共查询到20条相似文献,搜索用时 250 毫秒
1.
稀土固体是重要的激光和光电子材料。目前 ,由于以宽带信号和太赫兹比特数据传输率为特征的信息技术的发展 ,稀土固体材料的相干瞬态动力学过程成为宽带与高速信息光子学的基本物理问题之一。研究了室温下稀土粉末样品Eu3+ ∶Y2 O3自由感应衰减的相干瞬态光谱 ,这有助于理解有效的光吸收动力学、激发态弛豫、相干能量传递和超短光脉冲在稀土固体中的传播。用一对紫外飞秒相干光脉冲作用于稀土粉末样品Eu3+ ∶Y2 O3,然后监测物质激发态的布居数随两个激发脉冲之间的延时的变化 ,测量到其自由感应衰减量子拍 (FID) ,从拍频周期分析确定了其能级精细结构 ,能级的退相时间长达皮秒量级。理论分析和实验结果符合得很好。对稀土离子的量子干涉的研究 ,表明其在受激受控光放大方面具有潜在的应用前景 相似文献
2.
3.
用共沉淀法制备了Y2O2S:Eu3+,Mg2+,Ti4+红色长余辉材料。测量了材料的电子显微形貌、晶体结构和发射光谱。通过与固相法制备的Y2O2S:Eu3+,Mg2+,Ti4+长余辉材料比较,发现两种方法都可以制备粒度基本相同的纯相Y2O2S基质晶体,但共沉淀法样品的颗粒结构更松散。研究了Eu3+浓度对两种方法制备样品的谱线发射强度的影响,通过比较共沉淀法和高温固相法制备的样品中Eu3+的5D1→7F3较高能级跃迁的587.6nm谱线强度随Eu3+浓度的变化,发现共沉淀法更有利于Eu3+均匀进入Y2O2S基质晶格而形成有效的发光中心。 相似文献
4.
5.
6.
采用溶胶-凝胶法在还原气氛下制备了Sr2MgSi2O7∶Eu2+,xBi3+(x=0,0.02,0.04,0.06,0.08,0.1)荧光粉,并用XRD、TG-DTA及激发与发射谱仪对样品的结构及发光性能进行了表征。结果发现:单掺杂Bi3+的Sr2MgSi2O7样品的发射光谱所用的材料的激发光谱为一主峰为286 nm的宽带谱,这是由于激发态时Bi3+的3P1→1S0电子能级跃迁而造成的;单掺杂Eu2+的Sr2MgSi2O7样品的发射光谱所用的材料的激发光谱为一主峰为358 nm的宽带谱,这是典型的Eu2+的4f65d1→4f7跃迁而引起的。当Bi3+离子掺杂到Sr2MgSi2O7∶Eu2+样品的摩尔分数为0.04时,样品的发射强度是未掺杂Bi3+离子样品的1.9倍。 相似文献
7.
Eu3+或Tb3+掺杂Y2O3纳米材料紫外激发光谱 总被引:2,自引:0,他引:2
采用燃烧法制备了不同Ln3+(Ln=Eu或Tb)掺杂浓度和不同平均粒径的Y2O3:Ln纳米晶体粉末和体材料样品。研究发现随着粒径的减小,Y2O3:Eu电荷迁移带的位置发生红移;并且,由于存在于近表面低结晶度环境中的Eu3+数量的增加,小粒径样品(5nm)的电荷迁移带还向长波方向发生了明显的展宽。实验中还观察到Y2O3:Tb纳米晶激发谱中4f5d(4f8→4f75d1)跃迁吸收对应激发峰(带)的谱线形状随样品粒径变化存在较大的差异,这是由于Tb3+存在于近表面的低结晶度和颗粒内部的高结晶度两种不同环境中,Tb3+的4f5d跃迁在两种环境中对应的吸收峰位置不同,当样品粒径发生变化时Tb3+处于两种环境中的比例随之变化,造成相应吸收跃迁对应的激发峰(带)强度发生变化,并改变了激发谱的谱线形状。实验中还发现,随着Tb3+(或Eu3+)浓度的减小,Y2O3基质激子跃迁吸收的激发峰对比4f5d跃迁(或电荷迁移带)激发峰的相对强度随之增强。 相似文献
8.
非晶纳米发光材料(Y,Eu)2O3-SiO2发射光谱的分析研究 总被引:1,自引:1,他引:0
EXAFS测定表明sol-gel方法制备的纳米非晶(Y,Eu)2O3-SiO2发光材料中,发光中心Eu3+的局域环境和晶态X2型Y2SiO5Eu中Eu3+离子的局域环境相似。以此结构为依据,用M. F. Reid的方案计算了晶场迭加模型中的能级参数及光谱强度参数,并得到了与实验结果基本一致的理论光谱图. 相似文献
9.
