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1.
Cu K-edge and La L3-edge X-ray absorption spectra have been measured on a series of nominal LaxxCuO4 samples with x≤2.00. The extended X-ray absorption fine structure (EXAFS) results show that the x<2.0 samples always consist of stoichiometric (La/Cu=2/1) La2CuO4 and CuO. The number of La vacancies in the La2CuO4 structure, if any, should be very small. The sensitivity of the EXAFS technique to impurity phases under favorable conditions is demonstrated.  相似文献   

2.
佟建波  黄茜  张晓丹  张存善  赵颖 《物理学报》2012,61(4):47801-047801
本文采用共烧结工艺将纳米Ag颗粒引入Yb3+, Er3+共掺的NaYF4上转换材料中, 利用X射线衍射及扫描电子显微镜技术对制备的NaYF4材料进行结构特性和表面形貌的表征, 通过吸收谱及荧光光谱测试技术对NaYF4材料光吸收及光发射特性进行表征. 通过对纳米Ag颗粒引入量的优化, 获得了Yb3+, Er3+共掺的NaYF4上转换材料荧光发射峰的增强, 300—800 nm全光谱范围内增益达28%, 在544 nm处获得最大增益55%, 具有显著的荧光增强效果. 同时分析了不同数量纳米Ag颗粒的引入对NaYF4材料吸收谱及光致发光特性影响, 指出了表面等离子激元的光猝灭及共振吸收增强作用机理.  相似文献   

3.
4.
Data are presented on the relative photon yield of Lu2SiO5(Ce3+), Cd2SiO5(Ce3+), CdWO4, BaF2, YAlO3(Ce3+) and Lu3Al5O12(Sc3+) scintillation of crystals on absorption of X-ray and γ-ray photons at energies ranging from 5 keV to beyond 1 MeV.  相似文献   

5.
姜平国  汪正兵  闫永播  刘文杰 《物理学报》2017,66(24):246801-246801
采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了W_(20)O_(58)晶胞、W_(20)O_(58)(010)表面结构及其氢吸附机理.计算结果表明:W_(20)O_(58)晶体理论带隙宽度为0.8 eV,为间接带隙,具有金属性.W_(20)O_(58)晶体中W—O共振较强,以共价键居多.W_(20)O_(58)(010)表面有WO终止(010)表面和O终止(010)表面,表面结构优化后使得W—O键长和W—O—W键角改变,从而实现表面弛豫.分别计算了H_2分子吸附在WO终止(001)表面和O终止(001)表面的WO-L-O_(1c),WO-V-O_(1c),WO-L-O_(2c),WO-V-O_(2c),O-L-O_(1c)和O-V-O_(1c)六种吸附构型,其中WO-L-O_(1c),WO-V-O_(1c)和WO-L-O_(2c)这三种吸附构型不稳定;而WO-V-O_(2c),O-L-O_(1c)和O-V-O_(1c)这三种吸附构型都很稳定,H_2分子都解离成两个H原子,吸附能均为负值,分别为-1.164,-1.021和-3.11 eV.WO-V-O_(2c)吸附构型的两个H原子分别吸附在O和W原子上;O-L-O_(1c)吸附构型的两个H原子,一个与O原子成键,另一个远离了表面.其中O-V-O_(1c)吸附构型最稳定,两个H原子失去电子,为O原子提供电子.分析其吸附前后的态密度,H的1s轨道电子与O的2p,2s轨道电子相互作用,均形成了一些较强的成键电子峰,两个H原子分别与O_(1c)形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.  相似文献   

6.
We report here on an X-ray absorption study of La0.7Sr0.3MnO3 films epitaxially grown on SrTiO3 substrate. The local organization around Mn in oriented films with 600 Å in thickness was investigated by polarized Extended X-ray Absorption Fine Structure. The angle between electric field vector and film surface was set equal to 5° and 70° to investigate almost independently the contribution of the manganese neighbors situated in and out of the film plane. The first neighboring shell oxygen is found to be the same in both geometries, but small changes in the next neighboring contribution are observed. These changes are associated with variation in the Mn–Mn bond length. A small in-plane elongation (3%) is observed in the constrained films with respect to the unconstrained case.  相似文献   

7.
Well-crystallized Ba0.5Sr0.5TiO3 thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10−3 Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba0.5Sr0.5TiO3 rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba0.5Sr0.5TiO3 thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n2 = 5.04 × 10−6 cm2/kW and β = 3.59 × 10−6 (m/W), respectively.  相似文献   

