Photo- and cathodoluminescence investigation of ZnO films

Photo- and cathodoluminescence spectra of ZnO films obtained by magnetron sputtering and annealed at different temperatures have been studied. The effect of irradiation in a scanning electron microscope on the cathodoluminescence spectra of these films is investigated. It is shown that even relatively small irradiation durations result in a noticeable change in signal intensity. Both signal enhancement and reduction can occur depending on the annealing temperature. Data obtained are explained by defect formation and rearrangement stimulated by electron irradiation.     

A self-consistent method for the determination of neutral density from X-ray impurity spectra

A new method for the determination of neutral densities and the electron lifetime from X-ray line spectra through charge exchange processes is proposed. The non-equilibrium population of neutrals and the charge exchange from their excited states in plasma regimes of high density and temperature have been calculated in a self-consistent manner through the introduction of an “effective diffusion rate”.     

Temperature dependence of the cathodoluminescence spectra of irradiated light-emitting-diode structures with multiple InGaN/GaN quantum wells

The cathodoluminescence spectra of regions of light-emitting structures with multiple InGaN/GaN quantum wells unirradiated and irradiated with an electron beam are investigated in the temperature range from liquid-nitrogen temperature to room temperature. It is shown that a new emission line with an energy of 2.69 eV emerges as a result of irradiation in addition to the initial 2.6 eV line. The intensity of the emission line associated with Mg in p-GaN also increases after irradiation.     

Conductivity-dependent cathodoluminescence in BaTiO3, SrTiO3 and TiO2

It is reported that similar cathodoluminescence spectra are excited by an electron beam striking BaTiO₃, SrTiO₃ and TiO₂ ceramics at room temperature. The energy location of the luminescence bands does not depend on various doping or reduction treatments. The luminescence intensity increases with the electron beam current as well as with the conduction electron density. The luminescence is interpreted as a fundamental transition of local character in the TiO₆ octahedron; the conduction electrons localized at the Ti sites in polaron states recombine with the 0–2p valence electron defects. The shape and energy location of the luminescence spectra are qualitatively in accordance with an explanation in terms of a configuration coordinate model.     

Growth,structure, and cathodoluminescence of Dy-doped ZnO nanowires

Dy-doped ZnO nanowires have been prepared using high-temperature and high-pressure pulsed-laser deposition. The morphology, structure, and composition of the as-prepared nanostructures are characterized by field emission scanning electron microscopy, X-ray diffraction, Raman scattering spectrometry, X-ray photoelectron spectrometry, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The alloying droplets are located at the top of the as-prepared Dy-doped ZnO nanowires, which means that the growth of the Dy-doped ZnO nanowires is a typical vapor-liquid-solid process. The luminescence properties of Dy-doped ZnO nanowires are characterized by cathodoluminescence spectra and photoluminescence spectra at low temperature (8 K). Two peaks at 481 and 583 nm, respectively, are identified to be from the doped Dy³⁺ ions in the CL spectra of Dy-doped ZnO nanowires.     

Transient optical absorption induced by an electron pulse in KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> crystals

The efficiency of formation and time evolution of radiation-induced structural defects and pulsed luminescence in KPb₂Cl₅ crystals under the action of a single electron pulse (E = 250 keV, τ = 20 ns) have been investigated. The spectra (1.1–3.8 eV) and relaxation kinetics (time interval 5 × 10^?8?5 s) of transient optical absorption and the pulsed cathodoluminescence spectra and decay kinetics (1.4–3.1 eV) have been measured in the temperature range 80–300 K. It is revealed that the induced optical density and its time evolution depend strongly on temperature, and the absorption relaxation time contains several components and reaches several seconds at T = 300 K. The decay kinetics of transient absorption and pulsed cathodoluminescence kinetics have different orders and are controlled by different relaxation processes.     

Low-voltage cathodoluminescence of ZnS single crystals

Bright blue and green cathodoluminescence from low resistivity ZnS crystals has been observed under the excitation of low-energy electron beams of several tens of volts; i.e., 40 fL at 50 V. Properties of the surface of the crystals are studied by the dependence of current and brightness on applied voltage and by the spectra of cathodoluminescence and photoluminescence.     

Comparison of luminescence spectra of natural spodumene under KrCl laser and e-beam excitation

Spectral characteristics of pulsed photoluminescence (PL) and pulsed cathodoluminescence (PCL) of a natural spodumene were investigated. PL was excited by laser radiation at 222 nm with pulse duration of 10 ns at FWHM. PCL was excited by electron beams with pulse duration from 0.1 up to 4 ns and with current densities of 40-200 A/cm². There was a dominant broad band at 600 nm due to the manganese impurity in PCL spectra. But in PL spectra, the orange band had the intensity comparable with intensities of intrinsic defect bands. At sample cooling by liquid nitrogen, the intensity of orange band in the PCL spectrum increased by two times and the short-wave shoulder of the band reduced.     

