Resonant Brillouin scattering by acoustoelectrically amplified phonons in CdSe

The dispersion of Brillouin scattering efficiency from the acoustoelectrically amplified phonon flux in CdSe has been measured in the range 1.37 to 1.65 eV. The dispersion curve shows enhancement and cancellation similar to those of GaAs, CdS and ZnO, and is in a good agreement with modified Loudon theory including exciton effects.     

Characterization of Cds clusters in zeolite-A grown in alkaline solution

CdS clusters were synthesized in A type zeolite by reaction in alkaline aqueous solution at temperatures from 30 to 70 °C. The optical properties of the samples were studied by diffuse reflectance and photoluminescence spectroscopy. Their crystalline structure and morphology were studied by X-ray diffraction and by transmission and scanning electron microscopy. We found that at lower temperatures the CdS clusters are encapsulated in the zeolite cages. We compared the properties of these clusters with those encapsulated in the cages of zeolites X and Y, prepared by similar methods. CdS clusters smaller than the CdS exciton diameter are also formed outside the cages in the zeolite matrix. The size of these clusters increases with temperature producing a red-shift of the absorption edge in the optical absorption spectra.     

Predicted new electromagnetic precursors and altered signal velocity in dispersive media

New optical precursors are predicted in media exhibiting “non-conventional” dispersion characteristics such as spatial dispersion, surface polaritons and surface plasmons. Numerical estimates are given for the exciton and surface polariton precursors in CdS, and surface plasmon in Al. The signal velocity increases in spatially dispersive media and is essentially constant throughout the “stop” gap. Measurement of these effects may provide new spectroscopic information regarding “non-conventional” dispersion.     

Light- and electron-beam-modulated reflectance of CdS single crystals

The optical reflectance of vapour grown CdS platelets was modulated by both the uv emission of an argon ion laser and an electron beam. After annealing the crystals in ultrahigh vacuum, the reflectance spectra exhibit sharp A and B exciton lines, which permit a precise measurement of position and halfwidth. Experimental proofs show that these spectra are caused by screening the coulomb interaction of the excitons by free carriers. Adsorption of oxygen onto the surface of the crystal does not influence the position and the halfwidth but only the peak height of the exciton lines.     

Center-of-mass quantization of excitons and Fabry–Perot modes of the polariton in ZnSe epilayers

Reflectance properties of ZnSe epilayers grown on GaAs substrates are studied at 80 K. Oscillation features are observed in the region of exciton resonance which are significantly different depending on the epilayer thickness L. For optically thin layers with thickness in the range of several tens of nanometer, reflectance oscillations appear above the light-hole (lh) exciton, while for optically thick layers with thickness in the range of a micrometer, reflectance oscillations appear between 1s and 2s excitons. These oscillations are interpreted as the quantized levels of the exciton center-of-mass motion in the lower branch of the polariton for optically thin layers and Fabry–Perot modes in the upper branch of the polariton for optically thick layers, respectively. The reflectance data are analyzed in the frame work of a dielectric function with a polariton dispersion.     

纳米CdS-磺化聚苯胺（SPAn）多层复合膜的光学特性研究

研究了利用层-层自组织生长法制备的磺化聚苯胺-CdS纳米晶体复合膜的光学特性.研究发现，随样品中CdS 纳米晶体尺寸的减小，量子尺寸效应明显增强；在紫外吸收谱中表现为吸收边出现了明显蓝移；在光致发光谱中，不仅激子直接复合产生的带边发射产生了蓝移，而且陷阱态复合产生的宽带发射也发生了蓝移.还发现样品经低温退火处理后，激子复合产生的带边发射显著增强，发射带宽随纳米尺寸的减小而变窄.这说明退火后CdS 纳米晶粒的有序性和均匀度显著增加. 关键词： CdS 纳米晶体 SPAn 吸收 发光     

Excitons in the preionization electric field of a Schottky barrier

The low-temperature (T=80 K) exciton reflectance spectra of CdS crystals in the electric field of a Schottky barrier are investigated. An anomalous Stark shift of a hydrogenic exciton state is detected in the preionization limit. An analysis of the spectra within the theory of a nonlocal dielectric response in a spatially inhomogeneous medium reveals the character of the subbarrier electric field distribution. Fiz. Tverd. Tela (St. Petersburg) 40, 879–880 (May 1998)     

Strong Interference Luminescence of Mixed Modes in the Neighborhood of the Critical Value of Exciton Decay

Optics and Spectroscopy - The results of a numerical calculation of the dispersion and luminescence spectra of mixed exciton modes of crystals of the CdS ( $${{A}_{{n = 1}}}$$ ) type are analyzed...     

