Optical excitation of trapped charges in quartz, potassium feldspars and mixed silicates: The dependence on photon energy

Optical excitation of trapped charges has been studied by stimulating them with photons of energies from 1.8 to 2.7 eV and measuring the resulting luminescence at higher photon energies. The samples studied were quartz, potassium feldspar and fine-grained silicate extracts from natural sediments. The initial luminescence intensity and its decay as the traps are emptied have been used to gain information about the traps contributing to the emission. For the quartz studied the data are well explained by excitation from a single trap. The excitation spectra for potassium feldspars and mixed silicates show evidence of two different traps, the deepest of which is seen to give rise to the most luminescence. Its optical trap-depth may be more than 2.4 eV while the depth of the shallow trap appears to be about 2.1 eV. In nature, the deeper trap will probably not be well bleached during deposition in all aqueous environments, and for optical dating of water-laid sediments selective sampling of the shallow trap photons with energies less than 2.3 eV for stimulation may prove beneficial.     

On luminescence stimulated from deep traps using thermally-assisted time-resolved optical stimulation in α-Al2O3:C

We report a study of charge transfer mechanisms of electrons stimulated optically from very deep traps, also known as donor traps, in α-Al₂O₃:C. The investigations were carried out using thermally-assisted time-resolved optical stimulation, thermoluminescence and by way of residual thermoluminescence from the main electron trap. When the charges are optically stimulated from the deep traps, they are redistributed via the conduction band to the main electron trap and the shallow trap from where they are optically or thermally released for recombination at luminescence centres. The luminescence is strongly quenched at high measurement temperature as evident by very short luminescence lifetimes at these temperatures. The main peak due to residual thermoluminescence is located at a higher temperature than the conventional main peak.     

Valence band contributions to photoluminescence excitation spectra of tightly bound holes in zincblende semiconductors

Photoluminescence excitation (PLE) spectra of deep acceptor states in ZnSe, for example the Cu-related luminescence band at ≈1.95 eV, contain a prominent excitation band at ≈3.25 eV. This band lies above the structure marking the lowest direct E_O band gap E_g by the spin-orbit splitting energy Δ of the valence bands at Γ. The higher energy feature is either absent or greatly de-emphasised in the PLE spectra of shallow acceptor states in ZnSe and of the oxygen iso-electronic trap in ZnTe, where the electron rather than the hole is tightly bound. However, a significant PLE component at E_g + Δ is observed for deep acceptor-like states in ZnTe, where Δ is ≈0.95 eV. Efficient PLE at E + Δ for luminescence from deep acceptor-like states is shown to be consistent with the extended wave-vector contributions to the bound state wave-functions of holes of binding energies ≈Δ.     

Mechanism Underlying the Recombination of Nonequilibrium Charge Carriers Localized at Deep Traps in Silver Chloride

A procedure for investigating the mechanism of decrease in the population of deep local states on excitation of a crystal with light has been developed. It is based on studying the action of an electric field on the rate of decrease in the light sum of a photostimulated burst of luminescence. A number of experimental techniques have also been used, in particular, investigation of the kinetics of the decrease in the concentration of charge carriers localized at the trapping levels depending on their depth in the forbidden band and also the influence of IR radiation with an energy of 0.1– 0.4 eV on this process. It is shown that the main contribution to the decrease in the concentration of the electrons localized at deep traps is made by their recombination with the holes thermally released from the localization levels of depth ∼kT. It is inferred that a radiationless mechanism of this recombination is the most probable one.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 2, pp. 213–217, March–April, 2005.     

An algorithm for unified analysis on the thermoluminescence glow curve

An algorithm was developed to integrally handle excitation by radiation, relaxation and luminescence by thermal or optical stimulation in thermoluminescence (TL) and optically stimulated luminescence (OSL) processes. This algorithm reflects the mutual interaction between traps through a conduction band. Electrons and holes are created by radiation in the beginning, and these electrons move to the trap through the conduction band. These holes move to the recombination center through a valence band. The ratio of the electrons allocated to each trap differs with the recombination probability and these values also relevant to the process of luminescence. Accordingly, the glow curve can be interpreted by taking the rate of electron–hole pairs created by ionizing radiation as a unique initial condition. This method differs from the conventional method of interpreting the measured glow curve with the initial electron concentration allocated to each trap at the end of irradiation. A program using the Visual Studio's C# subsystem was made to realize such a developed algorithm. To verify this algorithm it was applied to LiF:Mg,Cu,Si. The TL glow curve was deconvoluted with a model of five traps, one deep trap and one recombination center (RC).     

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I--V (current--voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.     

Influence of surface states on deep level transient spectroscopy in AlGaN/GaN heterostructure

Deep level transient spectroscopy(DLTS) as a method to investigate deep traps in AlGaN/GaN heterostructure or high electron mobility transistors(HEMTs) has been widely utilized.The DLTS measurements under different bias conditions are carried out in this paper.Two hole-like traps with active energies of E_v + 0.47 eV,and E_v + 0.10 eV are observed,which are related to surface states.The electron traps with active energies of E_c-0.56 eV are located in the channel,those with E_c-0.33 eV and E_c-0.88 eV are located in the AlGaN layer.The presence of surface states has a strong influence on the detection of electron traps,especially when the electron traps are low in density.The DLTS signal peak height of the electron trap is reduced and even disappears due to the presence of plentiful surface state.     

