+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.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.