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91.
利用高温固相法成功制备了Er~(3+)单掺、Er~(3+)/Yb~(3+)共掺杂Ca_(12)Al_(14)O_(32)F_2上转换发光样品。在980 nm激光激发下,Er~(3+)单掺和Er~(3+)/Yb~(3+)共掺杂样品均呈现出较强的绿光(528,549 nm)和较弱的红光(655 nm)发射,分别归因于Er~(3+)离子的~2H_(11/2),~4S_(3/2)→~4I_(15/2)和~4F_(9/2)→~4I_(15/2)能级跃迁。随着Er离子浓度的增加,单掺杂样品上转换发光强度先增大后减小,最佳掺杂浓度为0.8%。共掺杂Yb~(3+)后,Er~(3+)的发光强度明显增大。还原气氛下合成的样品上转换发光强度增大约两倍,可能和笼中阴离子基团变化有关。发光强度和激发光功率的关系表明所得上转换发射为双光子吸收过程,借助Er~(3+)-Yb~(3+)体系能级结构详细讨论了上转换发射的跃迁机制。 相似文献
92.
《应用有机金属化学》2017,31(4)
Metal–organic framework of NH2‐MIL‐53(Al), with coordinative unsaturated aluminium sites, has been shown to be active in the Groebke–Blackburn–Bienaymé multicomponent coupling reaction based on Ugi‐type amine and aldehyde condensation over isocyanide and then a cyclization process. Interestingly this reaction occurred under solvent‐free conditions with high yield, in which the NH2‐MIL‐53(Al) could be recovered and reused for five reaction cycles, giving a total turnover number of 455. 相似文献
93.
A. J. C. Wilson 《Phase Transitions》2013,86(1-4):125-129
The previous speakers have dealt with tangible physical objects; I am to deal with organizational and symbolic problems. The symbolic problems are of greater scientific importance, but I must begin with those of human organization and in particular with the structure of the International Union of Crystallography (acronym IUCr). 相似文献
94.
Structural and optical properties of 1 at % Al-doped Zn1−xMgxO (x=0–8%) powders prepared by sol–gel method were systematically investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet–visible absorbance measurement, photoluminescence and Raman scattering spectra. All the powders retained the hexagonal wurtzite structure of ZnO. The band gap and near band emission energies determined from absorbance and photoluminescence spectra increased linearly with increasing Mg content, respectively, which implied that the Mg worked effectively on ZnO band gap engineering, irrespective of Al codoping. However, according to the PL and Raman scattering studies, for the sample of x=8%, the Al doping efficiency was decreased by higher Mg codoping. On the other hand, the effect of Mg codoping on photocatalytic degradation of methylene orange was explored experimentally. The substitution of Mg ions at Zn sites shifted the conduction band toward higher energies and then enhanced the photocatalytic activity, while the incorporation of interstitial Mg ions and decreased Al doping efficiency for higher Mg doping sample (x=8%) reduced the photocatalytic activity. 相似文献
95.
《Green Chemistry Letters and Reviews》2013,6(4):335-339
Abstract Hydrotalcite containing magnesium and aluminium (Mg–Al HT) with a molar ratio of Mg(II)/Al(III) = 2.5 has been prepared by a co-precipitation method using the effluent of a Friedel–Crafts acylation reaction. The HT was calcined at 500°C and reconstructed with deionized water. The synthesized HT was characterized by XRD and FT-IR spectroscopy and was successfully used as a catalyst in the Knoevenagel reaction of aldehydes and active methylene compounds. The catalyst was found to be reusable. 相似文献
96.
A simple and convenient method for the aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is achieved via combination of aluminum or ferric nitrates and silica sulfuric acid as environmentally friendly and novel oxidizing media. This oxidation was carried out in dichloromethane under heterogeneous conditions with good to excellent yields. 相似文献
97.
98.
C. Zhu A. Javed P. Li G. Y. Liang P. Xiao 《Surface and interface analysis : SIA》2013,45(11-12):1680-1689
In this study, the initial oxidation behaviour of laser‐treated Al/NiCrAlY bond‐coat is investigated. Two approaches, (i) Al film sputtering on the surface of bond‐coat and (ii) laser treatment, have been taken to enhance the oxidation resistance of NiCrAlY bond‐coat. Experimental results showed that after laser treatment, the Al/NiCrAlY bond‐coat exhibited a columnar dendritic microstructure without cracks and voids. A dense and continuous α‐Al2O3/Cr2O3 multilayer was found to form on the bond‐coat surface. Results on the cyclic oxidation at 1200 °C (for time ≤ 204 h) revealed that the laser‐treated Al/NiCrAlY bond‐coat exhibited better oxidation resistance compared to as‐sprayed NiCrAlY, Al/NiCrAlY and laser‐remelted NiCrAlY bond‐coat. The formation of θ‐Al2O3, NiO, Cr2O3 and NiCr2O4 spinel oxides was observed to be suppressed due to the preformed α‐Al2O3 scale during initial oxidation on the surface of laser pre‐oxidized Al/NiCrAlY bond‐coat. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
99.
FeO/AlO氧载体用于甲烷化学链燃烧:负载量与制备方法的影响 《燃料化学学报》2013,41(11):1384-1392
以不同方法制备了系列Fe2O3/Al2O3氧载体,采用XRD、H2-TPR、CH4-TPR、O2-TPD和BET等分析技术对氧载体进行了表征。研究了不同Fe2O3负载量氧载体的甲烷化学链燃烧性能,考察了不同制备方法对Fe2O3/Al2O3氧载体结构、反应性和产物选择性的影响。结果表明,Fe2O3负载量对氧载体活性及产物中CO2选择性的影响较大,负载量较低时氧载体活性较低且引起甲烷部分氧化产物CO含量增加。制备方法亦对氧载体与甲烷的反应活性有所影响,整体上共沉淀法制备的质量分数60%Fe2O3/Al2O3氧载体具有较高的氧化活性和化学链循环稳定性。其在反应温度850℃、反应时间15 min、30次循环后甲烷转化率及产物中CO2选择性均未见明显降低。 相似文献
100.
采用XRD、N2物理吸附、NH3-TPD以及TEM、IR和NMR手段,系统研究了NaOH碱液后处理对低硅铝比纳米ZSM-5沸石(Si/Al摩尔比为14.5、晶粒度为20~50 nm)孔道和酸度的影响.结果表明,在碱液中,低硅铝比纳米ZSM-5沸石主要发生限域脱硅,而且低硅铝比纳米ZSM-5沸石的碱液脱硅难度大于高硅铝比沸石.但在适当的碱液处理条件下(碱硅比为0.19~0.35,温度为60~80℃,处理时间为2~5 h)可以在其晶体内产生大量介孔,增加比表面积和孔容;同时增加弱酸和中强酸的浓度,并提高L酸比例.L酸的大量增加主要是由于产生了裸露的骨架铝(≡Alδ+),这与文献的观点有所不同. 相似文献