A Probe Method for Determination of time Evolution of Metastable Atoms Density in a Flowing Afterglow Plasma

The Langmuir Probe Measurement of the electron density and electron temperature has been made in the argon flowing afterglow plasma. Furthermore the metastable and charged particle densities evolution in the afterglow plasma are investigated by means of a numerical solution of the set of balance equations. From the fitting of the results of these calculations to the experimental data obtained from Langmuir probe measurements it is possible to determine the evolution of the metastable atoms density in the flowing afterglow plasma.     

Methane Conversion in the Flowing Afterglow of a Dinitrogen Microwave Plasma: Initiation of the Reaction

The reaction of methane in the nitrogen afterglow is studied by combination of direct measurements and computer experiment. The experimental data were obtained by optical emission spectroscopy of the discharge, by gas chromatography of resulting stable products and by probe diagnostics of charged species in afterglow plasma. The simulation was based on a macroscopic kinetic approach covering 24 species and 61 reactions with input data given by the afterglow experiment. In the present stage of the modelling the initiation of methane conversion was studied. It was found that, contrary to active discharge, in the afterglow plasma the active neutral species (mainly excited dinitrogen molecules) are most important for the dissociation of methane into CH_x and H radicals.     

温度对长余辉发光玻璃发光性能的影响

在还原气氛下, 制备了稀土Eu₂O₃ , Dy₂O₃掺杂的铝硅酸盐长余辉发光玻璃。分析了不同温度对SrAl₂O₄ : Eu, Dy发光玻璃的余辉发光的影响,比较了SrAl₂O₄ : Eu和SrAl₂O₄ : Eu, Dy发光玻璃的余辉发光的时间积分强度。结果表明:SrAl₂O₄ : Eu, Dy长余辉发光玻璃的发射光谱存在455,515 nm两个发射峰值,并且其余辉衰减正比于t^-0.8。SrAl₂O₄ : Eu, Dy长余辉发光玻璃余辉发光时间积分强度在150 K附近开始增加,并在275 K达到最大;Dy³⁺离子是造成空穴陷阱的主要原因。     

Afterglow of manganese centres in pulse-excited ZnS:Mn

The afterglow of self-activated and manganese centres in ZnS-Mn by excitation with a pulsed nitrogen laser is investigated. Assuming that a time-independent part of the excited “blue” centres returns to the ground state under energy transfer to the “yellow” centres, an equation describing the decay kinetics is derived. The comparison with the experimental data shows satisfactory agreement in the time interval up to 120 μs. A maximum in the afterglow curve arises within this limit.     

Afterglow of GaN wurtzite-structure crystals doped by rare-earth metals

The effect of impurity distribution and total defect concentration on the transport of nonequilibrium carriers has been estimated and specific features of afterglow in GaN and GaN〈Eu, Sm, Er〉 crystals revealed by measuring delayed near-edge photoluminescence spectra. A decrease in the total carrier concentration is shown to correlate with the afterglow in GaN wurtzite-structure crystals. The influence of additional illumination at a wavelength of 5145 Å on the evolution of delayed near-edge photoluminescence spectra was estimated in crystals with different Fermi level positions.     

Mn4+掺杂的新型铝酸盐红色长余辉材料

用高温固相法合成了红色长余辉发光材料LiAl₅O₈:Mn⁴⁺,Li₅AlO₄:Mn⁴⁺,LiAlO₂:Mn⁴⁺,发现前两种材料有红色余辉,这方面并没有报道过,并对这两种材料的发光性能作了研究,指明了不同基质中发光强弱不同原因。对不同Mn⁴⁺掺杂浓度的材料做了浓度依赖关系研究,确认Mn⁴⁺的发光是²E→⁴A₂的跃迁。Mn⁴⁺的发光是个宽带谱,材料在紫外区有强的吸收,发射谱范围可达620~770nm,峰值在675nm。对长余辉机制进行了探讨。     

Measurement of the electron distribution function in flowing afterglow plasma by means of Langmuir probe

Conclusion In the present report an attempt has been made to use the second derivative method for measurements of the electron distribution function in flowing afterglow plasma. It has been shown that using the cross-correlation technique, this method seems to be a useful tool for flowing afterglow plasma investigation.     

Afterglow工作模式下ECR离子源脉冲束的产生

为满足国家大科学工程兰州重离子冷却储存环的要求,在14.5GHz ECR 离子源上进行afterglow工作模式的实验,首次产生了高电荷态脉冲束流Ar¹¹⁺和Ar¹²⁺,给出了初步实验结果,并对结果进行了分析和解释.     

Helium Afterglow without Metastable Particles

Optics and Spectroscopy - We study the afterglow of a pulsed barrier discharge in helium with a small admixture of neon (10‒2%), which creates a plasma with a low density of metastable...     

