The VUV‐VIS Spectroscopic Properties of Dy3+ Ion in Phosphors M5‐2XDyXNaX(PO4)3F (M=Ca,Sr, Ba) and Their Potential Applications in Mercury‐Free Lamps

The phosphors, fluorapatites M₅(PO₄)₃F (M=Ca, Sr, Ba) activated with Dy³⁺ ions, were prepared by a high‐temperature solid‐state reaction technique. The VUV‐UV excitation spectra and emission spectra under VUV/UV excitation were measured. The phosphors show broad and strong absorption near 172 nm and intensive emission with the chromaticity coordinates entering the white light region. Hence, the phosphors may be considered as suitable candidates for Hg‐free lamps.     

A Particle‐in‐Cell Simulation of the Breakdown Mechanism in Microdischarges with an Improved Secondary Emission Model

In this paper, the failure of the breakdown voltage from the Paschen's law at extremely small electrode separations is studied. The electrical breakdown in microgaps occurs at the voltages far below the Paschen curve minimum breakdown limit and the modified Paschen curve should be used. Offered explanation for the departure from the Paschen's law at small gap spacings is based on the increasing of the yield of the secondary electrons. The high electric fields existing in small gaps may enhance the secondary electron yield and this would lead to a lowering of the breakdown voltage and to the departure from the Paschen's law. Particlein‐cell/Monte‐Carlo (PIC/MCC) simulations with a new secondary emission model have been performed to estimate the importance of this mechanism in the discharge breakdown. Obtained simulation results suggest that deviations from the Paschen curve across the micron and submicorn gap spacing can be attributed to the ion‐enhanced field emissions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

One- and two-barrier excilamps on xenon dimers operating in the VUV range

Spontaneous emission sources in the VUV range based on one- and two-barrier pulsed-periodic gas (Xe) discharges are experimentally investigated. Volt-coulomb figures, as well as typical waveforms of current pulses and discharge voltage are presented. The time dependences of the voltage drop across the gas-discharge plasma, excitation power, and excitation energy are calculated. The radiation power versus xenon pressure, exciting pulse repetition rate, and average excitation power is determined. The radiation power average densities for one- and two-barrier excilamps are found to be 20–30 and ～40 mW/cm², respectively.     

Stimulated emission of inert gas mixtures in the VUV range

Amplification properties of continuous VUV emission of cooled discharge in mixtures of heavy inert gases are studied experimentally. The discharge current is 10–50 mA, the pressure is 100 GPa. Results pointing to amplification near the resonance line of xenon λ=146.96 nm are obtained. The amplification coefficient is measured to be κ=0.1 cm^?1. The problem of radiation outcoupling from the active medium remains to be solved for practical implementation of a VUV laser.     

Numerical simulation of a barrier discharge in Xe

Components of plasma of a barrier discharge in xenon are calculated for various values of the parameter E/N. Features of excimer population are analyzed. Efficiencies of the VUV emission yield are calculated, and basic channels of energy loss determining the efficiency are established.     

Luminescence spectra of solid xenon excited by volume discharge

The luminescence spectra of solid xenon excited by a volume discharge are studied for the first time. The majority of the energy is emitted in the VUV spectral region due to the radiative decay of excitons. A specific feature of the spectra in the UV and visible regions is the complete absence of lines belonging to neutral excited particles (one-center Xe* and two-center Xe ₂ ^* excitons) and to diatomic Xe ₂ ⁺ ions. Numerous lines of the Xe⁺ ion are shifted by 0.1–0.3 nm with respect to their positions in the gas; the larger the shift, the stronger the distortion of the line shape. Based on the data obtained, a mechanism by which solid xenon is excited and ionized by fast drifting electrons is proposed.     

One-dimensional single and multipulse simulations of the ON/OFFvoltages and the bistable margin for He, Xe, and He/Xe filled plasmadisplay pixels

A one-dimensional plasma model developed for AC plasma display pixels is used to perform multipulse and single-pulse simulations to model the maximum sustain voltages, the minimum sustain voltages, and the voltage margins for 100% helium, 100% xenon, and for 2% xenon in helium and a 400 torr pressure (p) and a gap (L) of 100 μm. The multipulse simulations describe the growth in wall voltage at the so-called ON voltage and the decay in wall voltage at the so-called OFF voltage. For square wave forms, the ON voltage is the voltage at which a pixel attains to a stable operation in which a discharge occurs in each succeeding pulse and the wall voltage equal to the applied voltage. The OFF voltage is the voltage at which a pixel that is ON goes off and no further discharges occur. Experimental data for helium show the hysteresis in the discharge current observed when the voltage is increased to turn ON pixels and then reduced to turn OFF-pixels in a panel. Simulations which match the helium data are also shown. The difference between the ON and OFF voltages defines the bistable margin. For the helium-xenon Penning mixture, the ON and OFF voltages determined by multipulse simulations are almost identical to the values obtained from the wall voltage transfer curve method. In the helium-xenon Penning mixture, the ionization rate for xenon ground state increases dramatically compared to its ionization rate in pure xenon due to the modification in the electron velocity distribution function in the mixture. This feature provides enhanced volumetric ionization in the discharge and hence a rapid growth rate of the wall voltage which is desirable for a sharp transition from OFF to ON in a pixel     

VUV spectrum of the barrier discharge in a krypton-xenon mixture

VUV spectra of a barrier discharge in a krypton-xenon mixture at the pressure P=400 hPa were experimentally studied. The xenon addition was varied in a range of 0.01–1%. The supply voltage frequency was 20 kHz. The form of spectra and their evolution at different xenon impurity concentrations were analyzed by solving the system of nonlinear differential equations simulating the main processes taking place in the active phase of a discharge and in the afterglow. The analysis supports the results obtained earlier and qualitatively describes the experimental spectra.     