Photoionization spectra of silver dimers adsorbed on the surface of a ZnS single crystal

We use the photostimulated luminescence flash method to measure photoionization spectra of Ag₂ clusters adsorbed on the surface of a ZnS single crystal. Adsorbed dimers of silver are prepared by treatment of the surface of a ZnS single crystal in high vacuum with a beam of molecular Ag ₂ ⁺ ions followed by their neutralization. We show that the adsorbed dimers create two types of electron traps at energy levels 1.63 and 1.82 eV below the bottom of the conduction band. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 545–547, July–August, 2007.     

Luminescence of silver chloride microcrystals upon photoexcitation by different methods

The luminescence spectra of AgCl microcrystals were measured in two different regimes: in the regime of excitation of stationary luminescence and in the regime of photostimulated burst of luminescence. Differences between the spectra of stationary luminescence and the spectra of photostimulated-luminescence burst in the range between 430 and 590 nm have been found. The luminescence spectra are complex; the ratio of intensities for elementary components changes with the technique of excitation. Differences in the form and composition of complex luminescence bands obtained under different conditions of registration are attributed to the recombination interaction of the luminescence centers. It is shown that analysis of the dependences of intensity ratios for the elementary components of a complex luminescence band on the exciting-radiation intensity allows one to evaluate the mechanism of recombination in elementary bands provided that the mechanism is known for at least one luminescence band.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 85–89. January–February, 2005.     

掺杂型BaFBr:Eu2+的热释发光性质的研究

BaFBr:Eu^2 是利用色心存储电子－空穴对并用可见光激励读出存储信息（产生Eu^2 的4f^65d→4f^7的跃迁）的优良的光激励发光材料。通过热释发光技术研究了BaFBr:Eu^2 的热激活行为，对其低温段和高温段的热释发光峰分别进行了归属，通过对BaFBr:Eu^2 以及掺杂Na^ 或Al^3 的BaFBr:Eu^2 的热释发光（TL）谱和光激励发光（PSL）谱的表征，指出在BaFBr:Eu^2 中掺杂Na^ 或Al^3 影响了F（Br^-）色心，使其陷阱深度变涛，并从理论上加以计算，得出的热致激发能量的变化与光致激光能量的变化能很好地吻合。     

The photoluminescence,afterglow and up conversion photostimulated luminescence of Eu3+ doped Mg2SnO4 phosphors

The Mg₂SnO₄:Eu³⁺ phosphor with reddish photoluminescence, green afterglow and photostimulated luminescence is obtained by the solid state method. The host related afterglow is greatly enhanced by doping of Eu³⁺ and it can last nearly 6 h when the Eu³⁺ concentration is 1 mol%. The photostimulated luminescence is found to be weakened by doping of Eu³⁺. It was revealed that all the shallow traps and a part of the deep traps are involved in afterglow. The majority of deep traps are responsible for photostimulated luminescence. The impact of doping Eu³⁺ on the afterglow and photostimulated luminescence is investigated and we propose a feasible interpretation.     

掺杂含量对环氧纳米复合电介质陷阱与空间电荷的影响

环氧纳米复合电介质具有抑制空间电荷积聚、高电阻率、高击穿强度等优异性能,对直流电力设备的发展具有重要的作用.但纳米粒子含量对纳米复合电介质陷阱、电导率和空间电荷的影响机理尚不清楚.本文在纳米复合电介质交互区结构模型的基础上提出了计算交互区浅陷阱和深陷阱密度的方法,得到了浅陷阱和深陷阱密度随纳米粒子含量的变化关系.随着纳米粒子含量的增加,浅陷阱密度逐渐增大,深陷阱先增加然后由于交互区重叠的影响而逐渐减少.研究了纳米粒子含量对浅陷阱控制载流子迁移率的影响,发现随着纳米粒子的增多,浅陷阱大幅增多,浅陷阱之间的平均间距迅速减小,导致载流子更容易在浅陷阱间跳跃迁移,浅陷阱控制载流子迁移率增大.建立了纳米复合电介质的电荷输运模型,采用电荷输运模型计算研究了环氧/二氧化钛纳米复合电介质的空间电荷分布、电场分布和电导率特性.发现在纳米粒子添加量较小时,交互区的深陷阱对电导的影响起主导作用;纳米粒子添加量进一步增加,浅陷阱对电导的影响将起到主要作用.     

Tunneling recombination luminescence in Na2O · 3SiO2 glass

The recombination luminescence exhibited by Na₂O · 3SiO₂ glass in the spectral region from 1.5 to 5.0 eV, after excitation by X-rays or quanta with energies ranging from 5.8 to 6.2 eV, consists of thermally stimulated and tunneling components. The tunneling luminescence band shape depends on the population of various depth traps.     

