Temperature-Dependent Defect-Induced New Emission in ZnSe Crystal

The temperature-dependent photoluminescence behaviour of chemical vapour transport （CVT）-grown ZnSe crystal is investigated. A new emission band appears when temperature is reduced to 155K. It is shown that the new emission band is strongly related to defect emission peaked at around 2.1 eV. The emergence of the new emission band is accompanied by decreasing emission intensity of free exciton, as well as redshiR of defect emission with temperature decreases. The activated energy of the defect state is estimated to be 60.6 meV, which is approximately equal to the energy difference between the new emission and the free exciton emission at 155K.     

Optical processes in the formation of stimulated emission from ZnO nanowires

This paper studies power dependent photoluminescence spectra, the stimulated emission occurring at ultraviolet (UV) band instead of the green emission band of ZnO nanowires, which are prepared with a chemical reduction method. The dynamics of the UV emission and green emission is given to demonstrate the reason of stimulated emission occurring at UV band but not the green emission band under high excitation, which indicates that the slow decay rate of trap state makes it easy to be fully filled and saturated, while the fast decay rate of near-band-edge exciton state makes the UV emission dominate the radiative recombination under high excitation. The UV emission, as well as the corresponding stimulated emission, occurs in competition with the green deep-trap emission. In addition, when pump fluence further increases, the multiple lasing modes appear. The dependence of these lasing modes on the pump fluence is first discussed. This diagram should be helpful to understand and design the optical nanodevices of ZnO nanowires.     

浅ZnCdSe/ZnSe量子阱的光泵受激发射

本文主要研究浅ZnCdSe/ZnSe单量子阱在77K温度下的光致发光。在不同激发密度下,讨论了该结构的发光机制,把77K温度下的受激发射归结为是激子-激子散射所引起的。文中还分析了在浅ZnCdSe/ZnSe量子阱中能够实现与激子相关的受激发射的原因。     

脉冲电场下两种电极材料表面电子发射阈值特性的实验研究

研究了金属表面电子发射阈值的测量原理.以待测材料为阴极,以法拉第筒作为阳极收集电子.在"晨光号"加速器上,测量了不同粗糙度的304L不锈钢和铝表面电子发射阈值及经表面涂覆工艺处理后这两种电极材料表面电子发射阈值.研究发现:电极表面磨光可以抑制电子发射,随着粗糙度的增加,电子发射阈值降低;金属表面涂覆对抑制电子发射效果更为显著,电子发射阈值增加了一倍.     

Luminescence of Bi3+-activated LaOBr,a system with emission from different states

The luminescence properties of LaOBr-Bi³⁺ are reported. Two luminescent centres are observed. These are ascribed to isolated Bi³⁺ ions and to a second BiOBr-rich phase. The emission of the isolated Bi³⁺ ion shows a remarkable temperature dependence. At low temperatures the emission is in the UV region. At higher temperatures the UV emission disappears and an emission in the visible region appears. At still higher temperatures the visible emission disappears and the UV emission reappears. The emission in the visible region is ascribed to a charge-transfer transition.     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性. 关键词： 场发射 纳米金刚石 尺度效应 热载流子     

PVK/BCP体系电致激基复合物的研究

在PVK/BCP双层电致发光器件中发现了电致激基复合物的发光,器件的光谱中,除了有与光致发光相同的发光峰,在长波方向还有一个新的发光峰,该发光峰就是电致激基复合物的发光,发光来源于BCP的激发态向PVK基态的跃迁。PVK∶BCP混合型器件由于复合区域扩展,BCP分子可以与PVK充分接触,因此电致激基复合物的发光更强。不论是在双层器件还是在混合型器件中,随驱动电压的增加,电致激基复合物的发光都会增强,而混合型器件更加明显,当电压比较高时,器件只有电致激基复合物的发光了,而没有本征发光。     

The luminescence of self-activated and copper-doped zinc selenide

The photoluminescence excitation and emission spectra of crystals of zinc selenide doped with copper or chlorine have been measured. The luminescence studies show that crystals doped with chlorine contain a slight trace of copper contaminant. Since the self-activated emission associated with chlorine and the low-energy copper emission overlap in the red region of the spectrum, it is necessary to remove all traces of copper from a crystal to isolate the self-activated emission. This has been done by heating crystals in molten zinc. In this way it has been possible to show that at 85 °K the self-activated emission band lies at 6150 Å, whereas the copper-red emission occurs at 6400 . The self-activated emission is excited strongly in a band centred at 4850 Å, while the copper-red emission is excited in a band centred at 5100 Å. The various transitions Å involved are discussed.     

