+3价离子掺杂钨酸铅晶体发光性能和微观缺陷的研究

通过透射光谱、x射线激发发射光谱（XSL）的测试，研究了Bridgman法生长的几种不同+3价离子掺杂钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和x光电子能谱（XPS）的实验手段，对不同钨酸铅晶体的微观缺陷进行研究.实验表明，不同的+3价离子掺杂，对钨酸铅晶体发光性能的改善不同，并使得晶体中正电子俘获中心和低价氧的浓度发生不同变化.其中掺镧晶体的正电子俘获中心和低价氧浓度均上升，而掺钇和掺铋晶体的正电子俘获中心和低价氧浓度均下降，掺锑晶体则出现了正电子俘获中心浓度上升、低价氧浓度下降的情况.提 关键词： 钨酸铅晶体 +3价离子掺杂 正电子湮没寿命谱 x光电子能谱     

掺钇钨酸铅晶体发光性能和微观缺陷的研究

通过透射谱、X射线激发发射谱（XSL）的测试，研究了Bridgman法生长的掺钇钨酸铅晶体的发光性能，并利用正电子湮没寿命谱（PAT）和X光电子能谱（XPS）实验手段，对掺钇钨酸晶体的微观缺陷进行研究。实验表明，钇掺杂能够提高钨酸铅晶体的发光快成分比例，并使得晶体中的正电子俘获中心浓度下降，低价氧浓度下降。提出掺钇钨酸铅晶体中钇的掺杂主要以Y^3 占据VPb的形式存在。Y^3 占据VPb可能是钨酸铅晶体吸收边得到改善的原因，而由于晶体内低价氧浓度的减少，作为绿光发光中心的（WO3＋O^-)基团的减少可能会使发光快成分比例有所增加。     

Nb2O5掺杂对提高钨酸铅晶体发光性能的微观研究

通过透射谱、X射线激发发射谱(XSL)的测试，研究了布里奇曼(Bridgman)法生长的掺铌钨酸铅晶体的发光性能，并利用正电子湮没寿命谱(PAT)和X射线光电子能谱(XPS)的实验手段，对其微观缺陷进行了深入研究。结果表明，铌掺杂能够有效地改善钨酸铅晶体的350nm吸收带，提高钨酸铅晶体的发光快成分比例，并使得晶体中的正电子捕获中心浓度上升，低价氧浓度上升。提出掺铌钨酸铅晶体中Nb^5 将占据W^6 格位并使得晶体内部分(WO4)^2-根团成为(NbO3 Vo)^-，由此可改善钨酸铅的发光性能。     

掺镧PbWO4闪烁晶体的缺陷研究

利用正电子湮没寿命谱(PAT)和X射线电子能谱(XPS)研究了掺镧所引起的PbWO₄ 晶体缺陷的变化.结果表明：掺镧后,PbWO₄晶体中的正电子捕获中心铅空位(V< sub>Pb)浓度增加,并进一步诱导低价氧浓度的增加.讨论了掺La的作用机制,认为掺 La将抑制晶体中的氧空位,增加铅空位浓度. 关键词： 掺镧钨酸铅晶体 正电子湮没寿命谱 X射线电子能谱 缺陷     

Nd掺杂对Bi4Ti3O12铁电薄膜的微结构和铁电性能的影响

利用溶胶-凝胶法在Pt/Ti/SiO₂/Si(100)衬底上制备了Nd掺杂Bi₄Ti₃O₁₂(Bi_4-xNd_xTi₃O₁₂, x=0.00,0.30,0.45,0.75,0.85,1.00,1.50)铁电薄膜样品.研究了Nd掺杂对Bi₄Ti₃O₁₂薄膜的微结构和铁电性能的影响.研究结果表明:Nd掺杂未改变Bi₄Ti₃O₁₂薄膜的基本晶体结构.在掺杂量x<0.45时,Nd³⁺只取代类钙钛矿层中的A位Bi³⁺.当x=0.45时,样品剩余极化强度达最大值,在270kV·cm^-1的电场下为32.7μC·cm^-2.掺杂量进一步增加时,结构无序度开始明显增大,Nd³⁺开始进入(Bi₂O₂)²⁺层,削弱其绝缘层和空间电荷库的作用,导致材料剩余极化逐渐下降.当掺杂量x达到1.50时,掺杂离子最终破坏(Bi₂O₂)²⁺层的结构,材料发生铁电-顺电相变.     

