铜铁镁三掺铌酸锂晶体的第一性原理研究

利用基于密度泛函理论的第一性原理,研究了Cu:Fe:Mg:LiNbO3晶体及对比组的电子结构和光学特性.研究显示,单掺铜或铁铌酸锂晶体的杂质能级分别由Cu 3d轨道或Fe 3d轨道贡献,禁带宽度分别为3.45和3.42 eV;铜、铁共掺铌酸锂晶体杂质能级由Cu和Fe的3d轨道共同贡献,禁带宽度为3.24 eV,吸收峰分别在3.01,2.53和1.36 eV处;Cu:Fe:Mg:LiNbO3晶体中Mg^2+浓度低于阈值或高于阈值(阈值约为6.0 mol%)的禁带宽度分别为2.89 eV或3.30 eV,吸收峰分别位于2.45 eV,1.89 eV或2.89 eV,2.59 eV,2.24 eV.Mg^2+浓度高于阈值,会使吸收边较低于阈值情况红移;并使得部分Fe^3+占Nb位,引起晶体场改变,从而改变吸收峰位置和强度.双光存储应用中可选取2.9 eV作为擦除光,2.5 eV作为读取和写入光,选取Mg^2+浓度达到阈值的三掺晶体在增加动态范围和灵敏度等参量以及优化再现图像的质量等方面更具优势.     

LiNbO_3:In:Fe:Cu晶体中的双波长非易失存储

为了提高晶体的非易失存储性能,采用双波长存储技术实验研究了LiNbO3:In:Fe:Cu晶体中的非易失存储,折射率调制度为1.04×10-4,记录灵敏度达到0.965 cm/J.与传统的双色非易失记录相比,该方法大幅度地提高了光栅的强度和记录的灵敏度.利用Kukhtarev带输运模型对双波长非易失记录过程中光栅的动态演化过程进行了数值模拟,同时讨论了氧化还原程度对双波长非易失全息记录的影响.理论与实验符合的较好.     

The radiothermoluminescence of (ZnS:CdS:Ag:Ni:Co) phosphors irradiated with beta-rays

The radiothermoluminescence characteristics have been studied for a number of (ZnS:CdS::Ag:Ni:Co) phosphors, with various cobalt impurity contents, after exposure to⁹⁰Sr beta-rays at room temperature. Thermoluminescent spectra show a peak wavelength of 7000 Å, which remains unchanged with increase in cobalt concentration. Thermoluminescence curves exhibit a single well-defined peak appearing at temperatures far above room temperature. This peak shifts to lower temperatures with increasing cobalt content. The relation between thermoluminescence response and dose is linear over the dose range of 1 to 500 rads. Thermoluminescence measurements made after storing the irradiated phosphor for 48 hours in dark have revealed an information loss of 4% over this storage period. The radiothermoluminescence characteristics, storage capacity and storage stability of these sulphide phosphors compete reasonably with those of lithium fluoride over the dose range of 1 rad to 500 rads.     

Sensitization in CaS:Bi:Tm phosphors

The emission spectra of calcium sulphide phosphors activated with bismuth, thulium, and both together are studied in the spectral range of 4000 Å to 8000 Å. The results indicate resonance transfer of excitation energy from Bi to Tm. Sensitizer to sensitizer transfer also appears to be appreciable. A plausible energy level diagram is proposed to explain the sensitization mechanism.     

钛宝石泵浦的Yb:YAG晶体的激光性能

测量了Yb:YAG晶体的光谱特性,用Ar⁺离子泵浦钛宝石激光器作为泵浦源泵浦Yb:YAG晶体,采用平平腔设计,当输出耦合镜T_1.053μm=4.26%,泵浦功率为1410mW时,得到320mW1.053μm的高效CW激光输出,斜率效率为54%,外推阈值功率为203mW。     

Acoustic cavitation series: part one: Acoustic cavitation: an introduction

Acoustic cavitation has been an active area of research for at least 30 years and interest in the subject shows no sign of diminishing. Cavitation may occur whenever high intensity ultrasound is applied to liquids, for example in such important applications as sonar, industrial processing and bio-medical research. Future issues will carry a series of articles reviewing the physics and technology of acoustic cavitation, each contributed by a well-known specialist. The present introductory article is a preface to the series, covering background history, explaining the scope of the subject and defining terms in common use. Also included is a list of the major sources of reference presently available, in the form of books, reviews and collections of papers.     

