Radiative recombination in stressed superlattices

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 160–163, May–June, 1995.     

Radiative corrections to the polarizability of helium

The complete alpha(3) QED correction to the helium atom polarizability is computed assuming an infinite nuclear mass and found to be equal to 0.000030666(3) a.u., with the contribution from the electric-field dependence of the Bethe logarithm amounting to 0.000000193(2) a.u. After including the alpha(2) and alpha(3) corrections for the nuclear recoil and the leading part of the alpha(4) QED correction, we find that the molar polarizability of 4He is 0.51725419(9)(4) cm(3)/mol. The first of the two error bounds is dominated by the uncertainty of alpha(4) and higher-order QED corrections and the second reflects the uncertainty of the Avogadro constant.     

氦原子双电子激发态的辐射光谱

利用同步辐射高等光源激发氦原子测量了在能量范围63～66 eV的双电子激发态的真空紫外辐射光谱,给定了sp,2n+(n至26),sp,2n-(n至24)和2pnd(n至9)的氦原子双电子激发态能级位置,获得了一些对认识原子双电子激发态过程中辐射跃迁的影响有价值的结果.     

Radiative recombination in hydrogenated amorphous silicon

Hydrogenated amorphous silicon exhibits efficient optical transitions across a gap larger than that of crystalline Si. Hydrogen passivates the dangling bonds and endows the material with a reduced number of non-radiative recombination centers. A gap widening has been observed in other hydrogenated semiconductors.Research reported herein was supported by the Department of Energy, Division of Solar Technology, under Contract No. EY-76-C-03-1286 and by RCA Laboratories, Princeton, NJ 08540.     

Radiative recombination in ZnTe-CdSe and ZnSe-CdTe heterojunctions

Electroluminescence in II–VI heterojunctions has been investigated. Three types of ZnTe-CdSe heterojunctions were studied depending on the preparation method: Red diodes obtained by doping with O₂, yellow Cu-doped diodes and green undoped heterojunctions. Radiation was observed only in the forward biased junctions. At 80 K the external quantum efficiency is about 1.3% for red ZnTe-CdSe heterojunctions and decreases by one order of magnitude at room temperature. The radiation intensity for the other heterojunctions is the same at 80 K but at 150 K the luminescence disappears. The band diagram and the electroluminescence spectra show that the two-directional injection takes place in the ZnTe-CdSe heterojunctions. The blue electroluminescence for ZnSe-CdTe heterojunctions is due to the injection of hot holes in ZnSe from the high-resistivity layer at the interface and the recombination of these holes with the free electrons through an accepto level at 0.124 eV from the valence band. At 80 K slow periodic current oscillations accompanied by in-phase oscillations of the luminescence have been observed in ZnSe-CdTe heterojunctions.     

Radiative characteristics of high-frequency electrodeless helium lamps

Based on the system of equations describing the populations of highly excited helium atomic levels and the electron density and energy balance and on the Maxwell equations, we develop a model for an electrodeless high-frequency discharge in helium. We suggest a method of self-consistent calculation in a plasma-field system. The model developed is used to calculate the radiative characteristics of high-frequency electrodeless lamps. The derived dependences of line intensities on gas pressure, lamp radius, and discharge power are in good agreement with the experimental data.     

Radiative recombination of donor-acceptor pairs in ZnTe

Lifetime of the first excited state of donor-acceptor pairs has been measured in ZnTe as a function of the donor-acceptor distance. The measured lifetime for the radiative recombinations of donor-acceptor pairs agrees well with the calculated one in which the central cell correction for the 1s state of the acceptors is taken into account. It has been found that the lifetime depends on the impurity concentration. The concentration dependence is discussed in connection with the non-exponential decay of the luminescence observed for more distant donor-acceptor pairs.     

Auq+(q=53-47)激光等离子体的辐射复合速率系数

辐射复合过程在超组态碰撞辐射（SCROLL）模型中真实模拟非局域热动力学平衡（non-LTE）高Z材料Au激光等离子体M带谱5f-3d跃迁中各种复杂离子的电离态特性是一个主要过程。基于准相对论多组态Hartree-Fock理论和扭曲波近似,采用组态平均的方法,从头计算了金M带类铁金离子-类锗金离子的辐射复合速率系数,计算过程中包含了大量的单激发和双激发态,结果表明高Z元素由于自电离能级的广泛分布和复杂的级联效应,致使高Z元素的辐射复合系数不同于低Z元素的,其计算结果可用来模拟Au的激光等离子体M带5f-3d跃迁的平均电离度和电荷态分布及能级布居数。     

Auq+(q=53-47)激光等离子体的辐射复合速率系数

辐射复合过程在超组态碰撞辐射(SCROLL)模型中真实模拟非局域热动力学平衡(non-LTE)高Z材料Au激光等离子体M带谱5f-3d跃迁中各种复杂离子的电离态特性是一个主要过程.基于准相对论多组态Hartree-Fock理论和扭曲波近似,采用组态平均的方法,从头计算了金M带类铁金离子-类锗金离子的辐射复合速率系数,计算过程中包含了大量的单激发和双激发态,结果表明高Z元素由于自电离能级的广泛分布和复杂的级联效应,致使高Z元素的辐射复合系数不同于低Z元素的,其计算结果可用来模拟Au的激光等离子体M带5f-3d跃迁的平均电离度和电荷态分布及能级布居数.     

