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61.
62.
M. Sc. Stephanie Kindt Karina Wicht Prof. Dr. Markus R. Heinrich 《Angewandte Chemie (International ed. in English)》2016,55(30):8744-8747
The radical carbohydroxylation of styrenes with aryldiazonium salts has been achieved under mild thermal conditions. A broad range of aryldiazonium salts was tolerated, and the reaction principle based on a radical–polar crossover mechanism could be extended to carboetherification as well as to a two‐step, metal‐free variant of the Meerwein arylation leading to stilbenes. 相似文献
63.
Efficient and selective removal of 90Sr is an important process for the safe use of nuclear energy. Herein, we investigate and assess the Sr2+ adsorption properties of a metal-organic framework UiO-66-(COOH)2 functionalized by non-bonded carboxylic groups. This MOF is an exciting class of free carboxylic functionalized MOFs that combine chemical stability with gas sorption, dye elimination, and conductivity. Specifically, we show that uniformly distributed carboxyl and water stability make it accessible for loading Sr2+ without structural changes. The FTIR spectroscopy, PXRD analysis, XPS, and SEM-EDS studies show excellent stability as well as the strong affinity between -COOH active site and Sr2+. This strong coordination interaction guarantees a high adsorption capacity of 114 mg g−1 within 5 h (pH 5 and 298 K). Combined kinetic and thermodynamic studies show that the surface complexation is strong chemisorption and cost-effective spontaneous process (ΔG = −5.49 kJ mol−1~−2.16 kJ mol−1). The fact that UiO-66-(COOH)2 not only possesses a high adsorption capacity, but also enables selectivity to Sr2+ in the presence of similar radius ions Na+ and K+, prefigures its great potential for the practical treatment of radioactive Sr2+ in polluted water. 相似文献
64.
Luk Fojt Bohumír Grüner Jan Nekvinda Ece Zeynep Tzn Ludk Havran Miroslav Fojta 《Molecules (Basel, Switzerland)》2022,27(6)
In this study we explore the effect on the electrochemical signals in aqueous buffers of the presence of hydrophilic alkylhydroxy and carboxy groups on the carbon atoms of cobalta bis(dicarbollide) ions. The oxygen-containing exo-skeletal substituents of cobalta bis(dicarbollide) ions belong to the perspective building blocks that are considered for bioconjugation. Carbon substitution provides wider versatility and applicability in terms of the flexibility of possible chemical pathways. However, until recently, the electrochemistry of compounds substituted only on boron atoms could be studied, due to the unavailability of carbon-substituted congeners. In the present study, electrochemistry in aqueous phosphate buffers is considered along with the dependence of electrochemical response on pH and concentration. The compounds used show electrochemical signals around −1.3 and +1.1 V of similar or slightly higher intensities than in the parent cobalta bis(dicarbollide) ion. The signals at positive electrochemical potential correspond to irreversible oxidation of the boron cage (the C2B9 building block) and at negative potential correspond to the reversible redox process of (CoIII/CoII) at the central atom. Although the first signal is typically sharp and its potential can be altered by a number of substituents, the second signal is complex and is composed of three overlapping peaks. This signal shows sigmoidal character at higher concentrations and may be used as a diagnostic tool for aggregation in solution. Surprisingly enough, the observed effects of the site of substitution (boron or carbon) and between individual groups on the electrochemical response were insignificant. Therefore, the substitutions would preserve promising properties of the parent cage for redox labelling, but would not allow for the further tuning of signal position in the electrochemical window. 相似文献
65.
通过Sol-gel(溶胶-凝胶)技术,首次将Al3 离子和K 离子同时引入到掺Er3 硅酸盐玻璃中,并测定了硅基玻璃中Er3 离子的吸收光谱、透射光谱、光致发光光谱(PL谱)、上转换光谱、拉曼光谱及荧光寿命.结果显示:掺入的Al3 离子和K 离子不但分别使Er3 离子的荧光强度增强20倍和70倍,而且使Er3 离子在1 532 nm处的荧光寿命从4.8 ms延长至7.1和11.2 ms,但经过进一步分析可知两者对其的影响机制却完全不同;同时作者发现,在980 nm波长激发下,Er3 离子的上转换荧光应该同时存在两种发光机制:双光子吸收和能量传递上转换. 相似文献
66.
