ZnS晶体中浅电子陷阱对光电子衰减过程的影响

本文采用微波吸收法,测量了ZnS:Mn,Cu:I,Br粉末材料受到超短激光脉冲激发后,其光生电子和浅束缚电子的衰减过程.发现制备过程中Mn2+、Cu1、I-、Br-的掺杂量对光生导带电子的衰减过程有明显的影响.光生电子寿命是I-、Br-形成的浅施主能级和Cu+受主能级、Mn2+发光中心共同作用的结果.本文还测量了材料的热释光曲线,Cu+受主能级、Mn2+发光中心会影响热释光强度,证实I-、Br-形成电子陷阱对光生电子和浅陷阱中的电子寿命有延长作用,而Mn2+发光中心会起到缩短寿命的作用.     

掺杂AgCl中光电子衰减特性研究

利用微波吸收介电谱检测技术,检测均匀掺杂[Fe(CN)_6]~(4-)盐的立方体AgCl微晶首次曝光后的自由和浅束缚光电子的衰减时间分辨谱.实验发现,随着掺杂浓度的增加,样品中自由光电子衰减时间逐渐从未掺杂时的116 ns延长至1133 ns.分析光电子衰减曲线还同时得到,随着掺杂浓度的增加,光电子的前期较慢衰减过程逐渐变快,后期较快衰减过程逐渐变慢,总体上衰减时间逐渐增加,且掺杂浓度变化对后期衰减影响较大.研究表明掺杂使得晶体中引入了能总体上延缓光电子衰减的浅电子陷阱,并且随掺杂浓度的增加,浅电子陷阱特征更加明显.     

Co掺杂对ZnO晶体中光生电子瞬态过程的影响

采用气相反应制备了ZnO和ZnO∶Co微晶,并通过热释光研究了材料中的电子陷阱能级(施主能级),采用微波介电谱研究了材料的光生电子瞬态过程.发现纯ZnO热释光谱有两个峰,分别为-183 ℃和-127 ℃,说明存在两个电子陷阱能级;而ZnO∶Co中热释光信号很弱,只有纯ZnO的十分之一.微波介电谱研究表明,由于电子陷阱对导带电子的驰豫作用,纯ZnO材料导带光电子的衰减为一级指数过程,寿命为802 ns.ZnO∶Co微晶体的最大微波介电谱强度低于纯ZnO晶体的五分之一,电子陷阱密度较小,其光生电子快速衰减,过程仅为10～20 ns.结果说明Co掺杂具有明显的抑制电子陷阱能级生成的作用.     

浅电子陷阱掺杂AgCl微晶的光作用特性研究

利用微波吸收介电谱检测技术,同步检测均匀掺杂K4Fe(CN)6盐的立方体AgCl微晶在室温条件下的自由和浅束缚光电子的衰减时间分辨谱。对比未掺杂样品发现,掺杂引入的浅电子陷阱使样品中的自由光电子衰减时间延长了338ns,衰减过程中出现一个明显的一级指数快衰减区;较高浓度掺杂情况下,测量了光作用产物对光电子衰减的影响,分析表明,光作用产物是具有深电子陷阱作用的银簇。光作用产物的出现,使得晶体中发生了浅电子陷阱到深电子陷阱效应的转变,可见掺杂使得晶体内部结构和光作用特性发生了变化。     

声化学法制备ZnS: Mn纳米晶及其光学性能

以无水氯化锌,四水氯化锰以及硫代乙酰胺为原料,采用声化学法成功制备了锰掺杂的ZnS(ZnS: Mn)纳米晶.采用透射电子显微镜镜(TEM)、X射线能谱仪(EDS)、X射线粉末衍射(XRD)和光致发光谱(PL)对所制得的纳米进行了表征.结果表明:所制备ZnS: Mn为立方闪锌矿结构,纳米粒子的形貌接近于球形.平均晶粒尺寸为10 nm左右.PL光谱分析表明:所制备试样有两个主要的发射峰,分别位于在480 nm和570 nm左右,后者与体材料ZnS: Mn相比发生了明显蓝移,但仍表现为橙黄色发光.Mn2+掺杂浓度对ZnS: Mn的光致发光性能有显著影响,原料中Zn: Mn: S(物质的量比)为3: 1: 4,Mn2+掺杂浓度为2.64 at;时,光致发光光谱发射峰强度达到最大值.     