变色的ZnS：Mn/SrS：Ce/ZnS：Mn薄膜电致发光的研究

利用ZnS:Mn/SrS:Ce/ZnS:Mn多层结构,得到了一种可变颜色的薄膜电致发光器件。研究了这一器件的发射光谱随电压和频率的变化,并讨论了随电压的增加,发射光谱中蓝带和黄带的不同增长的原因,以及在不同电压下,发射光谱中蓝带和黄带随频率变化的不同趋势的原因。观察到随驱动频率的增加,发射光谱出现黄-蓝色位移。     

Microwave cavity perturbation technique: Part III: Applications

The resonant cavity perturbation method as described in the preceding two parts of this series is applied to study the electrodynamical properties of different materials in the microwave and millimeter wave spectral range. We briefly discuss the relevant uncertainties which are asociated with the different measurement techniques and we find that employing the amplitude technique it is possible to measure both the width and frequency to nearly the same precision. We then demonstrate the broad range of applicability of this technique by showing results obtained on several different materials, ranging from an insulator to a superconductor. The performance limitations of this technique are discussed in detail.     

a-C:N:H纳米尖端荧光产生的机理

用CH4,H2和NH3为反应气体,利用等离子体增强热丝化学气相沉积在沉积有碳膜的Si衬底上制备了a-C:N:H纳米尖端,并用扫描电子显微镜和微区Raman光谱仪对碳膜和纳米尖端进行了表征。结果表明:Raman谱中含有与碳和氮相关的峰,且纳米尖端的Raman谱比碳膜的Raman谱有很强的荧光背景。Raman谱中的峰说明沉积的碳膜和纳米尖端是a-C:N:H薄膜和a-C:N:H尖端。a-C:N:H纳米尖端的Raman谱中强荧光背景的产生表明其在激发光源照射的过程中发射了强荧光,对a-C:N:H纳米尖端产生强荧光的机理进行了探讨。     

HgSe:Fe quantum dots: growth and characterization

Mercury selenide and its ternary and quaternary modifications in the form Hg(A,B)Se with A, B magnetic ions, provide an interesting semiconductor family featuring different kinds of correlation effects. These effects manifest themselves already in three-dimensional, quasi-two-dimensional, and quasi-one-dimensional structures. We have succeeded now in fabricating HgSe:Fe quantum dots using three different growing procedures based on molecular beam epitaxy: (a) Stranski–Krastanov growth; (b) thermally activated surface reorganization; (c) pit filling. The special feature of the HgSe:Fe dots is the intrinsic population of the dot states by electrons, where a large amount of about 50–500 electrons form a many-electron system within a single dot. The formation of the dots was controlled in situ by RHEED. The morphology of the resulting structures was characterized by AFM. Subsequently, the electronic properties of the dots were investigated by megagauss magneto spectroscopy, indicating the presence of strong correlation effects as manifested in a 50% increase of the cyclotron mass in respect to that of structures with a higher dimensionality.     

Yb:YAG and Nd:YAG edge-pumped slab lasers

Experimental demonstrations of two edge-pumped zigzag slab lasers are presented. The Nd:YAG slab laser generated 127 W of multimode output power with 300W of pump power. Preliminary results with a Yb:YAG slab produced 46 W of output power with 315W of pump power. The edge-pumped slab design permits symmetric conduction cooling and efficient pump absorption and accepts large-numerical-aperture pump sources.     

RETRACTED ARTICLE: Polymer electrolytes: characteristics and peculiarities

Polymer electrolytes are an important component of many electrochemical devices. This paper reviews state-of-the-art of the electrochemical and physical properties of polymer electrolytes. This review mainly encompasses the properties of different salts, solvents, and polymer hosts, which are encaged in liquid electrolytes. The additions of filler in polymer electrolytes result in composite polymer electrolytes, having high mechanical integrity and ionic conductivity, that are ideal electrolyte for these applications. The next generation state-of-the-art room-temperature ionic liquids based electrolytes, which are far superior to corresponding nonionic solvent-based electrolytes, are also discussed. An erratum to this article can be found at     

Ceramic MgO:LiF: promising material for selective detector

The optical absorption and EPR spectra of transparent ceramic MgO:LiF samples irradiated in various reactors have been studied. The obtained results give evidence of the possibility of using the mentioned samples for selective estimation of the fast neutron dose by the methods of optical and radio spectroscopy.     

Photoluminescence processes in LaOCl:Bi and YOCl:Bi

The luminescence of rare earth oxychlorides LnOCL:Bi (with Ln = La and Y) is studied in detail. The main excitation bands, responsible for the blue and UV fluorescences, are attributed to the bismuth activator substituting for Ln³⁺ in the rare earth tetragonal site. The weak shoulder of these bands and the complex decay times are assumed due to a parasitical phase, La₂O₃ or Y₂O₃ doped by bismuth, an X-ray analysis confirming their presence in the samples. Finally, the existence of these phases does not seem to have an important effect upon the interpretation of the luminescence processes of the main center, as shown by the configuration curve model.     