白色长余辉材料CaxMgSi2O5+x：Dy3+系列的发光性能

制备并研究了一系列具有白色长余辉的钙镁硅酸盐材料,Ca_xMgSi₂O_5+x:Dy³⁺(x=1,2,3)。在紫外激发的发射谱中观察到来自Dy³⁺的4f组态内发射:对应⁴F_9/2→⁶H_15/2跃迁的蓝色发射(480nm)以及对应⁴F_9/2→⁶H_13/2跃迁的黄色发射(575nm)。低压汞灯(254nm)辐照后产生的长余辉光谱成分与发射谱相同,蓝光与黄光的混合组成白色光。对所研究的大部分样品,白色长余辉发射持续时间超过1h。研究了发射光强度对Dy³⁺浓度的依赖以及黄光与蓝光强度比与Dy³⁺掺杂浓度之间的关系,发现不同的基质有不同Dy³⁺浓度的依赖关系。室温以上的热释光谱表明所研究材料在室温以上具有丰富的热释光峰,因此有潜力进一步改善其长余辉性能。结合实验结果和以往研究,简要讨论了这一类材料的陷阱来源和长余辉发射机理。     

Comprehension of Jet Physics from the Analysis of the Gamma-Ray Burst Afterglow Parameter Distributions

The discovery of a short gamma-ray burst (GRB), GRB170817A, in association with a gravitational wave (GW) and a bright kilonova started a new era in the high-energy astrophysics. The observation of GRB170817A and more recently, GRB200826A and GRB211211A, a short and a long burst, respectively, with a possible kilonova, reinforce the concern about new ways of classification. For this reason, a new machine learning technique is applied to Swift-BAT data, searching for morphological similarities in the light curves. The resulting map is characterized by two distinct groups, although still correlated with standard T90 duration. Since a jet viewed off-axis could explain the emission from GRB170817A, the modeling of this kind of sources is of great importance. A public code called JetFit, based on the “boosted fireball” model, is applied to fit Swift-XRT afterglow light curves of short and long GRBs, with known red-shift, from 2005 to 2021. JetFit does not model the flaring activity. For this purpose, a new technique to remove the time flaring phases, is developed. This analysis provides a comprehensive study of the prompt and of the afterglow phase, trough the study of the best-fit parameters.     

A contribution to the study of the influence of metastables in the flowing afterglow plasma

The paper describes an experimental apparatus based on the flowing afterglow technique which enables the study of the role of metastable atoms of the carrier gas by means of titration of the reactant vapour of gas into the flow tube. A study of the behaviour of the electron and ion density and electron distribution of Ar* metastables (Ar as the carrier gas) using Penning ionization of the ethyl alcohol (CH₃CH₂OH) (titration vapour) has been made by means of a described experimental set-up. The method of estimation of the metastables concentration in the decaying flowing afterglow plasma by Langmuir probe technique with use of titrant technique is also studied.     

Eine Modellvorstellung für das „Auroral Afterglow“ und das „Pink Afterglow“

Based on own measurements of the decay of light intensity and electron density, a simple model for the auroral afterglow and the pink afterglow is proposed. To a certain extent the model can account for the influence of pressure and tube diameter on the behaviour of the afterglow. The first decay of the electron density towards the first minimum seems not to be influenced by creation processes for electrons during 3 to 15 ms. Therefore, the first decay can be used to measure the neutralization processes of electrons and positive ions. At pressures lower than 3 torr the electrons are removed by ambipolar diffusion with a rate given byD _a ·p≈2100 torr·cm²·s^?1. From this value an electron temperature of about 7200 °K could be derived. Assuming that ambipolar diffusion will remain the dominant loss process the time dependence of the electron creation rate has been evaluated. At a pressure of 1,75 torr the maximum electron creation rate was 4·10¹² s^?1·cm^?3. At the same time the emission density rate of the first negative bands was found to be 2.7·10¹³ cm^?3 s^?1. During one decay process about five times more electrons are created than the initial number. To explain the proportionality found between the electron density and the emission of the first negative bands, it is assumed that the ions, presumable N ₂ ⁺ -ions, are repeatedly excited to theB ² Σ _u ⁺ -state by metastables.     

Afterglow and thermoluminescence of ZrO2 nanopowders

A careful study of the phosphorescence afterglow and the thermoluminescence (TL) of sol-gel-prepared m-ZrO₂ nanocrystalline powders in an extended temperature range ?100 to 300 °C was carried out. Wavelength-resolved TL proved the existence of a single active luminescence centre in this temperature range. A TL method based on various heating rates was used to derive more reliable trap depths of 0.75, 0.95, 1.25, 1.46 and 1.66 eV whereas deconvolution methods provided somewhat lower values. The most intense room-temperature afterglows (that were easily observable beyond 1000 s) were obtained from samples annealed at 1250 and 1500 °C, and were attributed mainly to depopulation of the 1.25 eV traps.     

