带绿色发光,中心波长为530 nm。机理研究结果表明,CsCdCl₃∶Sb³⁺中相邻SbCl₆八面体被孤立,形成了低维电子构型,促进了Sb³⁺局域化,实现了量子效率最高为95.5%的高效发光。此外,尽管CsCdCl₃和RbCdCl₃均属于ACdCl₃(A为碱金属家族),但它们的晶体结构明显不同。RbCdCl₃属于正交晶系,空间群为Pnma;CsCdCl₃属于六方晶系,空间群为P6₃/mmc。CsCdCl₃的结构对称性大于RbCdCl₃,其...     

Cu2O半导体超微粒子的光学性质

本文研究了表面修饰的Cu2O半导体超微粒子的光学性质.在Cu2O超微粒子中未观察到显著的量子尺寸效应,但测量到很强的宽带光致发光,且随着激发波长变短,其发光带的峰位蓝移,发光带宽度增加.最后,分析了Cu2O超微粒子的宽带发光机制,并讨论了热处理对超微粒子的发光强度的影响.     

Use of pseudopotential towards time-evolution of a nonstationary state: Spatially localized excitation in a crystal

Pseudopotential is used as a formal operator to write the exact time-dependence of a pseudoexciton and hence that of an initial excitation spatially localized in a crystal. The exponential operator where pseudopotential occurs at the argument is readily evaluated using the property of projection operators. Migration of an initially localized excitation is of considerable experimental importance and can be of conceptual use since it should eventually generate the characteristics of a migrating exciton. From the formal time-dependence of a localized excitation, its spread with time can be calculated with relative ease. In a concurrent discussion, the previous work of Merrifield (1958) on the propagation of excitation is criticized and an error is pointed out. The spread, however, remains wavelike and is not dissipative in the absence of a collisional mechanism.     

Dynamics of long-living excitons in tunable potential landscapes

A novel method to experimentally study the dynamics of long-living excitons in coupled quantum well semiconductor heterostructures is presented. Lithographically defined top gate electrodes imprint in-plane artificial potential landscapes for excitons via the quantum confined Stark effect. Excitons are shuttled laterally in a time-dependent potential landscape defined by an interdigitated gate structure. Long-range drift exceeding a distance of at an exciton drift velocity is observed in a gradient potential formed by a resistive gate stripe.     

Détermination des structures désordonnée et ordonnée métastable du nickelocéne Ni(C5H5)2. Interprétation de l'évolution structurale comparée à celle du ferrocéne

Les données de diffraction X de la phase désordonnée du nickelocéne ont été enregistrées à 295K sur un diffractométre 4 cercles. La structure cristalline est isomorph de celle du ferrocéne: maille monoclinique, gruoups spatial statistiqe P2₁/a. Z=2. Utilisnt une méthod d'affinement en blocs moléculaires rigides et des calculs d’ énegie rétudiés. La Structure par 1’ existence de 4 états moléculaires possibles (anant un anlge interne de 20 ± 2[ddot] au lieu de 11.5° ± 1° pour le ferrocéne) symétriques deux à deux, sur chaque site cristallographique et formée de 2 types de clusters. L'emplilement moléculir de la phase ordonnée métastable du nickelocéne à 5 K a été déterminépar minimisation de son énergie éticulair. Les résultats obtenus (monoclinique, Z=2, à 101 K, indiquent quel l'évolution des phases désordonnées du nickelocéne et P2₁/a, configuration molécularie D ₅ d), Une interpétation de cette évolution differente fondée sur des hypothéses relatives à la dynamique du déordre est proposée.     

Ultimate Charge Extraction of Monolayer PbS Quantum Dot for Observation of Multiple Exciton Generation

Multiple exciton generation (MEG) has great potential to improve the Shockley-Queisser (S-Q) efficiency limitation for colloidal quantum dot (CQD) solar cells. However, MEG has rarely been observed in CQD solar cells because of the loss of carriers through the transport mechanism between adjacent QDs. Herein, we demonstrate that excess charge carriers produced via MEG can be efficiently extracted using monolayer PbS QDs. The monolayer PbS QDs solar cells exhibit α=1 in the light intensity dependence of the short-circuit current density J_sc (J_sc∝I^α) and an internal quantum efficiency (IQE) value of 100 % at 2.95 eV because of their very short charge extraction path. In addition, the measured MEG threshold is 2.23 times the bandgap energy (E_g), which is the lowest value in PbS QD solar cells. We believe that this approach can provide a simple method to find suitable CQD materials and design interface engineering for MEG.