立方体AgBrCl硫增感光的电子行为

本文利用微波吸收相敏检测技术 ,同时获得了立方体AgBrCl乳剂中 ,在增感温度增加的条件下 ,自由光电子和浅束缚光电子的时间衰减曲线 ,分析了不同的硫增感产物随增感温度增加所起的陷阱效应。结果表明 ,在立方体AgBrCl乳剂中 ,硫增感初始阶段的增感产物主要是作为浅电子陷阱存在 ;随着增感温度增加至5 5℃时 ,增感产物浅电子陷阱效果最佳 ;如增感温度进一步增加 ,硫增感中心又变为深电子陷阱。文中还讨论了浅电子陷阱中浅束缚光电子衰减时间与阱深的依存关系。     

Etude par thermoluminescence de l'hydration de l'aliminate tricalcique

Thermoluminescence shows that the hydration of tricalcium aluminate is deeply influenced by structural defects of the solid. Hydration reaction excites centers of the solid detected by thermoluminescence; this energy storage is related to trapped electrons. Hydration of tricalcium aluminate in the presence of gypsum is not influenced by traps but thermoluminescence allows to corroborate the well-known mechanism of this reaction.     

The color-tunable persistent luminescence of Pr3+-activated Ca2Sb2O7 with double anti-counterfeiting potentiality

The persistent luminescence (PersL) materials Ca₂Sb₂O₇:Pr³⁺ were prepared by traditional high-temperature solid-state method. We systematically investigated the crystal structure, band structure, photoluminescence, PersL performance by X-ray diffraction diagrams, Materials Studio calculation, photoluminescence (PL) spectra, PersL spectra and CIE coordinate analysis. The PL and PersL are attributed to the Sb⁵⁺ → O^2? transition of the matrix and the 4f-4f transition of Pr³⁺ ion. For the sake of explaining the impact of various traps on PersL performance, thermoluminescence (TL) tests were performed on the optimal sample after diverse charging and discharging times. It was concluded that shallow traps have priority over deep traps in capturing electrons, and the electrons in the shallow traps were preferentially released. The highlight of this work is that the PL and PersL color can be adjusted by regulating the Pr³⁺ doping concentration when these samples were excited by a single excitation wavelength, so as to achieve a double anti-counterfeiting effect. Furthermore, the color change of PersL is different from that of PL. The luminescent patterns can make a difference as the change of concentration and time, forming a dynamic anti-counterfeiting mark that distinguishes in color and time. Thus, Ca₂Sb₂O₇:Pr³⁺ has a bright application prospect in dynamic anti-counterfeiting field.     

Formation and inhibition of free radicals in electrically stressed and aged insulating polymers

Previous work has shown that prebreakdown, electrical aging, and breakdown phenomena are directly associated with charge carriers injected from electrical contacts and their subsequent dissociative trapping and recombination. In addition, the energy released from each trapping or recombination event is dissipated in the breaking of the bonds of macromolecules, thus forming free radicals and new traps in the electrically stressed insulating polymers, as predicted by Kao's model. It is this gradual degradation process that leads to electrical aging and destructive breakdown. New experimental results are presented to confirm previous findings and a new approach to inhibit the degradation process by the incorporation of suitable dopants into the polymer. The concentration of free radicals in the polymer increases with an increasing electric field at a fixed stress time of 250 h and with increasing stress time at a fixed electric field of 833 kV cm^?1. The concentration of free radicals is directly related to the concentration of new traps created by stress. However, when suitable dopants are incorporated, the initiation voltage for the occurrence of electrical treeing and the breakdown strength are both increased. The dopants tend to create shallow traps and have little effect on the deep trap concentration. This implies that the dopants act as free‐radical scavengers that tend to satisfy the unpaired electrons of the broken bonds, which create new acceptor‐like electron traps and new shallow traps. By doing so, the shallow traps screen the deep traps, thereby reducing the energy released during trapping and recombination and the probability of breaking the macromolecular bonds and causing structural degradation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3416–3425, 2003     

Thermoluminescence of Vitreous Germanium Oxide Containing the Impurity Aluminum

The introduction of between 0 and 5% alumina into vitreous germanium oxide produces a thermoluminescence phenomenon after excitation by ultraviolet radiation which is characterized by (1) a peak position between 50° and 70° C. and (2) a peak height increasing with increase in the alumina introduced into the GeO₂ glass.     