采用高温固相法合成出La2Mo2O9:Eu3+,W6+系列红色荧光粉,其结构为立方晶系的β- La2Mo2O9。在395 nm光激发下,样品La1.40Mo2O9:0.60Eu3+发射出很强的红光,最强发射峰位于616 nm处。适量地掺杂W6+离子可以提高样品的激发和发射强度,在395 nm光激发下,La1.40Mo1.84O9:0.60Eu3+,0.16W6+荧光粉的Eu3+的5D0→7F2跃迁发射强度最大,是样品La1.40Mo2O9:0.60Eu3+的1.23倍。最后,将La1.40Eu0.60Mo1.84O9:0.16W6+荧光粉与~395 nm发射的InGaN芯片一起制作成红光发光二极管(LED),该LED发射出很强的红光。 相似文献
10.
采用固相反应法合成了组成为Ca1-xEuxSi2O2N2的Eu2+掺杂CaSi2O2N2荧光粉.通过荧光光谱对样品的发光性能进行了研究,发现Eu2+掺杂CaSi2O2N2荧光粉发射光谱为宽波段的单峰结构,主要包含绿光和黄光区,发射峰在556~568 nm.从发射光谱的宽带特征来看,CaSi2O2N2:Eu2+的发射主要对应着Eu2+离子4f65d→4f7跃迁.从激发光谱所覆盖的范围还可以看到,样品可以有效的被UV蓝-光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用.另外,样品的发光性能与激发离子的浓度有着很大关系.激发离子浓度增大时,发射光谱会发生明显红移.利用这一性质,可以通过改变Eu2+浓度来调节荧光粉的发光范围,从而满足不同场合的需要.同时,Eu2+浓度提高,样品发射光谱的强度也会随之增强,在x=0.06时发射强度达到最大值,之后继续增加Eu2+浓度,强度不仅没有增加反而降低,即出现浓度猝灭现象. 相似文献
11.
稀土是重要的战略物资资源,有一些已形成产业,在永磁、发光、催化和储氢等方面有着重要的作用. 对稀土及其化合物的研究一直是国内外研究的热点.对稀土原子结构和价电子结构的研究有助于对其的更深刻的理解. 依据固体与分子经验电子理论,对镧系稀土和Sc, Y的价电子结构进行系统地研究, 并以此为基础,对它们的熔点和结合能做进一步分析,分析结果和实验值相符. 研究结果表明:稀土金属的结构与晶格电子和共价电子密切相关,随着晶格电子向共价电子的转换, 稀土金属的熔点趋于增加.稀土的价态变化也是影响电子分布和性能的主因, 如: Sm和Eu的熔点与电子结构的关系不同于其他稀土,外壳层的共价电子之间的转化是其熔点与其他元素之间差别较大的主要原因.稀土的4f电子对结合能的影响大,这是源于其4f电子引发的收缩效应. 此结果揭示了决定稀土熔点和结合能的主要因素是稀土的价电子结构的变化. 相似文献
12.
13.
14.
合成了邻菲罗啉(phen)衍生物2-苯基-咪唑并 -1,10-菲罗啉(PIP),并以其为第二配体,苯甲酸(BA)为第一配体,制备出新型稀土铕三元有机配合物Eu(BA)3PIP;在相同条件下,第一配体不变,1,10-菲罗啉为第二配体,还制备出Eu(BA)3phen。采用元素分析、红外光谱、热重和差热分析等技术对合成的配体PIP及配合物Eu(BA)3PIP和Eu(BA)3phen进行了表征。通过发光光谱研究了配合物的发光性质,结果表明第二配体PIP有较大的共轭体系,在紫外光激发下,配合物中的配体可将吸收的能量传递给稀土Eu3+离子,表现出较强的Eu3+离子的特征发射。两种配合物相比,Eu(BA)3PIP的发光强度明显大于Eu(BA)3phen的发光强度,说明适宜的第二配体对配合物有很好的敏化发光作用。 相似文献
15.
Correlation between valence electronic structure and magnetic properties in RCo_5(R=rare earth) intermetallic compound 下载免费PDF全文
《中国物理 B》2016,(6)
The magnetisms of RCo_5(R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules(EET).The theoretical moments and Curie temperatures agree well with experimental ones.The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo_5 intermetallic compounds.The moments of RCo_5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth,and the s electrons also affect the magnetic moments by the hybridization of d and s electrons.It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons.In the heavy rare-earth-based RCo_5 intermetallics,the contribution to magnetic moment originates from the 3d and 4f electrons.The covalence electrons and lattice electrons also affect the Curie temperature,which is proportional to the average moment along the various bonds. 相似文献
16.