8.
We report on the BCC to FCC/HCP structural transformation of Co70Fe30 alloy produced by room temperature ion irradiation of Co70Fe30/Cu discontinuous multilayers. The structural changes were analyzed by X-ray diffraction and X-ray absorption spectroscopy. For this study, two different samples were examined, one irradiated with 50 keV He+ and another with 600 keV Kr+ with doses of 1×1017 and 3×1015 ions/cm2, respectively. No substantial change is observed after He+ irradiation, while after Kr+ irradiation an unexpected structural transition from BCC to FCC/HCP closed packed of the Co70Fe30 alloy was found.  相似文献   

9.
The structure and NO reactivity of Zr-deposited Pd surfaces were investigated by X-ray photoelectron spectroscopy, low-energy electron diffraction, infrared reflection absorption spectroscopy, and temperature-programmed desorption. Zr on Pd(1 0 0) was oxidized to ZrO2 by exposure to O2 at 773 K. Heating at 823 K in a vacuum led to decomposition of ZrO2 to Zr metal and O2. The activation energy for ZrO2 decomposition changed remarkably at ΘZr = 0.4. For ΘZr > 0.4, a hexagonal structure was observed for ZrO2/Pd(1 0 0); no ordered structure was observed for ΘZr < 0.4. Deposited Zr had no significant effect on the adsorption and decomposition of NO on Pd(1 0 0) but resulted in a creation of new NO dissociation sites on Pd(3 1 1). Zr on Pd(3 1 1) was oxidized to ZrOX by oxygen produced from NO dissociation. Heating at 823 K in a vacuum led to decomposition of ZrOX to Zr metal and O2.  相似文献   

10.
贺江凡  舒庆 《发光学报》2019,40(5):595-601
采用溶胶-凝胶法合成了Sr_3MgSi_2O_8∶Eu~(3+)红色荧光粉,并通过X射线衍射(XRD)、傅立叶变换红外光谱(FTIR)、扫描电镜(SEM)以及荧光光谱(PL)、X射线光电子能谱(XPS)等分析方法,对不同烧结温度(950,1 050,1 150,1 250℃)热处理4 h后得到的粉体的物相、形貌及发光性能进行了表征分析。由XRD表征结果可知,制备出的样品为正交晶系的Sr_3MgSi_2O_8;由扫描电镜及比表面积的测试结果可知,经过1 150℃热处理得到的荧光粉具有最大比表面积,可达到90.213 1 m~2/g,且粒径大小均一;由红外光谱图可知:样品中含有Si—O—Si、Mg—O和Sr—O化学键;在394 nm的激发波长下,所有样品在614 nm和702 nm处出现了强发射峰,分别对应于Eu~(3+)的~5D_0→~7F_2和~5D_0→~7F_4跃迁,属红光发射。随着热处理温度的升高,样品所对应的发射峰强度呈现出先增大后减小的变化趋势,即出现温度猝灭效应;经1 150℃热处理合成的Sr_3MgSi_2O_8∶Eu~(3+)红色荧光粉的发光性能最好,即最佳的热处理温度为1 150℃。  相似文献   

11.
Absorption, emission and excitation spectra of CaF2, SrF2, BaF2 crystals doped by Y bF3 or EuF3 impurities were studied in 1–12 eV spectral region. The intensive absorption broad bands (denoted as CT1) were observed in all cases just below the 4f–5d absorption region. Less intensive absorption bands, denoted as CT2, having energies 1.2–1.5 eV lower than those of CT1, were observed in CaF2, SrF2 crystals doped by EuF3 or Y bF3 impurities.

High resolution emission spectra of Eu-doped CaF2 and SrF2 crystals excited into CT1 and CT2 bands were measured. Under excitation into CT1 bands, all present Eu sites (C4v, Oh and some aggregates) were observed in emission spectra. While under excitation into CT2 bands, only the emission of C4v sites was observed.  相似文献   


12.
王凯  张文华  刘凌云  徐法强 《物理学报》2016,65(8):88101-088101
VO2表面氧缺陷的存在对VO2材料具有显著的电子掺杂效应, 极大地影响材料的本征电子结构和相变性质. 通过2, 3, 5, 6-四氟-7, 7', 8, 8'-四氰二甲基对苯醌(F4TCNQ)分子表面吸附反应, 可以有效消除表面氧缺陷及其电子掺杂效应. 利用同步辐射光电子能谱和X射线吸收谱原位研究了修复过程中电子结构的变化以及界面的化学反应, 发现这种方式使得VO2薄膜样品氩刻后得到的V3+失去电子成功地被氧化成原先的V4+, 同时F4TCNQ分子吸附引起电子由衬底向分子层转移, 界面形成带负电荷的分子离子物种. 受电化学性质的制约, F4TCNQ分子吸附反应修复氧缺陷较氧气氛退火更安全有效, 不会引起表面过度氧化形成V2O5.  相似文献   