Combustion synthesis and structural characterization of YAG: Influence of fuel and Si doping

Yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) was synthesized by low-temperature combustion synthesis (CS) with different fuels such as urea, glycine, and ammonium acetate. It has been observed that combination of urea and glycine fuels results in the formation of YAG with some impurity phase. The effect of Si incorporation in the process was studied. The combustion synthesis from mixed fuels and silica was found superior for low-temperature synthesis of pure YAG at without further heat treatment. Phase evolutions and results of flame temperature measurements are reported. Rietveld refinement and analytical calculation of different structural parameters were performed to get proper notion about Si substitution in host matrix. The thermoluminescence (TL) of materials caused by UV irradiation was used to elucidate the nature of traps. The TL analysis revealed the presence of shallow traps whose amount grew with Si doping.     

卤化银微晶中浅电子陷阱的阈值效应

依据描述卤化银微晶中光生载流子的微观动力学过程的基本模型 ,分析了自由光电子衰减时间随浅电子陷阱深度和密度的变化情况 ,从而对浅电子陷阱的阈值效应进行了讨论 ,给出了确定卤化银乳剂中浅电子陷阱最佳掺杂条件的依据。     

The Kinetics of Gamma-Ray Induced Coloring of Glass

When glasses are colored by ionizing radiation the induced optical absorption increases as the radiation progresses and appears to be due to the superposition of a number of individual absorption bands. A detailed study of this process has been made using a specimen of Corning boro-silicate glass colored by exposure to ⁶⁰Co gamma rays. This particular sample was chosen because only four bands are formed. If it is assumed that each band is Gaussian shaped the spectrum may be separated into four absorption bands. The peak energy E₀ and full width U of these bands are, in electron volts: E₀= 4.85, U = 1.19; E ₀= 3.95, U = 1.30; E _o= 2.58, U = 0.58; E₀= 2.02, U = 0.52. For each band growth curves may be constructed showing how the density of absorption centers increases as a function of dose. These growth curves have been fitted with theoretical curves based on the following considerations: the radiation field creates ionization electrons in the glass; for each ionization electron one electron deficient region or hole is formed; absorption bands observed are due to centers formed by electron trapping although the possibility that some of the bands are due to hole trapping is not ruled out; and competition for ionization electrons exists between holes and the various kinds of electron traps. Satisfactory agreement between the observed and calculated curves is obtained. The theory indicates that the "radiation protection" imparted to glass by materials such as CeO₂ may arise in several different ways and that it would be possible to decide between them from rather simple experiments.     

Synthesis and Photochemistry of Quantum-Size Semiconductor Particles in Solution and in Modified Layers

We describe the preparation of highly monodisperse, quantum-size CdS particles. In these samples a band splitting into discrete exciton-like states is observed. A mechanism for the excitonic fluorescence is presented involving shallow traps as a reservoir for electrons which finally recombine with free positive holes across the bandgap. Quantum-size CdS and PbS particles prepared in situ on highly porous, polycrystalline TiO₂ electrodes work as highly efficient sensitizers. Photocurrent yields of more than 70% are reported. In the case of PbS, it is shown that an efficient electron transfer is possible only with particles in the size of the quantization regime.     

Near edge X-ray absorption fine structure spectroscopic and infrared reflection absorption spectroscopic studies of surface modification of poly(butylene terephthalate) induced by UV irradiation

Surface modification of poly(butylene terephthalate) (PBT) induced by ultraviolet (UV) irradiation was investigated using near edge X-ray absorption fine structure spectroscopy (NEXAFS) and infrared reflection absorption spectroscopy (IRAS). UV irradiation drastically altered carbon and oxygen K-edge NEXAFS spectra of PBT. NEXAFS spectra obtained after UV irradiation were compared with those of various molecules containing carbonyl, carboxylic, ester, and anhydride groups. UV-irradiated PBT surfaces had similar spectral features to pyromellitic dianhydride, which contains anhydride groups. IRAS spectra of PBT surfaces were also changed by UV irradiation. The changes indicate that UV irradiation destroyed alkyl chains and changed the ester bond structure. These results indicate that UV irradiation removes alkyl chains and ester bonds in PBT and forms anhydride groups on PBT surfaces. It was also suggested that anhydrides might be formed near PBT surfaces by UV irradiation.     