近红外发射Lu2O3∶Mn4+荧光粉的制备及其发光特性

采用高温固态烧结方法制备了具有不同Mn4+离子掺杂浓度的Lu2O3∶x;Mn4+荧光粉.应用X射线衍射、荧光激发和发射光谱、X射线光电子能谱、扫描电子显微镜和发光动力学测量等手段研究了该荧光粉的微结构和发光特性与掺杂浓度的关系.实验结果表明,Mn4离子可掺杂到Lu2O3基质晶格中,在252 nm激发下,可观察到位于695 nm和712 nm的近红外发射峰,其分别来源于Mn4+离子的2E→4A2和4T2→4 A2的跃迁.当Mn4+掺杂浓度为0.1;时,可获得最大的发光强度.通过优化热处理条件(在空气气氛、1400℃温度下热处理5h),可进一步提高Lu2O3∶0.1; Mn4+荧光粉的近红外发光强度和余辉性能.实验发现,经热处理的Lu2O3∶0.1; Mn4+样品中,Mn4+离子占据了Lu2O3基质中的S6和C2两种格位;具有较长寿命的近红外发光来自占据S6格位Mn4离子的贡献,而具有较短寿命的近红外发光则来自占据C2格位Mn4离子的贡献.实验表明,经高温热处理的近红外发射Lu2O3∶Mn4+材料余辉时间大于3 min,其在生物成像方面有潜在的应用前景.     

Er掺杂ZnS纳米晶的合成及光致发光性能研究

以巯基乙酸(HSCH2COOH)为稳定剂,采用水热法合成了分散性好的ZnS∶ Er纳米晶,分别利用XRD、TEM,荧光光谱仪对其物相,形貌及光学性能进行了研究.结果表明:ZnS∶ Er纳米晶为闪锌矿ZnS结构,颗粒近似球形,平均粒度为5 ～8 nm.当Er3+掺杂摩尔浓度为6;,稳定剂巯基乙酸添加摩尔分数为2;,合成温度为120℃条件下得到了发光性能较好的Er离子掺杂ZnS纳米晶材料,并对其发光机理进行了探讨.     

ZnS:Mn/CdS核壳结构纳米微粒的制备及光学特性

采用微乳液法制备了掺Mn的ZnS纳米微粒并用CdS对其进行了表面修饰,以XRD、紫外吸收和发射光谱对其结构及光学性质进行了表征和研究.制得的纳米微晶粒径为4～6nm,为立方纤锌矿结构.与未经包覆的ZnS:Mn纳米微粒相比,核壳结构的ZnS:Mn/CdS纳米微粒中Mn2+发射峰的强度增强了很多,适当厚度的壳层的修饰可减少其表面态发射和非辐射跃迁,增强了Mn2+离子的4T1-6A1的能量传递和ZnS的带边发射,提高了发光效率;讨论了ZnS核中Mn掺杂浓度对ZnS:Mn/CdS纳米微晶的光学性能的影响,发现当掺Mn浓度为4;时Mn2+发射峰的强度最大.     

Y3+/Li+和Y3+/Na+双掺杂氟化钡快响应闪烁晶体

氟化钡(BaF₂)晶体是已知响应最快的闪烁晶体,在高能物理、核物理及核医学等领域有着广泛的应用前景。抑制BaF₂晶体的慢发光成分对其工程应用至关重要。本文利用坩埚下降法制备了高Y³⁺掺杂浓度5%、8%、10%(摩尔分数)的BaF₂晶体,并采用Y³⁺与碱金属离子(Li⁺、Na⁺)共掺杂的方法形成电荷补偿阻止间隙F^-的产生,制备了双掺杂型BaF₂快响应闪烁晶体,进而基于优化的5 ns和2 500 ns时间门宽测试方法,研究了Y³⁺掺杂浓度以及Y³⁺与碱金属离子(Li⁺、Na⁺)共掺杂浓度对BaF₂闪烁晶体快/慢成分比的影响规律。结果表明,生长的高浓度Y³⁺掺杂BaF₂晶体的光学质量优异,在220 nm和300 nm处透过率分别高于90%和92%;随着Y³⁺掺杂浓度由0提高至10%,BaF₂晶体的慢发光成分显著降低,快/慢成分比由0.15提高至1.21;生长的Y³⁺/Li⁺及Y³⁺/Na⁺共掺杂BaF₂晶体的慢发光成分较Y³⁺掺杂BaF₂晶体进一步降低,快/慢成分比最高分别可达1.63和1.61。研制的双掺杂BaF₂快响应闪烁晶体有望应用于高能物理、核物理前沿实验等重要领域。     

