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AgBrIT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.     

纳米硫化铅增感的溴化银微晶中光电子衰减特性研究

采用纳米硫化铅作为增感剂对边长为0.8μm的溴化银立方体颗粒进行了化学增感.利用微弱信号的微波吸收相敏检测技术,在超短脉冲激光作用下,获得了立方体溴化银乳剂中自由光电子和浅束缚光电子随增感时间变化的衰减曲线.通过测量溴化银光作用过程的时间分辨谱,讨论了卤化银晶体中电子陷阱对光电子运动行为的影响,分析了电子陷阱效应同增感时间之间的关系以及两个一级衰减区间寿命值同增感时间的关系.通过未增感样品与增感样品的衰减曲线对比,得到了在此实验条件下的最佳增感时间为60 min.     

溴碘化银核壳乳剂中电子的捕获和复合

本文应用双注仪制备了在核表面进行不同程度还原增感和一系列溴碘化银核壳乳剂,在不同条件下测定了核表面形成的不同还原增感中心对乳剂微晶光电子衰减动力学及发光光谱的影响。结果表明:在一定增感温度和时间条件下,当Na₂SO₃用量低于5.4mg/molAg时光电子衰减动力学为二级反应,而当Na₂SO₃用量超过27mg/molAg时,增感中心一部分作为空穴陷阱,另一部分作为电子陷阱,光电子衰减速率决定于电子的捕获和复合,光电了衰减动力学为一复杂过程。低温发光光谱随不同增感程度的改变证明:还原增感中心不是发光中心。     

染料增感AgBr乳剂的光电子衰减动力学研究

本工作利用微波吸收薄膜介电谱测量技术,测量了菁染料光谱增感后的AgBr晶体乳剂在脉冲激光曝光后产生的光电子衰减时间特性,分析了不同类型的染料及其增感条件对材料光电子时间特性的影响关系.通过比较增感后的T 颗粒乳剂和立方体乳剂的光电子衰减特性,实验验证了吸附在T 颗粒(111)晶面上的染料比吸附在立方体(100)晶面上的染料更有效、更有助于形成潜影的论据.     

用计算机模拟技术研究潜影形成机理 Ⅲ.化学增感对潜影形成的作用

继前文的潜影形成模型,对化学增感乳剂进行了计算机模拟研究。结果如下:(1)硫增感引入大的浅陷阱,可增加敏度与改善低照互易律失效;其空穴陷阱的作用则不是很有效。(2)金增感除了减小可显影中心的尺寸和增加抗氧化能力外,还应有另外的增感机理。Ag₂经金强化可以部分地转化为可显影中心。(3)还原增感斑与尺寸相同的曝光产生的银斑性质相同,曝光时大部分还原增感斑被破坏掉了,只有极少数有机会长大。还原增感斑的两个重要作用:提高了形成潜影的概率;消耗空穴或光解溴,使颗粒中的净剩电子增多。二者对潜影形成都有重要贡献。     

曝光强度对卤化银微晶中载流子行为及其陷阱效应的影响

针对卤化银感光材料潜影形成过程中光作用动力学问题,分析了曝光强度对光生载流子行为和电子陷阱效应的影响,认为伴随着曝光强度的增加,影响光电子衰减的因素由电子陷阱起主要作用演化到电子陷阱和复合中心共同起作用进而演化到复合中心起主要作用.     

卤化银微晶体的光电子行为

卤化银乳剂微晶体的光电子行为是影响照相感光度的重要因素,本文就光电子研究方法、光电子衰减、电子陷阱、本征与外来带电中心对光电子衰减与寿命的影响以及光电子行为与其它物理性质的关系等方面加以综述.     

立方体溴化银颗粒光谱增感的电子转移超快动力学研究

本文利用皮秒时间分辨条纹相机技术检测了3种染料在立方颗粒溴化银上吸附后形成聚集体的荧光光谱,分析了3种染料在不同染料浓度下对染料聚集体到溴化银导带的超快电子转移过程的影响,进而分析其对增感效率的影响关系,并探讨了增感过程的微观机理.实验结果表明,荧光衰减的动力学曲线与一个双指数函数拟合得相当好,存在一快一慢两个衰减成分,快衰减成分占拟合较大比例,表明其源于与荧光衰减相竞争的从激发态染料聚集体到AgBr导带的电子转移.光致电子转移的速率及增感效率随着染料相对浓度的增加表现出一定的变化趋势,染料浓度增加,增感效率减小.     