Ultraviolet‐radiation‐induced graft copolymerization of methyl acrylate onto the sodium salt of partially carboxymethylated guar gum

In an attempt to modify the sodium salt of partially carboxymethylated guar gum (Na‐PCMGG; degree of substitution = 0.291), we studied the ultraviolet‐radiation‐induced graft copolymerization of methyl acrylate with ceric ammonium nitrate as a photoinitiator. The influence of the grafting yield was studied as a function of the different reaction parameters, and the optimum reaction conditions for photografting were determined. The various reaction parameters included the photoinitiator, nitric acid, and monomer (methyl acrylate) concentrations, the reaction time, the temperature, and the amount of the substrate. A kinetic scheme for photografting copolymerization was proposed, and the results were in good agreement with the kinetic scheme. The graft copolymerization of methyl acrylate onto Na‐PCMGG (degree of substitution = 0291) in the presence and absence of ultraviolet radiation was also carried out for the study of the efficiency of the photoinitiator. The influence of carboxymethyl groups added to the guar gum molecule on its behavior toward ultraviolet‐radiation‐induced grafting with methyl acrylate was also investigated. The evidence of photografting was ascertained with IR spectroscopy and scanning electron microscopy techniques. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1977–1986, 2005     

Thermoluminescence and reactivity of calcium sulphate hemihydrate

The influence of methods of preparation of calcium sulphate hemihydrate on its rehydration kinetics is studied using thermoluminescence. The different treatments modify the number of traps. There exists a relation between the concentration of a defect in the calcium sulphate hemihydrate and the parameters of the hydration kinetics, measured by calorimetry. The obtained differences cannot be related to the variation of specigic surface.     

浅电子陷阱掺杂剂——Ru(Ⅱ)的应用研究

研究了浅电子陷阱掺杂剂———钌盐Ru (Ⅱ )加入纯溴立方体乳剂中 ,对感光度的影响 ,结果表明在乳剂颗粒的一定位置 ,掺杂一定量钌盐能明显提高乳剂感光度。     

A Techno‐Economic Analysis of Chemical Processing with Ionizing Radiation

Photons and electrons with energies above the ionization potential of most atoms can be used to facilitate chemical reactions not otherwise possible thermochemically or under more preferable process conditions. An analysis and comparison of the economics of using sources of ultraviolet photons, high‐energy electrons, γ‐rays, and X‐rays in a chemical conversion process is presented. In many processes where the penetration depth is sufficient, the overall production costs for equivalent products are lowest for electron‐beam based systems followed, in order, by ultraviolet, gamma rays from ⁶⁰Co, and X‐ray sources. In process applications where large volume, high pressure, chemical reactors are required, gamma radiation has potential design advantages provided commercial gamma sources of lower cost than ⁶⁰Co become available.     

Positron annihilation measurements and their application to thermosets

Positrons which annihilate with electrons in solids usually give rise to two gamma rays, each with an energy close to 0.511 MeV, which are emitted in almost exactly opposite directions. The spread of the energies about the nominal value, which amounts to a few keV, is a Doppler effect reflecting the velocities along the direction of gamma emission of the electrons with which the positrons happen to annihilate. Thus the shape of the annihilation line gives a weighted measure of the electron momentum distrubution, emphasising the conduction electrons and the loosely bound localised electrons. The Positron Annihilation Techniques (PAT) allow this distribution to be determined non-destructively, and lend themselves to comparative measurements. If some of the positrons are trapped at negatively charged sites within a solid the annihilation radiation will reflect both the changed momentum distribution of the electrons seen at the trapping sites and the relative number of positrons which are trapped at the time of annihilation. To be effective the traps must have a mean spacing < 100 nm, but the sensitivity of PAT to atomic scale traps such as vacancies can nevertheless be very high. Finally, in materials containing few free electrons, information can be extracted from the formation of the positron analogue of the hydrogen atom, positronium. With standard positron sources probing depths in plastics can be a few millimetres. The PAT techniques have already proved their worth in investigations of electron momentum distributions in ordered solids, and in investigations of phase changes and of mechanical and fatigue damage in metals and alloys. Their out-of-the-way combination of characteristics makes them well worth consideration in other materials applications when conventional techniques run into difficulties.     