Growth and photorefractive properties of near-stoichiometric In:Fe:Cu:LiNbO3 crystals

The near-stoichiometric LiNbO₃ crystal co-doped with In₂O₃, Fe₂O₃, and CuO has been grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere for the first time. The OH⁻ absorption spectra were characterized to investigate the structure defects of the crystals. The appearance of the 3506 cm⁻¹ absorption peak manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were also measured by the two-wave coupling experiments. The results show that the near-stoichiometric In:Fe:Cu:LiNbO₃ crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient than those obtained in the congruent In:Fe:Cu:LiNbO₃ crystal under the same experimental conditions. The material of near-stoichiometric In:Fe:Cu:LiNbO₃ crystal is a promising candidate for blue photorefractive holographic recording.     

Conversion of nitrogen oxides in N2:O2:CO2 and N2:O2:CO2:NO2 mixtures subjected to a dc corona discharge

This paper concerns the influence of a direct current (dc) corona discharge on production and reduction of NO, NO₂ and N₂O in N₂:O₂:CO₂ and N₂:O₂:CO₂:NO₂ mixtures. The corona discharge was generated in a needle-to-plate reactor. The positively polarized electrode consisted of 7 needles. The grounded electrode was a stainless steel plate. The gas flow rate through the reactor was varied from 28 to 110 cm³/s. The time-averaged discharge current ranged from 0 to 6 mA. It was found that in the N₂:O₂:CO₂ mixture the corona discharge produced NO, NO₂ and N₂O. In the N₂:O₂:CO₂:NO₂ mixture the reduction of NO₂ was between 6–56%, depending on the concentration of O₂, gas flow rate and corona discharge current. The NO₂ reduction was accompanied by production of NO and N₂O. The results show that efficient reduction of nitrogen oxides by a corona discharge cannot be expected in the mixtures containing N₂ and O₂ if reducing additives are not employed.     

Laser characteristics of Cr:Nd:GdCOB self-frequency-doubling crystal

The phase matching angle of GdCOB crystal is calculated. By using Xenon flash lamp as pump source, we have realized the free run from 1.06 μm to 0.53 μm in self-frequency-doubling Cr:Nd:GdCOB (bi-doped) crystal and Nd:GdCOB (uni-doped) crystal. The experimental results show that the threshold energies for bi-doped crystal and uni-doped crystal are 0.92 J and 1.00 J, respectively; when the pump energy is 10 J, the output energies of green laser for two kinds of crystals are 2.46 mJ and 1.96 mJ, respectively. The output energy of Cr:Nd:GdCOB crystal has an increase of 25% in comparison to that of Nd:Gd:COB crystal. In addition, we discuss ways to improve efficiency.     

Thermally stimulated luminescence of CaS : Bi : Pd phosphors

CaS phosphors co-activated with Bi⁺³ and Pd⁺² impurities in varying concentrations have been prepared and their thermoluminescence has been systematically studied. The general features of the curves are discussed and the activation energies have been estimated in three different ways. The escape frequency factor is determined using the theoretical model of Randall and Wilkins. Conclusions are drawn regarding the type of kinetics involved in the thermoluminescence process.     

Personal View: Synchrotron Radiation Instrumentation: A Personal Experience

The scope of this two-day meeting (held June 25–26, 2007), organized by the French MELUSYN (Medicine and Synchrotron Light) work group at the new synchrotron radiation facility SOLEIL (Saint-Aubin, France), was to create a timely forum for multi-disciplinary discussions on modern radiation biology. The meeting brought together physicists of diluted and condensed matter, chemists, biochemists, biologists, as well as physicians having a common interest in using synchrotron radiation in the UV, VUV, soft and hard X-ray ranges and the related techniques in order to explore at molecular, cellular or tissular levels various aspects of radiation effects on living systems and the medical consequences for radiotherapy.     

Structure and optical damage resistance of Zn:Mn:Fe:LiNbO3 crystals

The new non-volatile holographic storage materials, Zn:Mn:Fe:LiNbO₃ crystals, were prepared by Czochralski technique. Their microstructure was measured and analyzed by infrared (IR) transmission spectra. The optical damage resistance of Zn:Mn:Fe:LiNbO₃ crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of ZnO is over a threshold concentration. Its value in Zn(7.0 mol%):Mn:Fe:LiNbO₃ crystal is about three orders of magnitude higher that in Mn:Fe:LiNbO₃ crystal. The photoinduced birefringence change was measured by the Sénarmont's method. It decreased with ZnO concentration increasing. The dependence of the defects on the optical damage resistance was discussed.