采用水热法合成了不同粒径的NaLa(MoO4)2∶Eu3+微晶.通过调节乙二醇浓度和反应时间,研究了NaLa(MoO4)2∶Eu3+微晶的形貌演变过程,在水热条件下180 ℃反应16 h获得了均一梭子形NaLa(MoO4)2∶Eu3+微晶,其晶粒长度约为2.0 μm.荧光光谱分析表明,Eu3+取代了NaLa(MoO4)2中La3+的格位, Eu3+在613 nm处红光发射(5D0–7F2跃迁)的浓度猝灭机理是电偶极-电四极相互作用,并发生了Eu3+( 5D1 ) + Eu3+(7F0 )→ Eu3+( 5D0 ) + Eu3+(7F3) 交叉弛豫,由此导致浓度猝灭.
关键词:
钼酸盐
水热法
稀土离子
发光 相似文献
67.
Comparative analysis of the luminescent properties of Y3Al5O12:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where YAl antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of YAl antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200-470 nm range related to YAl antisite defects and charged oxygen vacancies (F+ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce3+ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce3+ ions. 相似文献
68.
N.A. Kulagin 《Journal of luminescence》2011,131(3):526-530
Selected data of ab initio simulation of the electronic structure and spectral properties of either cluster with ions of iron, rare earth or actinium group elements have been presented here. Appearance of doped Cr+4 ions in oxides, Cu+2 in HTSC, Nd+2 in solids has been discussed. Analysis of experimental data for plasma created ordered structures of crystallites with size of about 10-9 m on surface of separate oxides are given, too. Change in the spectroscopic properties of clusters and nano-structures on surface of strontium titanate crystals discussed shortly using the X-ray line spectroscopy experimental results. 相似文献
69.
Fluorophosphate glasses of composition, P2O5 + K2O + KF + MO + Al2O3 + xEu2O3 (M = Mg, Sr and Ba; x = 0.01, 0.05, 0.1, 1.0, 2.0, 4.0 and 6.0 mol%) were prepared and characterized their optical properties. Crystal-field (CF) analysis revealed a relatively weak CF strength around Eu3+ ions in the Ba based fluorophosphate glasses. The Judd-Ofelt parameters have been estimated from the oscillator strengths of 7F0 → 5D2, 7F0 → 5D4 and 7F0 → 5L6 absorption transitions of Eu3+ ions and were used to evaluate the radiative properties of the 5D0 → 7FJ (J = 0-4) transitions. Considerable variation has been observed in the relative intensity ratio of 5D0 → 7F2 to 5D0 → 7F1 transitions of Eu3+ ions due to change in the alkaline earth metal ions. The decay of the 5D0 level shows single exponential and less sensitive to Eu3+ ions concentration as well as MgO/SrO/BaO modifiers. 相似文献
70.
Photoluminescence spectra of thenardite Na2SO4 activated with rare-earth ions, Ce, Sm, Tb, Dy and Tm
Five Na2SO4:RE3+ phosphors activated with rare-earth (RE) ions (RE3+=Ce3+, Sm3+, Tb3+, Dy3+ and Tm3+) were synthesized by heating natural thenardite Na2SO4 from Ai-Ding Salt Lake, Xinjiang, China with small amounts of rare-earth fluorides, CeF3, SmF3, TbF3, DyF3 and TmF3, at 920 °C in air. The photoluminescence (PL) and optical excitation spectra of the obtained phosphors were measured at 300 and 10 K. In the PL spectrum of Na2SO4:Ce3+ at 300 K, two overlapping bands with peaks at 335 and 356 nm due to Ce3+ were first observed. Narrow bands observed in PL and excitation spectra of Na2SO4:RE3+ (RE3+=Sm3+, Tb3+, Dy3+ and Tm3+) phosphors were well identified with the electronic transitions within the 4fn (n=5, 8, 9 and 12) configurations of RE3+. The existence of excitation bands with high luminescence efficiency at wavelengths shorter than 230 nm is characteristic of Na2SO4:RE3+ (RE3+=Sm3+, Tb3+, Dy3+ and Tm3+) phosphors. The obtained results suggest that these phosphors are unfavorable as the phosphor for usual fluorescence tubes, i.e., mercury discharge tubes, but may be favorable as the phosphor for UV-LED fluorescent tubes and as cathodoluminescence, X-ray luminescence and thermoluminescence phosphors. 相似文献