Induction period of hydration of tricalcium silicate

The length of the induction period of tricalcium silicate hydration has been found to be related to the probability of escape of trapped electrons measured by thermoluminescence on anhydrous sample. Several strong experimental evidences suggest an analogy between the hydration of tricalcium silicate with water vapour and the main reaction of the induction period in paste.On this basis a mechanism is tentatively proposed.     

Ultraviolet‐curable epoxidized sunflower oil/organoclay nanocomposite coatings

Hybrid nanocomposite coating films, prepared by the incorporation of epoxidized sunflower oil into organoclay, can be cured by ultraviolet radiation with either cationic or hybrid initiation. The organoclay used in this study was prepared by a cationic exchange process in which sodium ions were replaced by alkyl ammonium ions. The effects of types of photoinitiators on energy consumption in the curing process were studied. Formulations with a hybrid photoinitiator required less energy in the curing process than those with a cationic photoinitiator. Moreover, the physical properties of dried films were examined as a function of the organoclay incorporation, and it was found that the hardness of the films increased as the amount of organoclay in the formulation increased. The X‐ray diffraction patterns of an ultraviolet‐curable organoclay‐incorporated film showed an exfoliated structure of the organoclay in the ultraviolet‐curable coating film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydration of tricalcium silicate by water vapour

The influence of the cooling rate of tricalcium silicate samples on the velocity of hydration by water vapour is studied using thermoluminescence techniques. Thermal treatment processings modify the probability of escape of trapped electrons and the characteristics of the centres. The electrons of the first trap (peak I) have a marked influence on the rate of water chemisorption on tricalcium silicate. Quantitative relationships show the importance of the nucleophilic excited centres in the hydration reaction. Moreover this hydration reaction was found to be limited to chemisorptive bond formation on these reactive sites and does not extend to the whole surface.     

硫增感AgBrI T颗粒乳剂光电子行为研究

利用微波相敏技术，获得了硫增感AgBrI T颗粒乳剂中自由光电子和束缚光电子时间衰减信号，分析了光电子衰减时间、电子陷阱效应、光电子寿命、有效陷阱深度及束缚电子转移时间与增感时间的关系，获得了最佳的增感时间、衰减时间、电子陷阱效应、光电子寿命、有效陷阱深度和转移时间数值，     

Dynamics and reactivity of trapped electrons on supported ice crystallites

The solvation dynamics and reactivity of localized excess electrons in aqueous environments have attracted great attention in many areas of physics, chemistry, and biology. This manifold attraction results from the importance of water as a solvent in nature as well as from the key role of low-energy electrons in many chemical reactions. One prominent example is the electron-induced dissociation of chlorofluorocarbons (CFCs). Low-energy electrons are also critical in the radiation chemistry that occurs in nuclear reactors. Excess electrons in an aqueous environment are localized and stabilized by the local rearrangement of the surrounding water dipoles. Such solvated or hydrated electrons are known to play an important role in systems such as biochemical reactions and atmospheric chemistry. Despite numerous studies over many years, little is known about the microscopic details of these electron-induced chemical processes, and interest in the fundamental processes involved in the reactivity of trapped electrons continues. In this Account, we present a surface science study of the dynamics and reactivity of such localized low-energy electrons at D(2)O crystallites that are supported by a Ru(001) single crystal metal surface. This approach enables us to investigate the generation and relaxation dynamics as well as dissociative electron attachment (DEA) reaction of excess electrons under well-defined conditions. They are generated by photoexcitation in the metal template and transferred to trapping sites at the vacuum interface of crystalline D(2)O islands. In these traps, the electrons are effectively decoupled from the electronic states of the metal template, leading to extraordinarily long excited state lifetimes on the order of minutes. Using these long-lived, low-energy electrons, we study the DEA to CFCl(3) that is coadsorbed at very low concentrations (～10(12) cm(-2)). Using rate equations and direct measurement of the change of surface dipole moment, we estimated the electron surface density for DEA, yielding cross sections that are orders of magnitude higher than the electron density measured in the gas phase.