Spontaneous emission coupling factors in planar micro-cavity lasers with distributed Bragg reflectors

In this article, a considerable value of spontaneous emission factor is estimated based on the spontaneous emission radiation patterns in micro-cavity lasers. After the spontaneous emission for a dipole in the micro-cavity is studied, the confinements of vacuum fields and electrons are considered together for a quantum well in the micro-cavity laser. The TE mode and TM mode spontaneous emission spectra are presented for a single quantum well embedded in a planar micro-cavity laser at 300 K. The results show that the TE mode spontaneous emission spectrum is enhanced, whereas the TM mode spontaneous emission is suppressed greatly. The maximum values obtained for the spontaneous emission coupling factors are 0.2 and 0.0055 for a dipole and a quantum well planar micro-cavity laser with distributed Bragg reflectors, respectively.     

Strong blue excitonic emission from CdS nanocrystallites prepared by LB technique

CdS nanocrystallites formed in ordered fatty acid LB multilayers exhibited strong surface states emission ∼550 nm and weak excitonic emission ∼400 nm. Treatment with aqueous CdCl₂ resulted in the suppression of surface states emission and enhancement of the blue excitonic emission. Subsequent annealing in air at 200°C caused an order of magnitude enhancement of excitonic emission. The growth of nanocrystallites during annealing as seen from the red-shift of excitonic absorption and emission is suppressed by the CdCl₂ treatment. The hindered growth of nanocrystallites, the significant enhancement of excitonic emission from CdS, and the suppression of surface states emission are attributed to surface passivation of CdS nanocrystallites by surface oxide formation.     

反铁电陶瓷的强电子发射特性研究

采用掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,研究了脉冲电压激励下陶瓷的电子发射特性.当激励电压为800V、抽取电压为0V时,得到1.27A/cm²的发射电流密度;当抽取电压增加到4kV时,获得1700A/cm²的发射电流密度.分析了发射电流随抽取电压的变化关系,讨论了反铁电陶瓷强电子发射的内在机理.结果表明：掺镧锆锡钛酸铅反铁电陶瓷能够在较低的激励电压(400V)下实现电子发射,发射电流远大于按照Child-Langmuir定律计算出的电流,三接点附近局域反铁电—铁电相变产生初始电子发射,初始电子电离中性粒子形成等离子体,增强了电子发射. 关键词： 铁电阴极 反铁电体 电子发射     

HDP-HSMM的磨削声发射砂轮钝化状态识别*

在高精度金属材料磨削加工中,刀具即砂轮的状态对加工效率和加工质量具有重要的影响。钝化程度较高的砂轮不适于加工精密工件,需提前预警并修整更换砂轮。该文提出一种通过磨削声发射信号来检测砂轮钝化状态的方法。首先,对于采集到的信号进行小波软阈值降噪。然后,将其分割成多个有重叠的帧,并提取每帧信号的8个特征组成声发射数据集。最后,通过分层Dirichlet过程-隐半马尔可夫模型来建立声发射数据集和不同的砂轮钝化状态之间的非线性关系,旨在识别砂轮钝化状态。结果表明,上述检测方法能有效识别砂轮的不同钝化状态并能对整个加工过程中的砂轮钝化程度进行自动划分,其在测试数据集上的准确率达到93.7%,可以为实际工业应用提供理论指导。     

电子俘获材料Eu,Sm∶CaS荧光特性的研究

研究了电子俘获材料Eu ,Sm∶CaS在室温下的荧光激发谱和荧光辐射谱。荧光激发谱由四个激发带构成 ,是由Eu2 + 的 4f7→ 4f55d跃迁和基质吸收所产生的。可见光激发下的荧光辐射谱是由一个极强的宽带和两个极弱的窄带构成 ,紫外光激发下的荧光辐射谱中不仅出现了以上三个辐射带 ,还出现了七个较强的窄带。这些荧光辐射带分别是由Eu2 + 的 4f65d → 4f7、Sm3 + 的 f→ f、Eu3 + 的 f→ f跃迁所产生的。研究还发现 ,当激剂浓度一定时 ,Eu2 + 的辐射带明显比Sm3 + 的辐射带强。     

Identification of the transition responsible for the visible emission in ZnO using quantum size effects

The emission properties of suspensions of nanocrystalline ZnO particles with different particle sizes were studied. Two emission bands were observed, one being an exciton emission and the other the visible emission of ZnO. The energy of both emissions depends on the particle dimensions due to size quantization. A linear relationship between the energetic maxima of the two emission bands is found. Because of the difference in effective masses of electrons and holes in ZnO, the slope of the linear relationship clearly indicates that the visible emission is due to the transition of an electron from the conduction band to a deep trap. The nature of the deep trap is also considered.     