Radiative and nonradiative recombination times in semiconducting films

The radiation emitted spontaneously by a semiconductor which has been excited for a very short time decays exponentially with a time constant that depends on the recombination rate of electrons and holes. This recombination rate is the combination of radiative and nonradiative transition rates between conduction and valence bands of the semiconductor. The radiative recombination rate depends on the density of states of the electromagnetic field, which can be made to be dependent on the geometry. In this paper, we report on the dependence of the fluorescence lifetime upon the thickness of active thin films. For systems in which the radiative recombination rate is dominant over the nonradiative ones, the total recombination time can be changed by suitable modifications of the thickness of the film. In this situation, the nonradiative rate can be evaluated. We present experimental results for the case of cadmium sulphide (CdS) thin films.     

Radiative recombination from electron-hole drops in n-doped GaP

The observation of an isoelectronic impurity induced radiative no-phonon transition from electron-hole drops in strongly excited N-doped GaP is reported. The binding energy and carrier density within the drops are compared with theoretical values.     

Radiative recombination in iridium-doped silver bromide single crystals

The infrared emission spectrum of iridium-doped silver bromide results from a process that is competitive with the visible emission due to iodide centers in pure AgBr crystals. The emitting species is Ir³⁺, and experiments are described which help elucidate the nature of the radiative processes involved.     

Radiative recombination of holes in delta-p-doped gallium arsenide

Photoluminescence spectra of δ-p-doped GaAs structures of different doping levels are studied experimentally. It is found that set of PL bands observed in δ-p-doped samples recently is regularly broadened with doping concentration increase due to appearance of additional low-energy bands and their subsequent red shift at higher doping levels. A red shift of the bands and a change of their relative intensities were caused also by excitation laser intensity decrease and/or temperature increase. These results confirm our previous assumption that the bands are due to radiative recombination of spatially separated photoelectrons with holes occupying size-quantization levels of δ-layer potential well.     

Bi80+辐射复合过程的计算

基于Dirac-Slater自洽场方法,计算了Bi79+离子从低能到高能的光电离截面以及其逆过程Bi80+的辐射复合截面; 分析了Kramers公式的适用性;考察了多极效应、相对论效应在不同能区对辐射复合截面的影响;计算了Bi80+离子在电离阈值附近的辐射复合截面和辐射复合速率系数,考察了自由电子分布函数及电子的温度变化对速率系数的影响,并将计算结果同高精度的储存环合并束实验进行了对比.     

A visible helium plasma recombination laser

A small (active volume ≈ 6 cm³), fast Blümlein type, pulsed, transverse-discharge driven laser device exhibited afterglow lasing on the 3s³S-2p³P He transition at 706.5 nm in mixtures of helium and hydrogen or deuterium over a pressure range of 200 mbar. The main features of the laser pulses and relevant time-resolved fluorescence investigations are presented. Population inversion is attributed to the enhanced recombination pumping of upper level population and to hampered lower level population in the presence of H₂ (D₂).     

Radiative recombination of free excitons in GaAs quantum wells

We have measured the radiative lifetime of excitons in GaAs quantum wells under resonant excitation at 10 K using time resolved luminescence spectroscopy with 6 ps time resolution. The luminescence decay has two components: a fast one with a time constant τ₁ (∼ 17 - 40 ps) and a slow one with a time constant τ₂ (∼ 80 - 300 ps). τ₂ is the lifetime of thermalised excitens at 10 K. τ₁ is due to two mechanisms in parallel: the radiative recombination of excitons with k_u < K₀ and the scattering by acoustical phonens into non radiative exciton states (k_u > k₀ and J = 2). The variation with temperature of τ₁ gives the lifetime of the excitons at k = 0, τ₀, which varies between 20 and 50 ps depending on the sample.     

Radiative and relativistic effects in the decay of highly excited states in helium

A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 947 (1999)] measured a significant fluorescence yield of the He( 2lnl(')) photoexcited resonances, showing major qualitative differences from nonrelativistic predictions. We present a further theoretical study of these states, and perform R-matrix multichannel quantum defect theory calculations to extract fluorescence and ionization cross sections. These theoretical results are in excellent agreement with newer, higher-resolution measurements. Radiative and spin-orbit effects are quantified and shown to play an important role in the overall characterization of highly excited states.