The processes occurring in the surface region of CdS single crystals under electron bombardment,photoexcitation, and gas adsorption and their role in the 80 °K-exciton photoluminescence

Investigations have been carried out in the effect of 3–5 keV electron irradiation, intense photoexcitation, and gas adsorption on photoluminescent spectra of CdS single crystal platelets. CdS platelets subjected to electron bombardment were found to be very active for gas adsorption. The bound exciton emission is influenced by oxygen. A detailed study of the effect of the electron bombardment on the photoluminescence spectra is presented. The results indicate that correlation can be made between the behaviour of the electron bombardment-induced bound exciton emission and the electron processes occurring in the surface region of CdS single crystals. The changes in the photoluminescent spectra caused by the electron bombardment followed by the room temperature photoexcitation, have been interpreted in terms of surface photochemical effects.     

高纯CdS单晶生长及光学性质

本文报道用物理蒸气输运(PVT)法,通过对原料的提纯和控制组分蒸气压生长出高纯CdS单晶.叙述了控制晶体化学比的方法并通过比较CdS的激子光谱以评价材料的纯度.     

Size-dependent electronic and optical properties of an exciton in CdSe/CdS/CdSe/CdS multilayer spherical quantum dot

The electronic and optical properties of a single exciton in a CdSe/CdS/CdSe/CdS quantum dot is studied by using effective mass approximation with parabolic confinement. The Coloumbic interaction between electron and hole is included by Hartree potential. A self-consistent technique is used to calculate the energy eigenvalue and wavefunction of exciton. Based on this approximation we investigate the effect of core size, shell thickness, well width on exciton binding energy, absorption spectra, and oscillator strength. The results provide the tuning possibility of electronic and optical properties of multilayer quantum dot with layer thickness.     

CdTe/CdS核壳结构量子点超快载流子动力学

在水相合成CdTe以及CdTe/CdS核壳结构量子点基础上, 利用基于抽运-探测技术的瞬态差分透射技术研究了CdTe量子点以及不同CdS壳层厚度的CdTe/CdS量子点的最低激子能态的超快激发与弛豫动力学. 研究表明:相比于CdTe,CdTe/CdS量子点的电子空穴由于空间分离,其所需的激发时间要长于电子空穴空间重叠态所需要的激发时间.随着壳层厚度的增加, 量子点表面的钝化有效地减少了表面态相关弛豫机理,并延长相对应的弛豫时间.     

Ground state of excitons in quantum-dot quantum-well nanoparticles： stochastic variational method

Within the framework of effective mass approximation, the ground state of excitons confined in spherical core-shell quantum-dot quantum-well (QDQW) nanoparticles is solved by using the stochastic variational method, in which the finite band offset and the heavy (light) hole exciton states are considered. The calculated 1s_e－1s_h transition energies for the chosen CdS/HgS/CdS QDQW samples are in good agreement with the experimental measurements. Moreover, some previous theoretical results are improved.     

Photoreflection and photoconduction spectra of CdS crystals: Excitons in the electric fields of surface states

The exciton photoreflection spectra of CdS crystals are studied. It is found that the form of the exciton photoreflection spectrum is determined by a Stark shift of the exciton energy in the electric field of surface states. The dependences of the exciton photoreflection spectrum on temperature on the intensity and wavelength of the modulating radiation, and on the processes by which the photoreflection signal relaxes is determined. An energy scheme is proposed for the surface states which explains the observed effects of photoinduced changes in the surface field. A correlation is established between the exciton photoreflection spectrum and the form of the fine structure in the photoconductivity. Fiz. Tverd. Tela (St. Petersburg) 40, 875–876 (May 1998)     