长余辉材料SrAl2O4 ∶ Eu,Dy中Eu的 价态变化及对发光性能的影响

采用高温固相法,先在空气气氛下制备了SrAl₂O₄ ∶ Eu,Dy,后对其进行还原→氧化→还原处理。X射线衍射结果表明,经过还原→氧化→还原处理后样品的晶体结构没有改变。样品的发射光谱测试表明,在高温空气气氛下有少量的Eu³⁺还原成Eu²⁺。Eu³⁺和Eu²⁺有不同的发光特性,Eu³⁺产生的是线状特征光谱,发射峰值在592,616 nm。Eu²⁺产生的是带状光谱,带的中心位置在513 nm。经过还原处理的样品和经过氧化处理的样品相比,Eu²⁺的浓度得到显著提高,而Eu³⁺的浓度则急剧下降。对Eu²⁺的氧化、Eu³⁺的还原的机理进行了细致地讨论。另外,样品的热释光谱测试表明,经过氧化气氛处理和经过还原气氛处理过的样品的热释光峰值有很大的变化,但陷阱能级深度基本不变,在0.65 eV左右。这表明,对长余辉材料SrAl₂O₄ ∶ Eu,Dy进行还原→氧化→还原处理,Eu离子价态和发光强度会产生变化,并不影响其中Dy离子的陷阱能级。     

Eu,Dy共掺杂SrAl2O4长余辉材料制备新工艺

活化Al-Sr合金粉末水解制备SrAl₂O₄长余辉材料的前驱体,并采用高温固相反应法制备出Eu,Dy共掺杂的SrAl₂O₄长余辉材料,对其微观结构和发光特性进行了研究。实验结果表明:前驱体中Al、Sr元素在微观状态下分布均匀,所制成的长余辉发光材料的发射主峰位于520nm附近,为典型的Eu²⁺离子4f5d-4f的特征发射,初始亮度达到18cd/m²,余辉时间长达46h。     

A Tunneling Model for Afterglow Suppression in CsI:Tl,Sm Scintillation Materials

Combined radioluminescence, afterglow and thermoluminescence experiments on single-crystal samples of co-doped CsI:Tl,Sm suggest that samarium electron traps scavenge electrons from thallium traps and that electrons subsequently released by samarium recombine non-radiatively with trapped holes, thus suppressing afterglow. Experiments on single crystals support the inference that electrons tunnel freely between samarium ions and are trapped preferentially as substitutional Sm⁺ near V_KA(Tl⁺) centers where non-radiative recombination is the rate-limiting step. Afterglow in microcolumnar films of CsI:Tl,Sm is enhanced by inhomogeneities which impede tunneling between samarium ions, but is partly suppressed by annealing.     

Pressing to the extremes

In the last decade the study of ion-neutral reactions has been dramatically advanced by the development and energetic exploitation of the steady-state flowing afterglow method by Eldon Ferguson and his colleagues at the National Oceanic and Atmospheric Administration (NOAA), Boulder, Colorado. This new technique has provided a very large number of ion–molecule rate coefficients for reactions at thermal energy.

In this method a fast flow of carrier gas (usually helium) is established in a long flow tube, the reactant ions (A⁺) are generated near the gas input end of the tube (the excitation region) and these ions are carried along the tube in the carrier gas flow. The neutral reactant (B) is introduced into the flowing gas stream near the mid-point of the flow tube so that the reaction A⁺+ B →products, takes place along the remainder of the tube length (the reaction region). The reactant ion A⁺ and any ions produced in the reaction are monitored by a mass spectrometer located at the gas exit end of the tube. The variation of the A⁺ mass spectrometer signal as a function of neutral reactant injection rate B yields the rate coefficient k for the reaction if gas flow rates and tube dimensions are known.

The great advantage and versatility of the steady-state flowing afterglow system lies primarily in the separate control that can be exercised over the ions and the neutrals prior to the reaction and also to the fact that the atomic processes occurring in the afterglow are susceptible to many diverse forms of investigation such as emission and absorption spectroscopy, laser spectroscopy, microwave interferometry and Langmuir probes, as well as mass spectrometry. Furthermore, chemically unstable neutral particles can be readily studied in these systems.     

Stability of Self-Gravitating Magnetized Hall Plasma with Electrical and Thermal Conductivity through Porous Medium

The problem of stability of a self-gravitating, infinite homogeneous gas in the presence of magnetic field is investigated. The medium is assumed electrically and thermally conducting. The effect of porosity, electrical conductivity, thermal conductivity and Hall current is investigated on the self-gravitating plasma flowing through porous medium. The relevant linearized equations of the problem are stated and dispersion relation is obtained. The effect of Hall current on the condition of the instability of the system is examined for both longitudinal and transverse mode of propagation and found that in longitudinal propagation Hall effect does not change the condition of instability but modifies the Alfvén wave mode. The stability of the system is discussed by applying Routh-Hurwitz criterion and it is found that Jeans criterion determines the stability of the system. Thermal conductivity and porosity have a destabilizing influence on the medium. The general condition for instability of the system is also derived.