溴碘化银T-颗粒乳剂晶体的表面形貌研究

用原子力显微镜研究了T-颗粒卤化银晶体、掺杂有浅电子陷阱掺杂剂K₄[Ru(CN)₆]的掺杂乳剂晶体、经硫加金化学增感后的掺杂乳剂晶体的表面形貌以及曝光后表面形貌的变化.观察结果表明,T-颗粒晶体表面存在很多突起,经曝光后这些突起高度增加,更集中.掺入浅电子陷阱掺杂剂K₄[Ru(CN)₆]后,T-颗粒晶体对光更敏感,曝光后表面突起高度的增加幅度大于未掺杂乳剂光照后表面高度的变化.同时硫增感剂对表面突起的分布也有很大的影响.     

卤化银乳剂制备中的新型掺杂剂

本文综述了近年来乳剂制备中常用的新型掺杂剂,较详细地介绍了两种能提高光电子利用效率的掺杂剂,即过渡金属络合物浅电子陷阱掺杂剂和羧酸盐(酯)有机空穴陷阱掺杂剂,总结了掺杂剂的选择原则,并举例说明了掺杂剂对乳剂感光度的影响.     

Mapping of the Photoinduced Electron Traps in TiO2 by Picosecond X‐ray Absorption Spectroscopy

Titanium dioxide (TiO₂) is the most popular material for applications in solar‐energy conversion and photocatalysis, both of which rely on the creation, transport, and trapping of charges (holes and electrons). The nature and lifetime of electron traps at room temperature have so far not been elucidated. Herein, we use picosecond X‐ray absorption spectroscopy at the Ti K‐edge and the Ru L₃‐edge to address this issue for photoexcited bare and N719‐dye‐sensitized anatase and amorphous TiO₂ nanoparticles. Our results show that 100 ps after photoexcitation, the electrons are trapped deep in the defect‐rich surface shell in the case of anatase TiO₂, whereas they are inside the bulk in the case of amorphous TiO₂. In the case of dye‐sensitized anatase or amorphous TiO₂, the electrons are trapped at the outer surface. Only two traps were identified in all cases, with lifetimes in the range of nanoseconds to tens of nanoseconds.     

Spectra of trapped electrons in irradiated rigid media

In the irradiated polar systems, the blue shifts of the absorption spectra of trapped electrons (e _t ⁻ ) have as yet been observed by pulse radiolysis in the milisecond time range. This fact has been ascribed to the reorientation of the matrix polar molecules under the influence of the coulombic electron field. In order to check whether the spectral changes of e _t ⁻ are limited to very short times only, the spectra of e _t ⁻ in frozen 8M NaOH, 95% ethylene glycol (EG), 95% methanol, 95% ethanol, 95% n-propanol, 95% isopropanol, 95% butanol (+5% H₂O) were examined at the liquid nitrogen temperature by applying the stationary γ-radiolysis. Except for 8M NaOH and 95% EG, in the remaining matrices the shifts of e _t ⁻ spectra towards the short wavelengths were observed within 24 hrs after irradiation. The less polar the matrix, the larger was the spectral shift. The observed effect seems to indicate that the reorientation process takes place in times much longer than these measured by pulse radiolysis. After the addition of scavengers the lowering of the initial absorption occured in all investigated systems. This was ascribed to the reaction of “dry” electrons with the scavengers. Moreover, the results obtained by the pulse radiolysis of ethanol indicate that the presence of scavengers accelerates the decay of the infrared part of the trapped electron spectrum. The “infrared electrons” (located in shallow traps) neither react with the scavenger nor deepen their traps by reorientation. Most probably in the presence of scavengers these electrons recombine with positive ions via tunneling.     

Quadrupolar traps for charge carriers in the vicinity of lattice vacancies in pentacene crystals

Thermally stimulated current techniques have been used for a selective study of shallow electron and hole traps in pentacene crystals. Asymmetry, observed in electron and hole trapping, is interpreted as evidence for the existence of quadrupolar traps in the vicinity of lattice vacancies, theoretically predicted by Eisenstein and Munn.     

