排序方式: 共有29条查询结果,搜索用时 31 毫秒
21.
22.
K. Lemański A. G?gor M. Kurnatowska R. P?zik P.J. Dereń 《Journal of solid state chemistry》2011,184(10):2713-2718
In this work, we present for the first time the spectroscopic properties of perovskite nanocrystals CaTiO3: Nd3+, measured at room and liquid nitrogen temperature. Samples were prepared by the sol–gel method and annealed at 700 and 1000 °C. The concentration of Nd3+ ranged from 0.5% to 5%. Average nanocrystallite size primarily depends on the annealed temperature and is about 25 and 50 nm for 700 and 1000 °C, respectively. The absorption, emission and excitation spectra (monitored at 1078 nm) as well as the decay time profile of the emission from the 4F3/2 energy level of Nd3+ are obtained. The increasing amount of Nd3+ ions decreases the lifetime of the 4F3/2 level and that changes from 146 μs for 0.5% to 50 μs for 5% of Nd3+ concentration. The strongest emission was observed at two regions: 1050–1120 nm and 865–930 nm and was assigned to the 4F3/2→4I11/2 and 4F3/2→4I9/2 transitions, respectively. The spectroscopic quality parameter of neodymium in the CaTiO3 lattice has been calculated from the emission spectra. The influence of luminescent properties depending on the annealing temperature and concentration of neodymium ions is discussed. 相似文献
23.
Mixed‐Halide CH3NH3PbI3−xXx (X=Cl,Br, I) Perovskites: Vapor‐Assisted Solution Deposition and Application as Solar Cell Absorbers 下载免费PDF全文
Rahime Sedighi Dr. Fariba Tajabadi Saeed Shahbazi Somayeh Gholipour Dr. Nima Taghavinia 《Chemphyschem》2016,17(15):2382-2388
There have been recent reports on the formation of single‐halide perovskites, CH3NH3PbX3 (X=Cl, Br, I), by means of vapor‐assisted solution processing. Herein, the successful formation of mixed‐halide perovskites (CH3NH3PbI3?xXx) by means of a vapor‐assisted solution method at ambient atmosphere is reported. The perovskite films are synthesized by exposing PbI2 film to CH3NH3X (X=I, Br, or Cl) vapor. The prepared perovskite films have uniform surfaces with good coverage, as confirmed by SEM images. The inclusion of chlorine and bromine into the structure leads to a lower temperature and shorter reaction time for optimum perovskite film formation. In the case of CH3NH3PbI3?xClx, the optimum reaction temperature is reduced to 100 °C, and the resulting phases are CH3NH3PbI3 (with trace Cl) and CH3NH3PbCl3 with a ratio of about 2:1. In the case of CH3NH3PbI3?xBrx, single‐phase CH3NH3PbI2Br is formed in a considerably shorter reaction time than that of CH3NH3PbI3. The mesostructured perovskite solar cells based on CH3NH3PbI3 films show the best optimal power conversion efficiency of 13.5 %, whereas for CH3NH3PbI3?xClx and CH3NH3PbI3?xBrx the best recorded efficiencies are 11.6 and 10.5 %, respectively. 相似文献
24.
The first total synthesis of a thioglycoside analogue of KRN7000, a potential immunostimulant, is described. Two key intermediates are alpha-galactosyl thiol 4 and phytosphingosine derivative 5, which were both prepared from D-galactose. 相似文献
25.
T. Aitasalo P. Dere J. Hls H. Jungner M. Lastusaari J. Niittykoski W. Str
k 《Radiation measurements》2004,38(4-6):515-518
The calcium aluminates doped with the Eu2+ and Nd3+ ions, CaAl2O4:Eu2+,Nd3+, are a novel and efficient persistent luminescence (i.e. afterglow) material. The Nd3+ ions were found to enhance the persistent luminescence. Some other R3+ co-dopants had similar or opposite, though weaker, effect. The Sm3+ (and Yb3+) ions suppressed almost completely the persistent luminescence and thermoluminescence of the Eu2+ ion. From the UV-excited luminescence and persistent luminescence spectra it was found that the Eu2+ ion acts as a luminescent centre with luminescence at the blue (λmax=440 nm) region. The Sm3+ ion was reduced to the divalent state. The thermoluminescence glow curves of the CaAl2O4:Eu2+,Sm3+ material showed that the high-temperature glow peaks, i.e. deep traps, were suppressed almost completely. The Nd:YAG laser-excited high-resolution photoluminescence of the Sm2+ ion confirmed that the Eu2+ ion occupies only one Ca2+ site. Only weak perturbations were observed in the Sm2+ site due to the changes in the environment of the Sm2+ site. 相似文献
26.
We have combined different rare earth ions (Er3+, Nd3+ and Yb3+) in two dimensional ferroelectric patterns to obtain periodical fluorescent arrays. High refractive-index Er3+ doped CaTiO3 nanocrystals have been embedded into Nd3+ or Yb3+ doped LiNbO3 substrates pre-patterned with a two dimensional arrays of micro-voids. The process of incorporation and consolidation of the optically active nanoparticles into the alternate domain structures leads to luminescent ring-shaped arrangements with innovative geometries and to a micrometer spatial control of the trivalent rare earth ion emitters. Multicolor emission systems and the possibility of chromatic switching at the micrometer scale among the different compounds forming the two dimensional structure is demonstrated. 相似文献
27.
Acid-base catalyzed glycosyl donor and then glycosyl acceptor activation with phenylboron difluoride or diphenylboron fluoride permits hydrogen bond mediated intramolecular S(N)2-type glycosidation in generally high anomeric selectivity. 相似文献
28.
The acid-catalyzed reaction of 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-glucopyranose (7) as glycosyl donor with bis-trimethylsilyl sulfide as acceptor affords the α-thiol. Hence, this sterically hindered S-nucleophile as acceptor should provide with O-glycosyl trichloroacetimidates as glycosyl donors that have nonparticipating groups at C-2, glycosylthiols with the thiol group in axial position. This was confirmed for various donors (4, 16-19) with the exception of the corresponding mannosyl donor (20). However, powerful participating groups at C-2 of the donor (23-28) governed the anomeric selectivity. 相似文献
29.
Treatment of 1,6-anhydrosugars with commercially available bis(trimethylsilyl) sulfide in the presence of trimethylsilyl triflate led to the formation of α-glycosyl thiols. All the reactions were highly stereoselective and afforded the α-glycosyl thiols in good to excellent yields. By this procedure, a variety of 1,6-anhydrosugars, differing in their sugar units, glycosidic linkages, and protecting group pattern, were converted smoothly into the corresponding α-glycosyl thiols, which could be of great utility in thioglycoside chemistry. It is noteworthy that 1,6-anhydrosugars carrying the 2-O-acyl group and 1,6-anhydrosugar-containing oligosaccharides could also be ring-opened stereospecifically under the same conditions to give rise to the corresponding 1-thiosugars in high yields. Thus, a very concise and efficient access to α-glycosyl thiols of great value was established. 相似文献