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1.
2.
The thermally stimulated properties of PbWO4 in the temperature range 90–400 K have been investigated on undoped and terbium-doped crystals after X-ray irradiation at 90 K. Doping with terbium changes the concentration of shallow traps, which are responsible for retrapping free electrons and holes. Light illumination can change the distribution of the traps. The optically stimulated luminescence is observed. The influence of light illumination on the TSL curves and emission properties is studied. The possible mechanism of TSL phototransformation is discussed. 相似文献
3.
V.M. Khulugurov V.N. Salomatov I.M. Kalogeras A. Vassilikou-Dova I. Christakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):91-101
Thermally Stimulated Depolarisation Current (TSDC) and optical methods are applied to a range of alkali-fluoride crystals
in order to establish a model for the stable F
2
+
- like colour centres in LiF:OH-. The experimental results for LiF:OH- suggest that the OH- defects are partially destroyed under ionising irradiation or during crystal growth. The low-temperature dielectric relaxation
signals in LiF:OH- and LiF:Mg2+,OH- are attributed to highly interacting hydroxide ions and products of their destruction located in extended lattice defects.
In LiF:OH-, in contrast to other alkali halides, the results advocate for a defect-structure model, which considers a neutral defect
(ND, probably O2 or H2) sited at the anion vacancy of the O2--V
a
+
dipole and which possibly is the “nucleus” for the F
2
+
centre. The proposed F
2
+
(ND, O-) model seems to better explain the dielectric results, compared to the older F
2
+
(O2-) and F
2
+
(O-) models. The estimate for the electric dipole moment derived from the experimental TSDC bands, gives a value for the F
2
+
- like centre in LiF:OH- between those of the F
2
+
(O-) and F
2
+
(O2-) defects, in good agreement with the proposed F
2
+
(ND,O-) model. The reduction of the activation energy barrier of the (re)orientation process of the Mg2+V
c
-
(OH-) complexes in LiF:Mg2+,OH-, and the low-temperature shift of their TSDC band, compared to the single Mg
2
+
V
c
-
peak in LiF:Mg2+, are tentatively ascribed to an increase in the crystal-lattice parameters owing to the presence of OH- and/or products of its destruction.
Received 31 August 2001 / Received in final form 30 March 2002 Published online 9 July 2002 相似文献
4.
以巯基丙酸(MPA)为稳定剂, 利用共沉淀法制备了水溶性的Ag掺杂的ZnxCd1-xS合金型纳米晶. Ag掺杂后ZnxCd1-xS纳米晶产生新的发射峰, 并且发光效率得到了有效提高. 通过改变纳米粒子中Zn/Cd比例可有效地调控ZnxCd1-xS∶Ag纳米晶的吸收带隙宽度, 同时可以在425~603 nm之间实现对ZnxCd1-xS∶Ag纳米晶发射峰位的连续调控. 相似文献
5.
以巯基丙酸(MPA)为稳定剂, 利用微波辐射加热方法制备了水溶性的Cu掺杂的ZnS纳米晶. 通过改变微波条件, 可以在460~572 nm之间实现对ZnS∶Cu纳米晶发射峰位的连续调控. 通过XRD、 UV-Vis、荧光及荧光衰减对ZnS∶Cu纳米晶的结构和发光性质进行了详细探索, 并利用时间分辨荧光光谱对其发光机理进行了初步研究. 相似文献
6.
STUDY ON 1-HEXENE POLYMERIZATION BASED ON ZIEGLER-NATTA CATALYSTS WITH DOPED SUPPORT 总被引:1,自引:0,他引:1
XueJiang Zhi-qiangFan 《高分子科学》2004,(4):305-308
A series of Ti/Mg supported catalysts are prepared by using ball-milled mixtures of MgCl2-ethanol adducts and NaCl as supports, and 1-hexene polymerizations catalyzed by the novel catalysts are studied. It is found that the molecular weight distribution of poly(1-hexene) becomes apparently narrower when catalysts with doped supports are used, indicating that changing the structure of the support is an effective way to regulate the active center distribution of heterogeneous Ziegler-Natta catalyst. 相似文献
7.
