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排序方式: 共有227条查询结果,搜索用时 906 毫秒
31.
W.Y. Hernández O.H. Laguna M.A. Centeno J.A. Odriozola 《Journal of solid state chemistry》2011,184(11):3014-3020
Ce0.9M0.1O2−δ mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO2 (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F2g Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce4+/Ce3+. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO2, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area. 相似文献
32.
R. N. Bhargava 《Journal of luminescence》1996,70(1-6):85-94
The properties and applications of nanocrystals doped with transition and rare-earth impurities are reviewed. The high efficiency and ultrafast recombination times observed in these doped nanocrystals make these materials very attractive for optoelectronic applications. 相似文献
33.
四磺酸基酞菁氯化铝复合二氧化硅干凝胶的制备及光学性能研究 总被引:2,自引:1,他引:1
采用溶胶凝胶法将不同掺杂浓度的四磺酸基酞菁氯化铝(AlClPcTS)植入二氧化硅凝胶基质,制备了均匀掺杂的复合干凝胶通过对二氧化硅凝胶基质和掺杂AlClPcTS后复合干凝胶孔结构的测定和对复合体系紫外可见吸收光谱的表征,证实了AlClPcTS在基质中的成功掺杂,并发现AlClPcTS同时以单体和二聚体的形式存在于复合体系中,且AlClPcTS二聚体所占比例随着凝胶化过程的进行而增大对不同AlClPcTS掺杂浓度复合干凝胶的光限幅性能进行了测试,并讨论了掺杂浓度对复合体系光限幅性能的影响,证明复合体系的光限幅性能随掺杂浓度的提高而增强. 相似文献
34.
掺杂LiF的ESR谱和ENDOR谱研究 总被引:2,自引:0,他引:2
LiF:Mg,Cu热释光(TL)磷光体在γ辐照后产生F0顺磁中心,其g因子为gxx=2.0030,gyy=2.0450,gzz=2.0251,裂分为Axx=511.04G,Ayy=505.42G,Azz=507.26G。F0中心的浓度随Mg++浓度的增加而下降。磷光体的ENDOR谱显示F0中心附近有铜核存在。照射前和照射后24h测量均未发现Cu++的ESR谱,表明铜是以Cu+形式掺入的,照射并未引起Cu+离子化合价的改变。LiF:Mg,Cu,P在γ辐照前具有轴对称的Cu++离子的ESR谱,辐照后产生了O-空穴中心和PO32-自由基,改变了Cu++的环境,使Cu++的谱发 相似文献
35.
A new approach was developed for quantitative calibration in GD-MS which can afford reliable and metrologically traceable
results for many trace elements and was exemplified for pure copper and pure iron. It can be assumed that the technique can
be further improved and applied to the analysis of other pure metals. Pressed copper and iron powder samples were used to
calibrate the glow discharge mass spectrometry applied to the analysis of pure copper and iron. The new type of glow discharge
mass spectrometer—the Element GD (Thermo Electron Corporation)—was used with a Grimm-type discharge cell for flat samples.
Two series of powder samples were prepared for each of the copper and iron matrixes. The powders were quantitatively doped
with solutions of graduated and defined concentrations of 40 or 20 analytes, respectively. The mass fractions of the analytes
in the dried and homogenized metal powder samples ranged from μg/kg levels up to 10 mg/kg levels. A special technique was
developed to press the samples and to form mechanically stable pellets with low risk of contamination. Ion beam ratios of
analyte ions to matrix ions were used as measurands. The calibration curves were determined and the linear correlation coefficients
were calculated for different intervals of the curves. The linear correlation coefficients are very satisfactory for most
of the calibration curves, which include the higher segments of mass fractions; however, they are less satisfactory for the
lower segments of the calibration curves. Nevertheless, in many cases rather acceptable and rather promising values were achieved
even for these lower segments, representing mass fractions of analytes at ultra-trace level. The comparison of the certified
values of different reference materials with the measured values based on calibrations with the pressed powder samples led
to deviations less than 30% for most of the considered examples.
相似文献
36.