掺铋BaF2晶体的制备及其近红外发光研究

通过温度梯度法制备了Bi₂O₃:BaF₂以及BiF₃:BaF₂晶体.在Bi₂O₃:BaF₂晶体中观察到了发光峰位于961 nm,半高宽202 nm的超宽带红外发光.在BiF₃:BaF₂晶体中检测到Bi²⁺和Bi³⁺可见区的发光,但是没有观察到红外发光.通过γ射线辐照实现了BiF₃:BaF₂晶体的近红外发光, 发光峰位于1135 nm,半高宽192 nm.讨论了Bi₂O₃和BiF₃掺杂BaF₂晶体的红外发光的机理.     

掺Bi离子锗铌酸盐红外发光玻璃的研究

用高温熔融法制备了Bi₂O₃掺杂的(0.9-x) GeO₂-xNb₂O₅-0.1BaO (含量x为摩尔分数, x=0, 0.04, 0.07, 0.1)系列玻璃. 测定了玻璃样品的差热分析(DTA)曲线、吸收光谱、发射光谱及X射线光电子能谱(XPS). 从DTA曲线分析得到玻璃的结晶起始温度与软化温度之差(T_x-T_g)达200℃以上. 吸收光谱中可观察到位于500, 700, 808和1000 nm处的吸收峰, 并随着Nb₂O₅含量x的增加吸收边带发生红移. 在波长为808 nm激光激发下, 观察到发光中心位于1300 nm处、荧光光谱半高宽约为200 nm的宽带发光. 荧光强度随Bi₂O₃掺杂量δ的增加先增强后减弱, 当掺杂量δ达到约0.01时, 荧光强度达到最强. 随着Nb₂O₅含量x从0.04增加到0.1时, 荧光强度逐步减弱. 样品的XPS峰分别位于159.6和164.7 eV, 它们介于Bi³⁺与Bi⁵⁺的特征结合能之间, 因此Bi³⁺与Bi⁵⁺可能同时存在于玻璃基质中. 从XPS及Bi离子的发光特性推断, 宽带的荧光发射可能起因于Bi⁵⁺. 随着Nb₂O₅含量x的增加, 荧光强度逐步减弱. 分析认为, Nb₂O₅取代GeO₂后形成了NbGe缺陷, 需要低价Bi离子进行电子补偿, 因而抑制了Bi⁵⁺形成, 致使荧光强度减弱.     

PbWO4闪烁晶体的辐照损伤机理研究

完成了640—1040℃温度范围内钨酸铅［PbWO₄(PWO)］晶体的退火实验,观察到较低温退火时晶体中本征色心吸收带(350nm)先是增加,其后随退火温度的升高而逐渐降低直至消除的全过程．分析了PWO晶体的本征缺陷和电荷补偿机制．讨论了退火过程中氧进入晶体后色心的产生和转化规律,并提出可能发生Pb³⁺→Pb⁴⁺的进一步氧化过程,从而导致Pb³⁺空穴中心的湮没．测量并比较了不同退火温度处理后PWO晶体的紫外辐照诱导色心     

掺镧PbWO4闪烁晶体的缺陷研究

利用正电子湮没寿命谱(PAT)和X射线电子能谱(XPS)研究了掺镧所引起的PbWO4晶体缺陷的变化.结果表明:掺镧后,PbWO4晶体中的正电子捕获中心铅空位(VPb)浓度增加,并进一步诱导低价氧浓度的增加.讨论了掺La的作用机制,认为掺La将抑制晶体中的氧空位,增加铅空位浓度.     

Bi2WO6光催化剂的γ射线辐射效应

本文首次研究了高能辐射(γ射线)对Bi₂WO₆纳米晶体结构和光催化性能的影响. 结果表明,尽管高能辐射不会改变Bi₂WO₆纳米晶体的形貌,但是Bi₂WO₆粉末的颜色在高吸收剂量辐照(507 kGy)后发生了明显的变化,并且辐照后Bi₂WO₆的XRD谱图也显示,随着吸收剂量的增加,(113)晶面对应的2θ从28.37°移到28.45°,说明晶格参数在γ射线辐照下还是发生了细微的变化. XPS表征结果证明,Bi₂WO₆晶体结构的变化源于高剂量辐射下氧空位缺陷的产生. Bi₂WO₆纳米晶体的禁带宽度(E_g)随吸收剂量的增加也出现减小的趋势. 用水溶液中亚甲基蓝的可见光照分解反应作为模型反应考察了辐照后的Bi₂WO₆纳米晶体的光催化活性,结果表明,辐照后的Bi₂WO₆纳米晶体的光催化活性随着吸收剂量的增加而逐渐升高. 将经过反应后的Bi₂WO₆纳米晶体再次回收,进行循环催化,发现这些辐照后的Bi₂WO₆纳米晶体在三次循环使用后光催化性能仍然能够保持,说明高能辐射产生的氧空位缺陷具有良好的稳定性.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.