Jihong Cheng 《Journal of solid state chemistry》2004,177(1):126-133
LaGaO3 perovskites doped with Sr or Ba at the La site and Mg at the Ga site were prepared by solid-state reaction or sol-gel method and characterized. Enthalpies of formation from constituent oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. Energetic trends are discussed in terms of defect chemistry. As oxygen deficiency increases, formation enthalpies define three trends, LaGa1−yMgyO3−δ (LGM), La1−xSrxGa1−yMgyO3−δ (LSGM), and La1−xBaxGa1−yMgyO3−δ (LBGM). They become less exothermic with increasing doping, suggesting a dominant destabilization effect from oxygen vacancies. The endothermic enthalpy of vacancy formation is 275±37, 166±18 and 138±12 kJ/mol of VO·· for LGM, LBGM and LSGM, respectively. Tolerance factor and ion size mismatch also affect enthalpies. In terms of energetics, Sr is the best dopant for the La site and Mg for the Ga site, supporting earlier studies, including oxygen ion conductivity and computer modeling. 相似文献
8.
掺杂阴离子对电化学合成的聚邻甲苯胺性质的影响 总被引:3,自引:0,他引:3
邻甲苯胺在酸性介质中的聚合速率与酸的种类有关,聚合速率影响了各种掺杂阴离子聚合物膜的形态,聚合物的电导率、循环伏安曲线形状受掺杂阴离子的影响,其电容量与掺杂阴离子的种类及形态有关,阴离子的种类对电极电位和紫外-可见光谱无影响。 相似文献
9.
Narcís Homs Jordi Llorca Montserrat Riera Jordi Jolis Jos-Luis G. Fierro Joaquim Sales Pilar Ramírez de la Piscina 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):251-259
Silica-supported trimetallic catalysts containing Pt, Sn and a group 13 metal (PtSnM, M=Ga, In, Tl) were prepared by consecutive impregnation steps from cis-[PtCl2(PPh3)2] and chloride precursors. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffraction (ED) and energy dispersive X-ray analysis (EDX) showed large platelet-like particles of PtSn1−xMx phases. PtSnGa catalyst with a Pt/(Sn+Ga) molar ratio of 1.72 showed a bimodal particle distribution and a Pt phase was identified. Differences in surface structures were also revealed by the performance of catalysts in the dehydrogenation of n-hexane. For PtSnIn and PtSnTl (Pt/(Sn+M) molar ratio of about 1) the dehydrogenation was favoured. In contrast, PtSnGa catalyst yielded hydrogenolysis products. Photoelectron spectra showed the Pt 4f7/2 level at a binding energy of 70.0–71.8 eV in all cases. Moreover, the FT-IR spectra of chemisorbed CO on the PtSnGa showed a slight shift in the ν(CO) toward higher values with respect to the monometallic catalyst, pointing to an electronic effect in accordance with photoelectron spectroscopy. 相似文献
10.
Shuang-Shuang Yang Ming-Jiang Xie Yu Shen Yong-Zheng Wang Xue-Feng Guo Bin Shen 《中国化学快报》2016,27(4):507-510
Chemical doping of nickel hydroxide with other cations(e.g. Al~(3+)) is an efficient way to enhance its electrochemical capacitive performances. Herein, a simple cation–anion(Ni~(2+)and AlO_2) double hydrolysis method was developed toward the synthesis of nickel–aluminum(Ni–Al) composite hydroxides. The obtained composite hydroxides possesses a porous structure, large surface area(121 m~2/g) and homogeneous element distribution. The electrochemical test shows that the obtained composite hydroxides exhibits a superior supercapacitive performances(specific capacitance of 1670F/g and rate capability of 87% from 0.5 A/g to 20 A/g) to doping-free nickel hydroxide(specific capacitance of 1227 F/g and rate capability of 47% from 0.5 A/g to 20 A/g). Moreover, the galvanostatic charge/discharge test displays that after 2000 cycles at large current density of 10 A/g, the composite hydroxides achieves a high capacitance retention of 98%, indicative of an excellent electrochemical cycleability. 相似文献