Development of Ionization waves in an Atmospheric‐Pressure Micro‐Plasma Jet

Present study investigated the development of ionization waves in an atmospheric‐pressure plasma jet. Plasma was ignited by 6 kHz sinusoidal voltage applied to a cylindrical electrode surrounding the 500 μm inner diameter quartz tube and positioned 10 mm upstream from the tube orifice. The plasma current was observed using a plane electrode placed 20 mm downstream from the tube orifice. The spatial development of ionization waves was monitored by registering the optical emission along the axis of the tube. At voltages in range of 5.5 ‐ 7.5 kV only one pulse occurred during positive half‐period while at higher voltages the number of pulses increased up to 6 ‐ 7 per half‐period. The development of the first and subsequent pulses during one half‐period was essentially different. For the first pulse the sharp rise of optical emission characterizing the front of the ionization wave occurred initially near the high‐voltage electrode and moved towards the tube orifice and further in the He jet. The propagation of ionization wave coincided with the rise of the displacement current measured at the plane electrode. For subsequent ionization waves of the same half‐period, the emission occurred initially at the tube orifice and the ionization wave developed simultaneously in two directions: towards the high‐voltage electrode and towards the end of the jet. The velocity of ionization wave inside the tube was in range of (2. 5 ‐ 5.0) · 10⁴ m/s for first wave and as high as 1.2 · 10⁵ m/s for subsequent waves. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ultrahot electron formation under excess electron drift through solid Xe

The formation of "hot" (8 eV) electrons under excess electron drift in a moderate electrostatic field through solid xenon has been experimentally proved by observation of secondary electrons emitted from the photocathode. At T=77 K and U=1000 V one drifting electron produces about 20 (172 nm) photons, the efficiency of electric field-to-vacuum ultraviolet emission conversion is 15% tending to grow with temperature. A self-sustained electric discharge has been generated in solid Xe using a three-electrode cell with a zinc cathode.     

Optical characteristics of the steady-state plasma of a longitudinal discharge in a He/CFC-12 mixture

The emission from the plasma of a contracted longitudinal dc discharge in a He/CF₂Cl₂ mixture in the wavelength range 130–300 nm is investigated. It is shown that the discharge plasma emits within the range 150–260 nm. The emission consists mainly of the broad bands of Cl₂ molecules and single-charged chlorine ions. The pressure and composition of the working mixtures, the discharge current, and the time during which the emitter can operate on a single gas fill are optimized to attain the best characteristics of UV and VUV radiation. The results obtained are of interest for developing a steady-state source of VUV and UV radiation to be applied in microelectronics, photochemistry, and medicine.     

低气压氙气介质阻挡放电的一维仿真研究

通过建立一个自洽耦合的一维流体模型来描述低气压氙气介质阻挡放电(DBD),并采用有限元法对模型进行数值仿真研究,得到了不同外加电压幅值和频率下的气体间隙压降、放电电流、介质表面电荷随时间的变化关系以及电子、离子、中性粒子和空间电场的时域分布.仿真结果表明:介质表面电荷对放电的点燃与熄灭起着关键的作用;在一个放电周期内,根据气体间隙压降的变化情况,介质表面电荷可按六个阶段进行分析;随着外施电压幅值的增加,间隙击穿逐渐提前至外施电压过零点之前发生,放电更为剧烈;随着外施电压频率的提高,气体间隙压降减小,间隙容易击穿,放电也更加均匀.粒子及空间电场的时域分布表明氙气DBD为典型的辉光放电.     

An influence of the electrode emission properties and the gas temperature on the discharge ignition voltage in the mixture of argon with mercury vapor

Kinetics of electrons, ions and metastable excited atoms in the interelectrode gap of a low-current discharge in the argon-mercury mixture is simulated, and the discharge ignition voltage as a function of the temperature and the cathode ion-electron secondary emission rate is calculated. The mixture temperature dependence of the minimum value of the ion-electron secondary emission rate ensuring a given discharge ignition voltage is found.     