Raman-in-SEM,a multimodal and multiscale analytical tool: Performance for materials and expertise

The availability of Raman spectroscopy in a powerful analytical scanning electron microscope (SEM) allows morphological, elemental, chemical, physical and electronic analysis without moving the sample between instruments. This paper documents the metrological performance of the SEMSCA commercial Raman interface operated in a low vacuum SEM. It provides multiscale and multimodal analyses as Raman/EDS, Raman/cathodoluminescence or Raman/STEM (STEM: scanning transmission electron microscopy) as well as Raman spectroscopy on nanomaterials. Since Raman spectroscopy in a SEM can be influenced by several SEM-related phenomena, this paper firstly presents a comparison of this new tool with a conventional micro-Raman spectrometer. Then, some possible artefacts are documented, which are due to the impact of electron beam-induced contamination or cathodoluminescence contribution to the Raman spectra, especially with geological samples. These effects are easily overcome by changing or adapting the Raman spectrometer and the SEM settings and methodology. The deletion of the adverse effect of cathodoluminescence is solved by using a SEM beam shutter during Raman acquisition. In contrast, this interface provides the ability to record the cathodoluminescence (CL) spectrum of a phase. In a second part, this study highlights the interest and efficiency of the coupling in characterizing micrometric phases at the same point. This multimodal approach is illustrated with various issues encountered in geosciences.     

Luminescence investigations of cubic boron nitride doped with beryllium

The cathodoluminescence and photoluminescence spectra of cubic boron nitride doped with beryllium under high-pressure and high-temperature conditions are investigated. It is revealed that, upon doping of cubic boron nitride with beryllium, the cathodoluminescence spectra exhibit a broad stable band. An increase in the impurity content leads to a shift in the position of the maximum of this band toward the short-wavelength range from ～315 to ～250 nm and to a change in the crystal color from dark yellow to blue. The structure, the intensity, and the position of the band at the maximum are studied as a function of the temperature of the cathodoluminescence measurement. The nature of the band is tentatively interpreted in the framework of the model of recombination at defects of the donor and acceptor types. It is assumed that several overlapping subbands which are associated with differently charged acceptor levels of beryllium are located in the vicinity of the valence band in the electronic structure of the doped cubic boron nitride. It is found that the photoluminescence spectra of single crystals of the doped cubic boron nitride contain three previously unknown zero-phonon lines at energies of 2.135, 2.270, and 2.600 eV.     

Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC

Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors.     

Characterization of radiative centers in wide-band-gap materials by local cathodoluminescence by the example of europium-doped YAG

Europium-doped yttrium-aluminum garnet (YAG) samples were studied by local cathodoluminescence. The europium valence in YAG is 3+; an addition of a small amount of zirconium partially converted europium to the divalent state (2+). The local cathodoluminescence method made it possible to detect the presence of both europium valence states. Concentration dependences of the cathodoluminescence intensity and decay time for various spectral lines and bands were studied. The dependence of the cathodoluminescence intensity on the electron beam current density was studied. The results obtained were interpreted within the two-level model of the radiative center. The local cathodoluminescence method potential and the two-level model applicability were demonstrated. An analysis of the spectra allowed for the detection and identification of an unintentional impurity in one of the samples.     

Thermodynamic variables of microquasars inferred from tachyonic spectral maps

Tachyonic spectral densities of ultra-relativistic electron populations are fitted to the γ-ray spectra of two microquasars, LS 5039 and LSI +61°303. The superluminal spectral maps are obtained from BATSE, COMPTEL, EGRET, HESS, and MAGIC data sets. The spectral averaging is done with exponentially cut power-law densities. Estimates of the electron distributions generating the tachyon flux are obtained from the spectral fits, such as power-law indices, electron temperature and source counts. The internal energy and heat capacities of the source populations are calculated. An extensive entropy functional is defined for Boltzmann power-law densities and its stability is checked. The high-temperature limit of the thermodynamic variables is determined by the power-law index of the electron plasma, which enters in the scaling exponents as well as the amplitudes.     