聚合物材料空间电荷陷阱模型及参数

采用电声脉冲测量技术研究了直流电场下低密度聚乙烯材料的电荷入陷和脱陷特征. 发现在不同电场周期下样品的电荷衰减呈现不同的特征, 为此提出了一个简单的基于两陷阱水平的入陷和脱陷模型, 并计算了相应的参数, 如陷阱能级和密度. 确定了不含任何添加剂的低密度聚乙烯样品中存在的两种水平的陷阱能级分别为: 较浅陷阱能级0.77–0.81 eV 对应的浅陷阱电荷密度为(1.168–1.553)× 10¹⁹ m^-3; 较深陷阱能级0.96–1.01 eV 对应的深陷阱电荷密度为(1.194–4.615)× 10¹⁸ m^-3. 最后初步验证了材料的深陷阱能级和对应的深陷阱电荷密度随老化而增加, 可考虑将模型中的两能级陷阱参数作为老化诊断特征参量. 关键词： 聚合物 空间电荷 陷阱 老化     

注硅半绝缘GaAs的深能级

用深能级瞬态谱(DLTS)详细研究了硅离子注入Liquid-encapsulated Czochralski(缩写为LEC)半绝缘GaAs的深中心。结果表明,在注硅并经高温退火的有源区中观测到4个多子(电子)陷阱,E₀₁,E₀₂,E₀₃和E₀₄。它们的电子表观激活能分别为0.298,0.341,0.555和0.821eV。其中E₀₄与EL2有关,但不是EL2缺陷。E₀₄的电子 关键词：     

GdVO4:Eu3+的热释光研究

GdVO4:Eu^3 有着十分优良的发光特性，它发光强度高，特别是具有很好的温度特性，在室温以上发光强度随温度的升高而增强，很利于在高温下使用此材料。本文对它的热释光进行了研究，其热释光峰值分别位于193，235和304K，根据计算可知它们的陷阱深度分别为0.39,0.47和0.61eV，陷阱的主要来源可能是F^ ,F和钒空位；Eu^3 掺入导致的晶格畸变，其中最主要的来源可能是空位导致的。     

The contribution of hole traps to thermoluminescence of the dosimetric peak in anion-defect α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> single crystals

The thermoluminescent properties of anion-defect alumina single crystals with different FWHMs of the main (dosimetric) peak at 400–500 K are studied. New experimental evidence in favor of the hole nature of traps associated with the high-temperature part of this peak are presented. The introduction of hole trap centers into analysis provided theoretical justification for the experimentally observed dependences of the thermoluminescence (TL) intensity, the temperature position of the main peak, and its FWHM on the occupancy of deep traps. The hole nature of traps of the high-temperature part of the main TL peak is confirmed by the results of examination of specific TL features of shallow trap centers, which govern TL at 350 K, and the temperature variation of the main TL peak spectrum.     

感绿光谱增感染料在氯化银微晶表面的电子陷阱效应

光谱增感技术可使卤化银感光材料实现对全波段感光，同时光谱增感技术在现代光信息记录与存储、光电器件、太阳能转换与存储等领域具有重要的应用.应用微波吸收介电谱技术研究了立方体氯化银吸附感绿菁染料后的光电子衰减特性，建立了氯化银光电子衰减动力学模型，根据此模型结合光电子衰减实验结果对光谱增感染料吸附在卤化银表面的电子陷阱效应进行了分析.研究结果表明：当染料以单分子态吸附在卤化银表面时，染料起浅电子陷阱效应；染料以J聚集体吸附在卤化银表面时，染料起到了深电子陷阱效应.浅电子陷阱与深电子陷阱效应的临界浓度为每40g 关键词： 感绿染料 氯化银 光电子衰减 电子陷阱效应     

The effects of deep trap population on the thermoluminescence of Al2O3:C

The influence of deep traps on the 450 K thermoluminescence (TL) peak of Al₂O₃:C is studied. Depending upon the sample and on the degree of deep trap filling, features such as the TL width, area and height can vary considerably. These effects are interpreted to be due to: (a) sensitivity changes introduced by competition mechanisms involving deep electron and hole traps, and (b) the multiple component nature of the 450 K TL peak. The influence of the deep traps on the TL was studied using different excitation sources (beta irradiation or UV illumination), and step annealing procedures. Optical absorption measurements were used to monitor the concentration of F- and F⁺-centers. The data lead to the suggestion that the competing deep traps which become unstable at 800–875 K are hole traps, and that the competing deep traps which become unstable at 1100–1200 K are electron traps. Both the dose response of the TL signal and the TL sensitivity are shown to be influenced by sensitization and desensitization processes caused by the filling of deep electron and hole traps, respectively. Changes in the TL peak at low doses were also shown to be connected to the degree of filling of deep traps, emphasizing the influence of deep trap concentration and dose history of each sample in determining the TL properties of the material. Implications of these results for the optically stimulated luminescence properties are also discussed.