Investigation of Dynamical Parameters of Exciton Confined in CdS Spherical Quantum Dots with a B-Spline Technique

Exciton energies as a function of radii of quantum dots in the range of 5-35 A are calculated based on effective mass approximation model with the B-spline technique and compared with experimental and other theoretical data for the CdS dots. This method leads to accurate and fast convergent exciton energy, which are in good agreement with experimental data in the whole confinement regime. The effect of penetration of wave function from the inside to the outside of the dots and the effect of dielectric constants are taken into account. The magnitudes of dynamical parameters are discussed. It is found that the different materials surrounding the CdS quantum dot affect not only the potential energy and Coulomb interaction energy of the system, but also the effective masses. The comparison shows that the effective mass approximation model can describe very well the quantum size effects observed experimentally on the exciton ground state energy.     

Vector classification, doublet splitting of exciton and biexciton subbands in crystals, and selection rules for transitions between them

The analysis of experimental data on absorption, reflection, luminescence in the region of exciton and biexciton phototransitions in CdS, including P-band structure, shows that there is doubled, contrary to known theory, number of free exciton and biexciton states. This discreapancy is removed in the vector model of these states presented in this paper. The selection rules for transitions between exciton (biexciton) states in crystals taking into consideration their L-T splitting are obtained. The spectra of stimulated FIR radiation on excitonic transitions in CdS, previously obtained experimentally, well fit to these selection rules.     

“反胶团法”合成的CdS半导体纳米粒子的光谱性质研究

反相胶束是指由介于油和水界面的表面活性剂分子, 稳定、且均匀分散于连续油介质中的微液滴。它可以作为“微反应器”合成性能优良的CdS粒子。文章研究了反相胶束的W值(W=[水]/[表面活性剂])、[Cd2+]与[S2-]的比例和Cd2+和S2- 离子的起始浓度对CdS纳米粒子发光特性均有明显影响。回流处理可以对CdS纳米粒子的表面进行修饰,可以使CdS粒子的缺陷发光减弱并消失而显著增强激子发射,同时可增大粒径使激子发射峰位红移,体现了明显的量子限域效应; 所得材料的室温最大荧光量子效率高达11%。     

Mesure du coefficient de decanalisation par un defaut d'empilement dans L'or

Defects in wurtzite single crystals of ZnS, ZnSe and CdS have been observed by means of both scanning and transmission electron microscopy. Application of the scanning technique to the observation of cathodoluminescence in these materials has demonstrated localized effects on the emission close to twin boundaries and stacking faults in the as-grown crystals, which may be interpreted in terms of changes in band gap at the defect. This method has also been applied to heavy ion bombarded crystals; in addition, transmission electron microscope studies have been made of these irradiated samples and the annealing behaviour of the radiation damage has been observed. Finally, in-situ optical absorption experiments have been carried out on samples irradiated at liquid nitrogen temperature, and effects on the characteristic exciton absorption have been noted.     

高密度激发下CdS单晶的自由激子发光

本文首次在77K温度的电致发光光谱上,观测到了自由激子和自由激子(Ex-Ex)散射的发射带P。根据半经典理论,得到CdS单晶在高激发密度下的激子有效温度高于晶格温度。并且在77K温度下,通过氮分子激光器3371Å谱线的激发,观察到了Ex-Ex散射的P带的受激发射现象。     

Brillouin scattering of “forbidden” polaritons in CdS

We use the results of Mahan and Hopfield's analysis of the B-exciton in CdS to derive the dispersion relations for three excitonic-polariton branches. Two of these polaritons are well known and have been investigated experimentally for the A-exciton in CdS by Winterling and Koteles. The third polariton is normally optically inactive but becomes allowed due to spin-orbit interaction which lifts the spin degeneracy of the exciton by an amount, øk, where k is the crystal momentum and ø is a coupling constant. We calculate the energy loss due to Brillouin scattering of polaritons between allowed and forbidden branches and predict that this loss should be experimentally observable. If seen, the value of ø could be more accurately determined and Mahan and Hopfield's conjectured model would be decisively confirmed.