13.
Shaped single crystals of (LuxGd1−x)3Ga5O12 (0.0x1.0) and (Yb0.05LuxGd0.95−x)3Ga5O12 (0.0x0.9) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)3Ga5O12 are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd3+ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd3+ or Yb3+ cations below 240 nm. A complete absence of Yb3+ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb3+ by that of Gd3+ ions. For specific composition of Lu1.5Gd1.5Ga5O12 an intense defect-host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi4Ge3O12, was found.  相似文献   

14.
赵湘辉  魏爱香  招瑜 《发光学报》2011,32(8):793-797
采用化学水浴以CdCl2·H2O、CS( NH2)2、NH4Cl、NH3·H2O和去离子水作为反应前驱物制备CdS纳米晶薄膜.采用扫描电镜( SEM)、X射线衍射(XRD)、透射光谱和稳态荧光光谱,研究了反应前驱物中不同的n(S)∶n(Cd)对所制备的CdS薄膜的形貌、结构和光学性能的影响.结果表明:反应前驱物中n(S...  相似文献   

15.
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       下载免费PDF全文
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   

16.
The positions and intensities of all vibrational transitions in the (ν1, 2ν2) Fermi doublet region of (CO2)2 dimers are obtained by means of variational method. The collision-induced absorption in compressed carbon dioxide is shown to be mainly due to dimeric absorption. Assignment of ν1 and 2ν2 vibrational bands in isolated CO2 molecule is performed by consideration of the symmetries and intensities of dimeric vibrations.  相似文献   

17.
Here we present the characteristic signatures in X-ray absorption and photoemission spectroscopy for molecular damage in adsorbed monolayers of bi-isonicotinic acid on a rutile TiO2(1 1 0) surface. Bi-isonicotinic acid is the anchor ligand through which many important inorganic complexes are bound to the surface of TiO2 in dye-sensitized solar cells. The nature of the damage caused by excessive heating of the adsorbed monolayer is consistent with splitting the molecule into two adsorbed isonicotinic acid molecular fragments. The effect on the lowest unoccupied molecular orbitals (involved in electron transfer in the molecule) can be understood in terms of the adsorption geometry of the reaction products and their nearest neighbor interactions.  相似文献   

18.
High quality gallium nitride thin films have been successfully grown on the Ga-diffused Si(1 1 1) substrates through ammoniating Ga2O3 thin films deposited by r.f. magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscope (AFM) and photoluminescence (PL) were used to characterize the synthesized samples. The analyses reveal that the formed films are high quality polycrystalline hexagonal gallium nitride. The as-formed GaN films show a flat surface topography with RMS roughness varied from 29 to 48 Å. The strong near-band-edge-emission peak around 368 nm was observed at room temperature. This is a novel method to fabricate GaN thin films based on the direct reaction between Ga2O3 and NH3 on the Ga-diffused Si(1 1 1) substrates.  相似文献   

19.
王谦  刘卫国  巩蕾  王利国  李亚清 《物理学报》2018,67(21):217201-217201
提出了采用双波长自由载流子吸收技术同时测量半导体材料载流子体寿命和前表面复合速率的方法.通过数值模拟,定性分析了不同载流子体寿命和前表面复合速率对信号的影响,同时对测量参数的可接受范围和不确定度进行计算并与传统频率扫描自由载流子吸收方法测量结果进行比较.结果表明:提出的双波长自由载流子吸收方法可明显减小载流子体寿命和前表面复合速率的测量不确定度,提高参数测量精度;表面杂质和缺陷越多的样品,其前表面复合速率测量不确定度越小.进一步分析表明,此现象与不同波长激光抽运产生的过剩载流子浓度分布不同有关.  相似文献   

20.
采用水热-焙烧法制备了Ce掺杂的可见光响应的Bi2O3光催化剂(Ce-Bi2O3)。利用 XRD、FT-IR、XPS和 UV-Vis对不同Ce-Bi2O3样品进行了表征分析,并以光催化降解金橙Ⅱ溶液为探针反应,考察了Ce-Bi2O3的可见光催化性能。结果表明,Ce掺杂可以减小催化剂的禁带宽度,使光谱响应范围向可见光拓展。掺杂的Ce可取代Bi2O3晶格中部分Bi,形成Bi-O-Ce键,并生成了少量铈铋复合氧化物(Bi7.38Ce0.62O12.31),它们的存在有效地抑制了光生电子-空穴对的复合,有助于提高Bi2O3的可见光催化活性。但焙烧时间过长将导致Ce-Bi2O3催化剂的表面发生烧结现象,致使其催化活性降低。可见光照射下的金橙Ⅱ光催化降解实验表明,经2 h焙烧后得到的Ce/Bi的量比为0.5 的Ce-Bi2O3催化剂具有最佳的光催化活性。  相似文献   

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