Electroluminescence in ZnO-ZnSe systems

A study was made of electroluminescence in ZnO-ZnSe: Cu, Cl type luminophors as a function of band-gap of the resultant host lattice. By altering relative proportions of the oxide and the selenide, a number of samples were prepared, giving electroluminescent emission covering a wide spectral range from green to red. The emission spectrum shifts toward the red due to successive reduction of band gap of the combined system as the percentage amount of ZnSe is increased. The effect of firing atmosphere in the preparation of these luminophors is also described. Taking (0.5 ZnO, 0.5 ZnSe): Cu, Cl as a specific sample, different emission bands were recorded when excited by A.C. field and the ultraviolett radiations. The electroluminescent brightness of the sample follows the relationB=B ₀ e^?b/√¯v at normal frequencies and voltages.     

Field dependence of a.c. Electroluminescence in ZnS: Mn,Cu, Cl film panels

Electroluminescent (EL) film panels of ZnS: Mn, Cu, Cl operated by a.c. electric field are studied at room temperature. The emission spectrum consists of a single peak at 590 nm. The EL emittance B varies with frequency f of the applied a.c. electric field as B = B_s ? B_m exp ? f/f_c where B_s, B_m and f_c are constants. This equation indicates that B approaches a saturation value B_s when f?f_c and a linear relation between B and f when f?f_c. At a fixed frequency f, B is found to depend on the applied voltage V as B = A exp [-G/F + V^{$\text{1}\text{2}$})] where A, G and F are constants. This formula is valid at all stages of the operating life of the film panel.     

AC electroluminescence of ZnS: Cu,Cl, Mn thin films in the structure In2O3(Sn)-ZnS: Cu,Cl, Mn-SiOx-Al

AC electroluminescence of ZnS: Cu, Cl, Mn thin films in the structure In₂O₃(Sn) - ZnS: Cu, Cl, Mn-SiO_x Al was studied. Vacuum-evaporated films 0.5 to 2.0 μm thick, excited with sinusoidal voltage of 80–200 V and up to 2 kHz gave the luminance response fulfilling Alfrey-Taylor's relation. Thus the electroluminescence model, suggested by these authors for a ZnS monocrystal, can be applied also for ZnS thin films.     

ZnS…Cu电致发光电压传感器及其温度漂移补偿

利用ZnS…Cu电致发光粉末与环氧树脂胶混合,设计制作了一种梯形电极结构的电压传感单元,实现了电致发光电压传感器输出信号的温度漂移补偿。电致发光电压传感信号通过2根塑料光纤传输到2个硅光电探测器,并选择其开路电压作为传感器的输出信号。在同一外加电压条件下,梯形电极区域内的电场分布是不均匀的,因而不同场点的发光亮度不同。通过测量梯形电极区域内2个不同发光点的发光强度随外加电压的变化,并对两路输出电压传感信号进行数据拟合与计算,可获知被测电压的有效值,并可实现对输出信号温度漂移的补偿。在-40~60℃范围内,采用上述温度漂移补偿方法测量了有效值在0.7~1.5 k V范围内的工频电压,传感器输出信号的非线性误差低于1.6%,验证了该温度漂移补偿方法的有效性。     

The influence of the activator concentration on electroluminescence properties of thin layers in a system ZnS: Cu,Mn, Cl

The influence of activators, especially copper, on the electric properties of vacuum-evaporated electroluminescent layers excited by dc voltage is investigated. In the course of the “one step” method of preparation, non-uniform incorporation of the activators occurs. The layers are divided into three groups according to the copper concentration. 1 — “low” (1×10^?3 g Cu/g ZnS) with the emission stimulated at Al^? electrode, 2 — “medium” (5–8×10^?3 g Cu/g ZnS) with the emission at both polarities, 3 — “high” (9×10^?3?5×10^?2 g Cu/g ZnS) with the emission at Al⁺ electrode. Layers in these groups differ not only in their electrical properties and in the existence of the forming process but they have also various distribution of the light-emitting regions. The light emission has been found in the intermediate regions between the microcrystalline grains as well as on the interface between the microcrystalline grain and ZnS phosphor phase. According to structural properties the light emission originates from microcrystalline grains too.     