PbWO4:(Sb,Y)晶体的发光和闪烁性能研究

本文报道了用多坩埚下降法生长的大尺寸PbWO4:(Sb,Y)晶体的光谱和闪烁性能.基于透射光谱、X射线激发的发射谱、紫外激发及其发射谱、光产额和超短脉冲X射线激发荧光寿命等方面的测试,讨论了Sb,Y双掺杂对PbWO4晶体的光谱和闪烁性能的作用.结果表明:Sb,Y双掺杂能显著改善PbWO4晶体的光谱性能和闪烁性能,使PbWO4晶体在短波方向的透过率明显提高;对于尺寸为23×23×20mm3的掺杂晶体样品,光产额最大值大约为50 p.e./MeV,约为BGO光产额的6.0;;发光成份中有1.9ns和15.8ns两个衰减时间常数的快成份.     

Luminescent properties of CsI single crystals grown from the melt treated with EuI2

CsI single crystals treated with EuI₂ as a scavenger are grown and their radioluminescence spectra and scintillation light decay curves are obtained. Addition of the quantities of the scavenger comparable with the total concentration of the oxygen‐containing admixtures in the melt results in complete destruction of the latter. In its turn, this causes the disappearance of the band with a maximum at 2.8 eV in the radioluminescence spectrum and decreases the fraction of the slow 2 µs‐component to 0.01. The addition of larger quantities of EuI₂ leads to the appearance of a wide band with the maximum at 2.8 eV characterized by a decay constant of 2 µs; its intensity increases with the EuI₂ concentration. The maximum ratio of two faster components with the decay constants equal to 7 and 30 ns approaches 0.58:0.41 at EuI₂ concentration in CsI melt equal to 0.01 mol·kg⁻¹.     

Photoluminescence and microstructure of Mn-doped ZnS phosphor powder co-fired with ZnS nanocrystallites

In this study, we correlated the photoluminescence (PL) with the microstructure of ZnS:Mn phosphor powders prepared by firing ZnS with MnO (1 mol%), NaCl (1 mol%) and ZnS nanocrystallites (NCs) in the range of 0–100 wt% at 600–1000 °C for 2 h in the atmosphere of 3%H₂/Ar. ZnS NCs of 10–30 nm in size were produced by co-precipitation of zinc nitrate and sodium sulfide solutions at room temperature. Thermal analysis (DTA/TG) and X-ray diffraction (XRD) results indicated that the cubic-hexagonal transformation temperature of ZnS NCs was lowered to approximately 600 °C, which was much lower than that of bulk ZnS (1020 °C). PL measurements revealed that ZnS:Mn fired with 1 wt% ZnS NCs showed the optimal luminescence intensity when compared to those without or with higher ZnS NCs (>1 wt%). An appropriate amount of ZnS NCs (1 wt%) acting as the flux in the firing process was inferred to avoid the inhomogeneous distribution of Mn²⁺ as well as the migration of excitation energy to quenching sites and therefore to result in the enhanced PL intensity.     