Graphene quantum dots assisted photovoltage and efficiency enhancement in CdSe quantum dot sensitized solar cells

CdSe quantum dot sensitized solar cells(QDSCs) modified with graphene quantum dots(GQDs) have been successfully achieved in this work for the first time. Satisfactorily, the optimized photovoltage(Voc) of the modified QDSCs was approximately 0.04 V higher than that of plain CdSe QDSCs, consequently improving the photovoltaic performance of the resulting QDSCs. Served as a novel coating on the CdSe QD sensitized photoanode, GQDs played a vital role in improving Vocdue to the suppressed charge recombination which has been confirmed by electron impedance spectroscopy as well as transient photovoltage decay measurements. Moreover, different adsorption sequences, concentration and deposition time of GQDs have also been systematically investigated to boost the power conversion efficiency(PCE) of CdSe QDSCs. After the coating of CdSe with GQDs, the resulting champion CdSe QDSCs exhibited an improved PCE of 6.59% under AM 1.5G full one sun illumination.     

Investigation on relation between TL and OSL of Li2B4O7:Cu, In

Polycrystal Li₂B₄O₇ (LBO) doped with Cu and In was prepared and then sintered at different temperatures. X-ray diffraction (XRD) was applied to get the parameters of the LBO structure, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured, and a second-order exponential decay model was fitted to the OSL decay curves. The results indicate that the original number of OSL traps that have captured electroncs is linearly related with the sum of TL decay during the OSL process. Mean decay constant of OSL is related to the sintered temperature. The possible reason is that the sintered temperature affects the crystal sizes of the polycrystal, and consequently affects the stimulating lights’s intensity and the photoionization cross-section of the electrons, which have been captured by the traps. __________ Translated from Acta Scientiarum Naturalium Universitatis Sunyatseni, 2005, 44(4) (in Chinese)     

Partially hydroxylated polycrystalline ionic oxides: a new route toward electron-rich surfaces

Charge traps at the surface of oxide materials play a fundamental role in various chemical processes, such as the activation of supported metal clusters. In this study, combining electron paramagnetic resonance with cluster model DFT calculations, we show that excess electrons at the surface of MgO, CaO, and SrO polycrystalline materials can be generated by preparing weakly hydroxylated surfaces followed by deposition of small amounts of alkali metals. The residual OH groups present on specific sites of the partially dehydroxylated surface act as stable traps for electrons donated by the alkali metal (Na in this case) which forms a Na+ ion distant from the trapped electron. This process results in the formation of thermally stable (H+)(e-) color centers at the surface of the oxide. The procedure could be of interest for the stabilization and activation of supported metal nanoparticles with potential use in catalysis.     

Low energy charged particles interacting with amorphous solid water layers

The interaction of charged particles with condensed water films has been studied extensively in recent years due to its importance in biological systems, ecology as well as interstellar processes. We have studied low energy electrons (3-25 eV) and positive argon ions (55 eV) charging effects on amorphous solid water (ASW) and ice films, 120-1080 ML thick, deposited on ruthenium single crystal under ultrahigh vacuum conditions. Charging the ASW films by both electrons and positive argon ions has been measured using a Kelvin probe for contact potential difference (CPD) detection and found to obey plate capacitor physics. The incoming electrons kinetic energy has defined the maximum measurable CPD values by retarding further impinging electrons. L-defects (shallow traps) are suggested to be populated by the penetrating electrons and stabilize them. Low energy electron transmission measurements (currents of 0.4-1.5 μA) have shown that the maximal and stable CPD values were obtained only after a relatively slow change has been completed within the ASW structure. Once the film has been stabilized, the spontaneous discharge was measured over a period of several hours at 103 ± 2 K. Finally, UV laser photo-emission study of the charged films has suggested that the negative charges tend to reside primarily at the ASW-vacuum interface, in good agreement with the known behavior of charged water clusters.     

卤化银感光乳剂的光致电子顺磁共振信号强度与成熟时间的关系

本文发现含染料的溴化银模型乳剂在g=2.0023下的光致ESR信号强度随化学成熟时间的增长而增强,与光敏度的变化呈平行关系。这一现象与文献中报道的^[1]在实用乳剂上得出的结果恰恰相反。假设化学敏化产物在潜影形成过程中既能作为电子陷阱,又能作为空穴陷阱,可以解释这种差异。