Chatham合成钻石紫外阴极发光谱

用自制的阴极发光分析仪在JCXA-733电子探针上分析两批美国Chatham公司合成钻石的微区紫外-可见阴极荧光,结果表明Chatham合成钻石具有峰波长为234,268 nm等的紫外阴极荧光谱。不同批次的Chatham钻石的紫外阴极荧光谱特征也有所不同。这些紫外阴极发光谱在天然钻石和人工处理后的天然钻石中都没有发现,可能是Chatham合成钻石的特征谱,因而可能具有一定鉴定价值。经进一步完善后,紫外阴极荧光谱技术有望成为鉴别天然和合成钻石、不同公司合成钻石或同一公司不同批次合成钻石的有效方法。     

Spodumene and garnet luminescence excited by subnanosecond electron beams

Pulsed cathodoluminescence of spodumene and yttrium-aluminum garnet crystals activated by Mn²⁺ and Nd³⁺ ions, respectively, is investigated. The luminescence was excited upon crystal irradiation by electron beams with current densities of 35 and 100 A/cm² and average electron energy of ∼ 50 keV for 0.1, 0.25, and 0.65 ns. It is demonstrated that the electron beam duration decreased to several tenth of a nanosecond does not lead to essential changes of the mechanisms of pulsed cathodoluminescence excitation and character of its spectrum, but in this case, the intensity of luminescence of the hole centers increases compared with the intracenter luminescence.     

Spin dynamics of Rashba-Dresselhaus two-dimensional electron systems with electron-electron interactions

Spin dynamics of Rashba-Dresselhaus two-dimensional electron systems is studied by taking account of electron-electron interactions under the D’yakonov-Perel’ mechanism. The diffusion equations for charge and spin densities are obtained through decoupling of the interactions using the auxiliary Bose field. We show that the electron-electron interaction has no effect on the infinite spin lifetime when the Rashba and Dresselhaus coupling constants satisfy the condition α = ±β. If the general condition α≠±β is satisfied, the spin lifetime is finite and enhanced by the electron-electron interaction with the increment of the temperature in the ballistic regime. The increasing amplitude of the spin lifetime depends on the ratio of the temperature to the Fermi temperature.     

Superluminal cascade spectra of TeV γ-ray sources

Astrophysical radiation sources are scrutinized in search of superluminal γ-rays. The tachyonic spectral densities generated by ultra-relativistic electrons in uniform motion are fitted to the high-energy spectra of Galactic supernova remnants, such as RX J0852.0−4622 and the pulsar wind nebulae in G0.9+0.1 and MSH 15-52. The superluminal spectral maps of the unidentified TeV γ-ray sources HESS J1303−631, TeV J2032+4130 and HESS J1825−137 are inferred from EGRET, HEGRA and HESS data. Tachyonic cascade spectra are quite capable of generating the spectral curvature seen in double-logarithmic plots, as well as the extended spectral plateaus defined by EGRET flux points in the GeV band. The curvature of the TeV spectra is intrinsic, caused by the Boltzmann factor in the source densities. The spectral averaging with thermal and exponentially cut power-law electron densities can be done in closed form, and systematic high- and low-temperature expansions of the superluminal spectral densities are derived. Estimates on the electron/proton populations generating the tachyon flux are obtained from the spectral fits, such as power-law indices, temperature and source counts. The cutoff temperatures of the source densities suggest ultra-high-energy protons in MSH 15-52, HESS J1825−137 and TeV J2032+4130.     

驱动电压频率对固态阴极射线发光影响的研究

固态阴极射线发光(SSCL)是发光学中一种新的激发方式,引发出一些发光学中的重要问题,但是固态阴极射线发光的性质还不是十分清楚,需要进一步研究。文章用SiO₂作为电子加速层, 有机材料MEH-PPV为发光层, 在正弦交流电压驱动下实现了固态阴极射线发光,得到410和580 nm两个发光峰。通过研究这两个发光峰的性质,证实它们分别符合能带理论和分子理论。改变驱动电压的频率时,长波峰的发光强度随频率的增加而增加,而短波峰的发光强度随频率的增加而减小,这是由于这两个发光峰对应的上能级寿命不同引起的。     

Cherenkov Radiation in the Visible and Ultraviolet Spectral Ranges from 6-MeV Electrons Passing through a Quartz Plate

JETP Letters - Cherenkov radiation and pulsed cathodoluminescence spectra in the ultraviolet, visible, and near infrared regions generated by a 6-MeV electron beam passing through GE-014 and KU1...     

One-dimensional band-edge absorption in a doped quantum wire

Low-temperature photoluminescence-excitation spectra are studied in an n-type modulation-doped T-shaped single quantum wire with a gate to tune electron densities. With a nondegenerate one-dimensional (1D) electron gas, the band-edge absorption exhibits a sharp peak structure induced by the 1D density of states. When the dense 1D electron gas is degenerate at a low temperature, we observe a Fermi-edge absorption onset without many-body modifications.