为了研究稀土掺杂对单层MoS2电子结构的影响,文章基于密度泛函理论框架下的第一性原理,采用平面波赝势方法分别计算了本征及La,Ce,Nd掺杂单层MoS2的晶格参数、能带结构、态密度和差分电荷密度.计算发现,稀土掺杂所引起的晶格畸变与杂质原子的共价半径大小有关,La杂质附近的键长变化最大,Nd杂质附近的键长变化最小.能带结构分析表明,La掺杂可以在MoS2的禁带中引入3个能级,Ce掺杂可以形成6个新能级,Nd掺杂可以形成4个能级,并对杂质能级属性进行了初步分析.差分电荷密度分布显示,稀土掺杂可以使单层MoS2中的电子分布发生改变,尤其是f电子的存在会使差分电荷密度呈现出反差极大的物理图象. 相似文献
17.
Elementary scattering processes in solid matter occur on ultrafast timescales and photoelectron spectroscopy in the time domain represents an excellent tool for their analysis. Conventional photoemission accesses binding energies of electronic states and their momentum dispersion. The use of femtosecond laser pulses in pump‐probe experiments allows obtaining direct insights to the energy and momentum dependence of ultrafast dynamics. This article introduces the elementary interaction processes and emphasizes recent work performed in this rapidly developing field. Decay processes in the low excitation limit are addressed, where electrons decay according to their interaction with carriers in equilibrium. Here, hot electron relaxation in epitaxial metallic film is reviewed. In the limit of an intense optical excitation, scattering of the excited electrons among each other establishes a non‐equilibrium state. Results on charge‐density wave materials and the effect of coherent nuclear motion on the electronic structure, which can break low symmetry ground states, are discussed. Figure reprinted with permission from [71]. 相似文献
18.
Resonance fluorescence of gamma radiation under conditions of coherent mixing of Mössbauer sublevels
A method is proposed for calculating the resonance fluorescence spectrum of coherent gamma radiation with a finite linewidth under conditions when the sublevels of the ground nuclear state are coupled through a strong field. The spectrum line shape is substantially affected by both the coherent effects induced in the system by a strong field and the finite gamma-radiation width. The results obtained earlier and in this work give impetus to experimental investigations into the coherence of a quantum system and quantum interference of Mössbauer gamma transitions through the excitation of coherent magnetization dynamics or an optical subsystem in solids. 相似文献
19.
H. Schneider C. Schnbein K. Schwarz M. Walther 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
We have studied the transport properties of electrons in asymmetric quantum well structures upon far-infrared optical excitation of carriers from the lowest subband into the continuum. Here the photocurrent consists of a coherent component originating from ballistic transport upon excitation, and of an incoherent part associated with asymmetric diffusion and relaxation processes, which occur after the coherence has been lost. The signature of the coherent contribution is provided by a sign reversal of the photocurrent upon changing the excitation energy. This sign reversal arises from the energy-dependent interference between continuum states, which have a twofold degeneracy characterized by positive and negative momenta. The interference effect also allows us to estimate the coherent mean free path (
nm at 77
K). In specifically designed device structures, we use both the coherent and incoherent components in order to achieve a pronounced photovoltaic infrared response for detector applications. 相似文献
20.
G.V. Subba Rao B.M. WanklynC.N.R. Rao 《Journal of Physics and Chemistry of Solids》1971,32(2):345-358
Rare earth ortho-chromites, -manganites and -ferrites are p-type semiconductors with conductivities in the range 10−4–10−1 ohm−1 cm−1. The conductivity in each series of perovskites decreases with the increasing atomic number of the rare earth. The ionic contribution to conductivity is small in all the three series of solids. None of these solids exhibits intrinsic behavior up to ∼1000°C. The conductivity behaviors of these rare earth compounds reflect the known crystallographic, dielectric and magnetic transitions in these materials. Seebeck coefficients in these compounds are large, typical of narrow-band materials; the Seebeck coefficients show marked changes at temperatures where magnetic and dielectric transitions occur. The electrical transport properties of all the three series of rare earth compounds are essentially controlled by the d-electrons of the transition elements which show localized behavior. This conclusion is in agreement with the results from optical spectra and the predictions of Goodenough. In all these compounds small polarons seem to be responsible for the conduction. 相似文献