Sushil K. Misra Sergey I. Andronenko Saket Asthana 《Journal of magnetism and magnetic materials》2010,322(19):2902-16348
Four manganite samples of the series, (La1/3Sm2/3)2/3SrxBa0.33−xMnO3, with x=0.0, 0.1, 0.2 and 0.33, were investigated by X-band (∼9.5 GHz) electron paramagnetic resonance (EPR) in the temperature range 4-300 K. The temperature dependences of EPR lines and linewidths of the samples with x=0.0, 0.1 and 0.2, containing Ba2+ ions, exhibit similar behavior, all characterized by the transition temperatures (TC) to ferromagnetic states in the 110-150 K range. However, the sample with x=0.33 (containing no Ba2+ ions) is characterized by a much higher TC=205 K. This is due to significant structural changes effected by the substitution of Ba2+ ions by Sr2+ ions. There is an evidence of exchange narrowing of EPR lines near Tmin, where the linewidth exhibits the minimum. Further, a correlation between the temperature dependence of the EPR linewidth and conductivity is observed in all samples, ascribed to the influence of small-polaron hopping conductivity in the paramagnetic state. The peak-to-peak EPR linewidth was fitted to ΔBpp(T)=ΔBpp,min+A/Texp(−Ea/kBT), with Ea=0.09 eV for x=0.0, 0.1 and 0.2 and Ea=0.25 eV for x=0.33. From the published resistivity data, fitted here to σ(T)∝1/T exp(−Eσ/kBT), the value of Eσ, the activation energy, was found to be Eσ=0.18 eV for samples with x=0.0, 0.1 and 0.2 and Eσ=0.25 eV for the sample with x=0.33. The differences in the values of Ea and Eσ in the samples with x= 0.0, 0.1and 0.2 and x=0.33 has been ascribed to the differences in the flip-flop and spin-hopping rates. The presence of Griffiths phase for the samples with x=0.1 and 0.2 is indicated; it is characterized by coexistence of ferromagnetic nanostructures (ferrons) and paramagnetic phase, attributed to electronic phase separation. 相似文献
37.
采用溶胶凝胶法合成了质子导体BaCe0.7Zr0.1Y0.2O3-δ(BCZY71)纳米粉体,研究了干凝胶到最终钙钛矿结构的转变过程,BCZY71陶瓷块体的电学性能和化学稳定性能。DTA-TG、IR、XRD结果表明经过三个热失重过程可以得到钙钛矿结构的BCZY71样品,1100℃焙烧2h以后可以得到正交相的BCZY71纳米粉末,经过1450℃烧结5h可以得到BCZY71陶瓷块体,BCZY71陶瓷块体的导电行为符合Arrhenius方程,活化能为0.67eV。BCZY71陶瓷块体化学稳定性能显示在100%C02气氛800℃下焙烧2h晶体结构没有发生变化,但是在沸水中煮沸12h以后,大部分钙钛矿结构的BCZY71转变为BaCO3。 相似文献
38.
Justina Jovaišaitė Sven Kirschner Steponas Raišys Gediminas Kreiza Paulius Baronas Saulius Juršėnas Matthias Wagner 《Angewandte Chemie (International ed. in English)》2023,62(4):e202215071
Organic ultralong room temperature phosphorescence (RTP), or organic afterglow, is a unique phenomenon, gaining widespread attention due to its far-reaching application potential and fundamental interest. Here, two laterally expanded 9,10-dimesityl-dihydro-9,10-diboraanthracene (DBA) derivatives are demonstrated as excellent afterglow materials for red and blue-green light emission, which is traced back to persistent thermally activated delayed fluorescence and RTP. The lateral substitution of polycyclic DBA scaffold, together with weak transversal electron-donating mesityl groups, ensures the optimal molecular properties for (reverse) intersystem crossing and long-lived triplet states in a rigid poly(methyl methacrylate) matrix. The achieved afterglow emission quantum yields of up to 3 % and 15 %, afterglow lifetimes up to 0.8 s and 3.2 s and afterglow durations up to 5 s and 25 s (for red and blue-green emitters, respectively) are attributed to the properties of single molecules. 相似文献
39.
A new empirical relation is proposed describing spectral variation of mode-field radius (MFR) as inferred from measurements in the far-field of the fiber. It is shown that using this relation, it is possible to estimate the cut-off wavelength (λc) of the fiber. The proposed technique is successfully tested through measurements made on two standard step index single-mode fibers, as well as on an erbium doped fiber (EDF) having λc falling within its strong absorption band around 980 nm. This empirical formula is more accurate than the widely used Marcuse's formula to describe spectral dependence of MFR determined through measurements made in the fiber's far-field. The proposed technique is especially suited for estimation of λc of doped fibers in which λc falls within an absorption band. 相似文献
40.
钒离子掺杂对TiO2光催化剂薄膜催化活性的影响 总被引:4,自引:0,他引:4
采用溶胶凝胶工艺在普通玻璃表面制备了钒离子非均匀掺杂的TiO2薄膜,运用XRD研究了其光催化复合薄膜的表面特征.以光催化降解甲基橙溶液为模型反应,表征薄膜的光催化活性,结果表明,将钒离子富集在TiO2薄膜内部时,最佳掺杂浓度为1.0%(V/Ti原子百分比),最佳降解表观速率常数为7.44×10-3min-1,约是纯TiO2的2.3倍,有效地提高了TiO2半导体的光催化效率.通过XPS与电化学方法进行分析,说明将钒离子富集在TiO2薄膜内部十分有利于电子-空穴的分离,增强了光生电子与空穴的分离效率. 相似文献