A simple procedure for electroluminescent phosphor assessment

A simple assessment procedure is described which facilitates optimal selection of an electroluminescent phosphor based on the measurement of two optically deduced energies—absorption and emission. These two energies are used as input for an appraisal analysis based on a classical configuration-coordinate diagram model of the phosphor. A phosphor performance figure-of-merit is proposed as a consequence of the formulation of this assessment procedure. This procedure is then used to rationalize the relative performance of five electroluminescent phosphors (ZnS:Mn, BaAl₂S₄:Eu, SrS:Ce, SrGa₂S₄:Ce, CaGa₂S₄:Ce). Additionally, two cathodoluminescent phosphors (ZnS:Ag and ZnS:Cu) are appraised using this methodology, suggesting that this procedure may be of some utility in the evaluation of other types of phosphors.     

Effect of an electric field on the I–V curves of DyBa2Cu3−x Oy/1 wt % Pt HTSC ceramics

This paper reports on an experimental study of the effect of a magnetic field, B≤70 G, and an electric field, E=120 MV/m, on the critical current I _c and I–V curves of DyBa₂Cu_3?x O_y HTSC ceramics (x=0 and 0.2), both undoped and doped with 1 wt % Pt. It has been established that, in stoichiometric ceramics (x=0) at 77 K, I _c drops sharply (by more than an order of magnitude) already at very low B<1 G. In copper-deficient ceramics (x=0.2), I _c decreases with increasing B slowly, with Pt-doped samples exhibiting [on the dropping I _c (B) dependence] a peak effect, i.e., an increase rather than decrease of I _c at B≈10 G. As for the effect of an electric field on I _c and the I–V curves (the E effect), it is not observed in ceramics of a stoichiometric composition. DyBa₂Cu_2.8O _y samples acted upon by an electric field reveal a substantial increase in I _c and a decrease in the resistance R for I>I _c . In the case of DyBa₂Cu_2.8O_y/Pt, the electric field practically does not affect I _c but R decreases for I>I _c . In a sample placed in a magnetic field, the magnitude of the E effect is observed to correlate with the I _c (B) dependence. In particular, in Pt-doped samples, the E effect decreases with increasing magnetic field B not gradually but with a maximum appearing at B ≈10 G, i.e., in the region of the peak effect in the I _c (B) dependence. The data obtained suggest the conclusion that the electric-field effect in ceramics exhibiting weak links of the superconductor-insulator-superconductor (SIS) type correlates with magnetic vortex pinning.     

On the role of moisture in the ageing and restoration processes in ZnS: Cu electroluminophores

An investigation is carried out on the simultaneous effect of wet atmosphere and exciting electric field on aged electroluminescent ZnS: Cu cells (ELC), due to which a better stability and an increase of brightness up to 30% were registered. A model is proposed for the ageing process in ELC in a dry atmosphere, based on the partial reduction of the second Cu_2?xS (0 ? x ? 1) phase, and a model is suggested for the brightness restoration of ELC in wet atmosphere also, based on the partial oxidation of Cu₂S.     

Decay of enhanced density and damping of plasma flows after the electrode biasing termination on the CASTOR tokamak

Electrode biasing is a standard tool for modification of both edge and global plasma parameters on the CASTOR tokamak (R=0.4 m,a=85 mm,B _T=1.3 T,I _p1≈9 kA,q _a≈10). During a steady state phase of a discharge, a polarization voltage is applied on an electrode immersed into the edge plasma. This voltage causes radial currents that create radial electric field and, due to theE×B drift, they cause an enhanced rotation. Then, as a consequence, the interaction with walls decreases and particle confinement and density increase. Recently, the decay of plasma density and plasma flows after the termination of the biasing period was investigated on the CASTOR tokamak. These observations are linked to processes and mechanisms that control generation of radial electric fields in plasmas and damping ofE×B sheared flows and that therefore represent a key issue for understanding the transition to improved confinements modes. In the contribution, measured time scales of the transition to the ohmic regime after the biasing termination will be shown. Further, possible consequences of these measured scales for the valuation and explanation of important processes in the plasma will be discussed.     