Structural,optical and photoluminescence properties of ZnS: Cu nanoparticle thin films as a function of dopant concentration and quantum confinement effect

Thin films of ZnS: Cu nanoparticles were deposited in chemical bath by a pH controlled solution synthesis technique. The copper concentration was varied from 0 to 0.1M%. XRD and SEM indicated variations in diffracted intensity and morphology with Cu concentration. The PL spectrum of the undoped ZnS nanoparticles showed emission peaks at 393 and 432nm that could be attributed to the intrinsic defect states of ZnS nanoparticles. For ZnS: Cu samples three peaks in the range of 390nm, 480nm and 525nm were observed. With increase in Cu concentration from 0.001 to 0.1M%, the peak position of 480nm and 525nm did not change, whereas 390nm peak red shifted to longer wavelength region to 422nm. In addition, it was found that the overall photoluminescence intensity reached maximum at 0.01M% and quenched with further increase in Cu concentration. Enhancement of blue and green light emission by seven and twenty fivefold respectively compared to undoped ZnS was observed in ZnS: Cu with optimal dopant concentration. Time resolved decay of photoluminescence showed faster decay for 390 – 420nm purple/ blue emission compared to green (525nm) Cu related emission which is in the microsecond time scale. Optical absorption measurements indicate enhancement of band gap (3.89eV) for undoped ZnS suggesting the quantum confinement effect in the developed nanoparticles of size below the Bohr diameter. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

掺杂抑制氟化钡晶体慢闪烁成分研究进展

高能物理强度前沿装置、飞行时间技术正电子发射断层扫描、超高频辐射成像和正电子湮灭寿命谱分析等应用对闪烁体的时间响应提出了更高的要求,发展超快衰减闪烁体已成为研究热点之一。氟化钡晶体是一种具有亚纳秒级快闪烁成分的独特无机闪烁体,但其衰减时间约0.6 μs的慢闪烁发光成分会在高计数率应用时引起严重的信号堆积。作为一种抑制慢闪烁成分的有效途径,氟化钡晶体慢闪烁成分抑制的掺杂研究在过去三十年受到持续关注。本文回顾了掺杂抑制氟化钡晶体慢闪烁成分的研究历史,提出了掺杂元素选择的基本原则,重点介绍稀土金属(La、Y、Lu和Sc)、碱土金属(Mg、Sr)、过渡金属(Cd)和碱金属(K)等掺杂的慢闪烁成分抑制特性、内在机理和应用研究情况,并展望了所面临的挑战与机遇。     

Kinetics of luminescence of CsI single crystals scavenged by Y3+

CsI single crystals were grown from the melt scavenged by Y³⁺ (YCl₃) addition in 6.7·10⁻⁴–6.7·10⁻³ mol·kg⁻¹ range. The addition of the scavenger amounts comparable with the total concentration of the oxygen‐containing admixtures in molten CsI results in complete destruction of the latter. Because of this, the intensity of the band with a maximum at 2.8 eV in radioluminescence spectra caused by the oxygen‐containing admixtures (anion vacancies) considerably decreases, and the fraction of the slow 2μs‐component corresponding to these admixtures becomes lower than 0.01 (0.007). The addition of larger quantities of YCl₃ leads to the appearance of a wide band with a maximum at 2.8 eV caused by cation vacancies, and the intensity of the slow 2μs‐component increases to 0.02. The maximum ratio of two faster components with the decay constants equal to 7 and 30 ns reaches 0.65:0.33 at Y³⁺ concentration in CsI melt equal to 6.7·10^‐3 mol·kg^‐1, the effective luminescence time of fastest components is ca 14 ns. The dependence of the ‘Fast/Total ratio’ on Y³⁺ concentration passes through its maximum (0.81) corresponding to the equivalence of Y³⁺ and O²⁻ concentrations in the growth CsI melt.     

利用皮秒激光激发技术研究纳米硫增感溴化银中光电子特性

纳米硫增感作为一种新型的增感手段,能很大程度上提高卤化银感光材料的性能.卤化银中光电子信号十分微弱,光电子寿命在纳秒量级,本文采用微弱信号的微波吸收相敏检测技术,它能精确地测量载流子的时间特性,反映感光过程的细微变化.通过测量我们获得了不同纳米硫化物粒子增感的立方体溴化银乳剂中光电子的瞬态行为,分析了不同增感温度对增感的溴化银乳剂中光生电子随增感时间而衰减的影响.结果表明:当增感温度增加时,可以缩短乳剂达到最佳光电子利用率的增感时间.