人体体表超微弱生物发光与多种生理和病理状态关系的实验研究

一种非损伤性直接测定人体体表指端超微弱生物发光的装置,已被我们通过10年2000例的研究发展了起来。现将体表发光与多种生理和病理状态关系结果介绍如下。 1.从361例正常人各年龄组测定发现,体表发光计数率随年龄增加而升高,呈S型曲线,与人体生长规律吻合。显示光子数增加与衰老有关。 2.血清高血脂组病人体表发光率显示高于正常刘照组,P<0.02～0.05,指出体表发光与血脂浓度有关。 3.肿瘤病人的体表发光率显著低于非肿瘤对照组,P<0.1～0.001。 4.体表发光与吸烟密切相关:(1)吸烟导致早衰;(2)吸烟导致肺、胃肠、心血管系统的损害;(3)吸烟全过程动力学曲线观察提示,肿瘤人吸烟5分钟后,体表发光值达峰值,然后缓慢衰退,半衰期约30分钟。     

单晶LaB_6阴极材料典型晶面的电子结构和发射性能研究

单晶LaB_6是一种理想的热发射和场发射阴极材料,其不同晶面表现出不同的发射性能.采用基于密度泛函理论的第一性原理计算分析了LaB_6单晶的(100),(110),(111),(210),(211)和(310)典型晶面的差分电子密度、能带结构和态密度,并对光学区熔法制备的高质量单晶LaB_6的上述典型晶面的热发射性能进行了测试.理论计算结果表明LaB_6各晶面结构的不同和电子结构的差异导致LaB_6发射性能具有各向异性,晶面内La原子的密度越大、费米能级进入导带越深、费米能级附近态密度越大及其在导带区域的分布宽度越宽、导带在费米能级附近分布越多,晶面的逸出功越低,发射性能越好.热发射测试结果表明,当阴极测试温度为1773 K,测试电压为1 k V时,(100),(110),(111),(210),(211)和(310)晶面的最大发射电流密度分别为42.4,36.4,18.4,32.5,30.5和32.2 A/cm~2,其中(100)晶面具有最佳的发射性能.     

Intense directional lasing from a deformed square-shaped organic-inorganic hybrid glass microring cavity

Intense directional light emission from a deformed square-shaped organic light-emitting microring cavity was observed. The ring cavity was a dye-doped organic-inorganic hybrid glass film coated upon a square-shaped fiber. From the near-field and far-field emission patterns and their emission spectra we found, for the first time to our knowledge, the simultaneous existence of chaotic whispering-gallery modes and four-bounce reflection modes. The two types of mode have different emission directions, different lasing thresholds, and different spectral linewidths. High-contrast angle-modulated light emission was also observed. We could control modulation and angular spread of emission by controlling the deformation of the cavity.     

Field emission characteristic of screen-printed carbon nanotube cathode

The fabrication of carbon nanotube emitters with excellent emission properties is described. The multi-walled carbon nanotubes (MWNTs) produced by chemical vapor deposition (CVD) method were purified with oxidation method and mixed with organic binding pastes and then screen-printed on glass substrates with ITO film. We applied anode voltage gradually to refine the emission behavior of the emitter by cleaning the top surface of screen-printed carbon nanotubes (CNTs). The density of the carbon nanotubes is about 2.5×10⁸/cm². Diode field emission experiments were performed in dynamic vacuum system to study the emission current, the emission uniformity, etc. Bright and stable character emission images were obtained in the diode structure and the emission current could approach 1 mA/cm².     

纳米银粒子的发光特性研究

研究了不同粒径和表面修饰的纳米银粒子的发光特性。研究结果表明,在不同波长光激发下,纳米银粒子在362 nm附近出现较强的发射峰,592和725 nm附近出现较弱的发射峰。随着激发光波长增加,发射峰强度下降,362 nm附近的发射峰红移。纳米银颗粒对210 nm的激发光最为敏感。发射峰波长与纳米银粒子表面修饰状态和颗粒尺寸关系不大,只是随着颗粒尺寸的减小,发射峰强度下降。随着狭缝宽度的减小,发射峰强度下降。随着纳米银胶浓度减少,发射峰逐渐聚拢合并为426 nm的单峰,且发射峰的强度先增强后逐渐下降。通过纳米银粒子表面光电子的吸收-再发射和表面能级杂化探讨了纳米银粒子的发光机理。     

碳纳米管阴极强流脉冲发射特性实验

 在2 MeV直线感应加速器注入器平台上研究了采用浸渍涂覆方法制备的大面积碳纳米管阴极发射体的强流发射特性。研究结果表明：在脉冲高压电场下,碳纳米管阴极具有强流电子束发射能力,发射电流密度较大;碳纳米管阴极发射电子过程为场致等离子体发射。实验过程中,阴极端取样电阻环收集到的最大发射电流达350 A,阳极端法拉第筒收集的发射电流为167 A,最大阴极发射电流密度为19.4 A/cm²。