Kinetic theory of runaway breakdown in inhomogeneous thundercloud electric field

Kinetic theory of runaway breakdown in inhomogeneous thunderstorm electric field is developed. The kinetic equation, boundary and initial conditions are formulated. Spectrum of X-ray emission generated by runaway electrons is calculated. It has quite a specific form: a sharp maximum at energies 50–60 keV and a rapid fall both to the smaller and higher energies. The intensity of the emission is growing effectively with the relation E_m/E_c (of maximal electric field E_m to critical field E_c) and falling down sharply with the distance near the point z where electric field E(z) is equal to critical field E_c.     

以陶瓷厚膜为绝缘层的红色ZnS:Sm,Cl电致发光器件

报道采用高介电常数的陶瓷厚膜作绝缘层、ＺｎＳ：Ｓｍ,Ｃｌ作为发光层的红色薄膜电致发光器件。测量了器件的电致发光光谱和亮度电压曲线,研究了发光机理和效率电压等特性。制备的器件在电驱动下１６Ｖ启亮,最大亮度为１８．４ｃｄ／ｍ＾２,最大效率为０．０６１ｍ／Ｗ。     

Effect of chlorine concentration on the spectral characteristics of electroluminescence in ZnS: Cu: Cl phosphor

ZnS: Cu: Cl phosphor prepared under a vacuum firing process is found to give blue electroluminescence with emission peak at 460 nm which remains unaltered with the frequency of the excitation voltage. Addition of excess chlorine in the phosphor gives blue, green and red emission at 460, 520 and 640 nm. The intensity of the blue band decreases and it finally disappears as chlorine concentration is increased. A scheme involving three energy levels attributed to Cu²⁺, Cu⁺ and Cl^- centres in ZnS explains the experimental results completely.     

Dynamics of magnetic insulation failure and self-organization of an electron flow in a magnetron diode

The dynamics of back cathode bombardment (BCB) instability in a magnetron diode (a coaxial diode in a magnetic field, B ≡ B _0z ≡ B ₀) is numerically simulated. The quasi-stationary regime of electron leakage across the high magnetic field (B ₀/B _cr > 1.1, where B _cr is the insulation critical field) is realized. An electron beam in the electrode gap is split into a series of bunches in the azimuthal direction and generates the electric field component E _θ(r, θ, t), which accelerates some of the electrons. Having gained an extra energy, these electrons bombard the cathode, causing secondary electron emission. The rest of the electrons lose kinetic energy and move toward the anode. Instability is sustained if the primary emission from the cathode is low and the secondary emission coefficient k _se=I _se/I _{e, BCB} is greater than unity. The results of numerical simulation are shown to agree well with experimental data. A physical model of back-bombardment instability is suggested. Collective oscillations of charged flows take place in the gap with crossed electric and magnetic fields (E × B field) when the electrons and E × B field exchange momentum and energy. The self-generation and self-organization of flows are due to secondary electron emission from the cathode.     

Polarized emission of doped ZnS crystals

Polarization of light emitted in various spectral ranges was studied in two single crystals ZnS:Cu, Cl and ZnS:Ag, Cu, Al. The G-Cu, B-Cu and a small amount of S-A centers have been identified in the ZnS:Cu, Cl crystal by the spectral and polarization methods. The B-Ag band was found in the spectrum of the ZnS:Ag, Cu, Al crystal and its polarization properties investigated. This emission appears to be always polarized perpendicular to the [111]_c axis of the stacking faults independently of the polarization of the exciting light. The symmetry of the B-Ag center is not lower than that of the host lattice. Analogy with G-Cu centers suggests a model for the B-Ag center in which the polarization comes from the symmetry properties of the Ag²⁺ orbitals in the trigonal field of stacking faults.     

Eine Lumineszenzkammer

It has been shown that an external electric field gives rise to a splitting of theR ₁ emission lines of ruby (77°K). The resulting changes on the laser output were investigated withDC andAC electric fields. The application of an electric field modifies the amplification per path in a predictable way. Maser action is delayed or even suppressed depending upon the pumping level. At large fields (E?130 KV/cm) the amplification is reduced by a factor of two; an excess inverted population of twice the field-free value is required to maintain maser action. The energy stored in this way can be released in an intense maser pulse when the electric field is switched off suddenly.     