Van der Waals molecules and collision pairs of noble-gas atoms ahead of a shock wave front

The effect of creation of an excess concentration of free electrons in an anomalously thick layer (≈5 cm) ahead of an explosively driven shock wave in noble gases is discussed and interpreted. This effect is the ionization of excited 1_u-state molecules produced due to the absorption of a small intensity flux (as compared to the ionization one) of photons (with energies substantially lower than the atom ionization threshold) by unexcited colliding complexes and van der Waals molecules. A model is proposed which explains the excitation of xenon molecules ahead of the radiationless shock wave of an open discharge. The absorption spectra of colliding complexes and van der Waals molecules adjacent to each other near the atomic absorption lines can be resolved into two spectra, and these spectra can be changed by an increase in gas temperature. As a result, radiation capable of exciting van der Waals molecules penetrates through the shock wave of an open discharge and excites xenon molecules there. The present work develops further the knowledge concerning the radiation energy transport in the shock wave front. It also proves that in front of an explosively driven shock wave a great number of excited molecules of noble gases are actually formed, and this means considerable progress toward a VUV laser with optical pumping. Translated from Preprint No. 56 of the P. N. Lebedev Physical Institute, Moscow, 1993.     

Interference effects in the UV(VUV)‐excited luminescence spectroscopy of thin dielectric films

The problem of exciting UV and VUV light interference affecting experimental photoluminescence excitation spectra is analysed for the case of thin transparent films containing arbitrarily distributed emission centres. A numerical technique and supplied software aimed at modelling the phenomenon and correcting the distorted spectra are proposed. Successful restoration results of the experimental synchrotron data for ion‐implanted silica films show that the suggested method has high potential.     

On the Role of Capacitance Determination Accuracy for the Electrical Characterization of Pulsed Driven Dielectric Barrier Discharges

A dielectric barrier discharge (DBD) of coaxial geometry has been investigated. The discharge cell was filled by 100 mbar of argon and driven by positive square voltage pulses with a rise time of 20 ns and 75 ns. The internal discharge characteristics such as the discharge current, the gas gap voltage, the instantaneous power and energy have been determined from measured current and voltage waveforms. The peculiarities of the experimental evaluation of the discharge parameters are discussed in detail. Special attention is paid to the accurate experimental determination of the key capacitance values of the DBD, namely the capacitance of the reactor cell C_cell and the capacitance of the dielectric barriers C_d. The influence of the capacitance value accuracy on precision of electrical characterization is demonstrated and it is shown that a small uncertainty in the C_d value leads to large errors in the evaluation of the gas gap voltage. Nevertheless, the obtained accuracy of the capacitance values allows the reliable comparison of the electrical DBD parameters. These are sensitive to the mode of discharge excitation. The shortening of the voltage rise time leads to the increase of the total and instantaneous energy as well as the peak power dissipated into the discharge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

脉冲氙灯放电过程分析与实验测定

脉冲氙灯是一种新型光源,利用量子理论以及气体放电理论分析了脉冲氙灯放电过程,设计了放电测试系统,实验测定了放电过程中的电压、电流和光脉冲信号。结果表明：在预电离阶段自由电子浓度较低,能量较低;气体放电阶段灯内形成电子崩,使得自由电子浓度的增大,放电电流迅速上升,电压下降;离子复合时释放出光子形成光脉冲,氙灯脉冲的光能量输出和光谱特性与复合电子能量、氙气复合能级相关,而当输入能量与氙灯的能耗不一致的时候,将导致充电电容反复充放电,而使电路产生振荡。对于分析脉冲氙灯放电过程,优化放电回路参数设计和脉冲氙灯的生产具有重要意义。     

Proton and electron impact on molecular and atomic oxygen: I. High resolution fluorescence spectra in the visible and VUV spectral range and emission cross-sections for dissociative ionisation and excitation of

Molecular oxygen O₂ was dissociated in collisions with protons and electrons in the intermediate velocity range (p⁺-energies: 17-800 keV, e^--energies: 0.2-2 keV). Fluorescence from excited atomic and singly ionised fragments and from singly ionised molecules was detected in the VUV and in the visible and near UV spectral range. Highly resolved spectra are presented for the VUV (46-131 nm) and the near UV/visible (340-605 nm) spectral range. Absolute emission cross-sections have been determined for dissociative ionisation and excitation leading to fluorescence in the VUV. Results are compared with published data. Received 9 September 1999 and Received in final form 15 December 1999     

Discharge initiation in a hollow-cathode plasma source of electrons

Experimental results on discharge initiation in a hollow-cathode plasma source of electrons are reported. The discharge is initiated by ions flowing out from the accelerating gap into the discharge region. The ions are generated by a high-voltage glowing discharge occurring in the accelerating gap at a pressure of more than 2 Pa and a voltage of no less than 2 kV. It is shown that an increase in the ion-electron emission coefficient, which can be raised by properly choosing the gas-metal pair, decreases the threshold ion current initiating the discharge at a fixed discharge voltage.     

Excitation of UV radiation by a pulsed-periodic discharge in xenon

Optoelectrical characteristics of a pulsed-periodic discharge in xenon are investigated experimentally under conditions such that the product of the electrode gap length and the gas pressure is in the range of 4–20 Torr cm. High conversion efficiency of the energy deposited into vacuum UV radiation in a discharge sustained by 0.1-gms voltage pulses at a repetition rate of 1–10 kHz is demonstrated. It is shown that this effect is related to the fast expansion of the negative glow occurring after each discharge ignition. The conditions are determined under which the discharge is not accompanied by the heating and sputtering of the cathode.