Effect of excitation intensity and electric field on the photoconductivity relaxation in CdxHg1−x Te/GaAs polycrystalline layers

The photoconductivity relaxation and the stationary photoconductivity in the n-Cd_0.8Hg_0.2Te compensated polycrystalline layers at T=300 K have been investigated as a function of the light intensity and the strength of applied electric field E. It is demonstrated that, at low excitation intensities, the saturation of stationary photoconductivity and a decrease in the relaxation time with an increase in E are caused by the minority carrier extraction. The effect of minority carrier extraction is analyzed with due regard for the internal electric field of potential barriers in intergranular layers. It is assumed that the features of nonequilibrium-carrier recombination, which proceeds through several channels and depends on the excitation intensity and extraction electric field strength, can stem from the polycrystalline structure of the Cd_0.8Hg_0.2Te layers.     

Degradation of superconducting properties in MgB2 by Cu addition

The (MgB₂)_2−xCu_x (x=0-0.5) superconducting system was prepared by a solid-state reaction technique. Microstructural evolution and transport properties including resistivity versus temperature up to a magnetic field of 6 T, activation energy, thermoelectric power and Fermi energy, E_F, and the corresponding velocity, V_F, values of the samples prepared were also investigated. The XRD analysis showed a multiphase formation and no detectable solution of Cu in MgB₂. Two different impurity phases, MgCu₂ and CuB₂₄, have been identified and their peak intensity increased when the Cu concentration increased. The temperature dependence of the resistivity of the samples showed a metallic behavior down to T_c. But, for the Cu concentrations above 0.3 the superconducting phase transition completely disappeared. The magnetic field strongly affects the electrical properties. For x=0.0 samples, the transition is found to be sharp, ΔT∼1 K, but it becomes broader with increasing magnetic field and Cu concentration. The calculated values of carrier concentration, n, of the samples are showed a sharp decrease with increasing Cu content. For x=0.0 sample the n was calculated to be 12×10²¹ cm⁻³, but for the x=0.5 sample it decreased to 1.3×10²¹ cm⁻³. We found that the activation energy, U(B), decreased sharply with increasing magnetic field. According to thermoelectric power and Fermi energy, E_F, calculations the decrease of the carrier concentration by the additions of Cu into MgB₂ gives a decrease in E_F and this could be attributed to a shift of the Fermi level towards the top of the σ-hole band.     

Nonreciprocal light birefringence in the R 3B7O13 X Boracites (R=Co, Cu, Ni; X=I, Br)

The field and angular dependences of nonreciprocal birefringence (NB), which is linear in magnetic field B and is due to magnetic-field-induced spatial dispersion, have been studied in the cubic (symmetry class T _d) paraelectric phase of the R ₃B₇O₁₃ X boracites (R=Co, Cu, Ni; X=I, Br) at a wavelength λ=633 nm. It is shown that the NB in crystals with different 3d and halogen ions exhibits the same anisotropy. The relation between the A and g parameters, A=2g, which determine the NB anisotropy, suggests that the microscopic mechanism of the NB is the manifestation of second-order magnetoelectric susceptibility at optical frequencies.     

Parametric x-ray radiation from 500-MeV electrons in a tungsten single crystal with a surface mosaicity less than 1.5′

The yield of parametric x-ray radiation from a tungsten single crystal irradiated with a E=500 MeV electron beam from the Tomsk Sirius synchrotron was studied experimentally in Bragg geometry. The tungsten sample was 1.7 mm thick and had a surface mosaicity less than 1.5′; it was oriented in such a way that the (111) face was at the Bragg angle of θ _B=45° with respect to the electron-beam direction. The x-ray photons were detected at the angle of 2θ _B=90° with respect to the electron beam. The angular distributions of parametric x rays are compared with those calculatedwith allowance for actual experimental conditions.     

Scaling law for a low-pressure gas breakdown in a homogeneous DC electric field

Gas breakdown in nitrogen, air, and oxygen in a dc electric field at various interelectrode distances L is studied experimentally. A scaling law for a low-pressure gas breakdown U _dc =f(pL, L/R) is deduced. According to this scaling law, the breakdown voltage U _dc is a function not only of the product of the gas pressure p and the gap length L, but also of the ratio of the gap length L to the chamber radius R. It is shown that, for any dimensions of the cylindrical discharge chamber (in the range of L/R under investigation), the ratio of the breakdown electric field to the gas pressure p at the minimum of the ignition curve remains constant: (E _dc /p)_min≈const. A method for calculating the ignition curve in a cylindrical discharge chamber with arbitrary values of L and R is proposed.