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71.
Fluorescence quantum yields and lifetimes of coumarin dyes are sharply reduced in polar solvents if amine substituent groups are free to rotate. The polar solvent effect is interpreted in terms of relaxation of excited dye from an initial planar conformation to a twisted zwitterionic state. 相似文献
72.
K.L. Holman Q. Huang K. Trzebiatowski E. Morosan R.J. Cava 《Journal of solid state chemistry》2007,180(1):75-83
The double perovskites La2CoVO6, La2CoTiO6, and La2NiVO6, are described. Rietveld fitting of neutron and powder X-ray diffraction data show La2NiVO6 and La2CoVO6 to have a disordered arrangement of B-cations whereas La2CoTiO6 shows ordering of the B-cations (with ∼5% Co/Ti inversion). Curie-Weiss fits to the linear region of the 1/χ plots reveal Weiss temperatures of −107, −34.8, and 16.3 K for La2CoVO6, La2CoTiO6, and La2NiVO6, respectively, and magnetic transitions are observed. La2CoTiO6 prepared by our method differs from material prepared by lower-temperature routes. A simple antiferromagnetic spin model is consistent with the data for La2CoTiO6. These compounds are semiconductors with bandgaps of 0.41 (La2CoVO6), 1.02 (La2CoTiO6) and 0.45 eV (La2NiVO6). 相似文献
73.
Xiaofei Han Run Liu Zhude Xu Weixiang Chen Yifan Zheng 《Electrochemistry communications》2005,7(12):1195-1198
Nanocrystalline cadmium peroxide thin film has been electrodeposited on indium doped tin oxide glass substrate from aqueous solution at room temperature. The grain size of the nanocrystals of the film is estimated from XRD and is about 14 nm. The deposits are decomposed at 228 °C by formation of CdO, releasing plentiful heat at same time. The band-gap of the nanocrystalline CdO film made from decomposition of electrodeposited CdO2 is around 2.4 eV. 相似文献
74.
Berberine chloride (1) upon treatment with NaOAc-Ac2O yields naphthalene derivatives 4 and 5 In like fashion, 8 gives naphthalene 10; isoquinoline methiodide leads to β-naphthyl acetate; and 12 provides 14. The reaction has been extended to the 3-carbonyl pyridinium series where 3-acetylpyridine methiodide and 3-pyridinecarboxaldehyde methiodide furnish lactones 16 and 17, respectively. All these transformations proceed by initial nucleophilic attack of the acetic anhydride anion on the immonium carbon atom. 相似文献
75.
A rapid spectrophotometric method has been developed for the stepwise determination for mercury, cadmium, and zinc in mixtures. Optimal conditions have been established for the extraction efficiency of cadmium and mercury with a chloroform solution of tribenzylamine pre-equilibrated with hydrobromic acid. After addition of dithizone solution to the organic layers the absorbance at 490 nm or 510 nm is measured for mercury or cadmium, respectively. Even when the ratio of mercury, cadmium, and zinc is 10-1 : 1 : 10-5 , the metals can be determined successively. 相似文献
76.
77.
A novel synthesis methodology is reported for the preparation of NiS submicron particles in a green solvent 1-butyl-3methylimidazolium tetrafluoroborate (BMImBF4) ionic liquid (IL), using ultrasonic sonochemical technique. Structural, morphological and optical properties of nickel sulfide powders were obtained by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS). Composition was corroborated by energy dispersive X-ray spectroscopy (EDXS), both in the SEM and in the TEM. Regular shape particles were obtained under high-intensity ultrasonic irradiation for 105 min from the reaction between nickel nitrate and thioacetamide in ethanol/BMImBF4 (80:20), respectively. After vacuum annealing treatment at 180 °C overnight, spherical crystalline NiS particles were observed. The powders showed a band gap of 0.74 eV. 相似文献
78.
Scott Gaynor Dorota Greszta Daniela Mardare Mircea Teodorescu Krzysztof Matyjaszewski 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1561-1578
Various methods which lead to the control of molecular weight and polydispersities, and which allow for the preparation of block copolymers by radical polymerization are discussed. Thermal polymerizationof styrenes in the presence of stable radicals, polymerization of vinyl acetate and methyl methacrylate in the presence of chromium complexed by macrocyclic ligands polymerization of vinyl acetate initiated by organoaluminum compounds complexed by dipyridyl and activated by stable radicals, as well as in the presence of phosphites, are described in detail. 相似文献
79.
Time-resolved magneto photoluminescence in a diluted magnetic semiconductor Cd 0.9 Mn 0.1 Te has been carried out with varying exciton density from 10 14 to 10 19 cm m 3 . The reduction of the Zeeman shift and that of the magnetic polaron energy was found under strong photoexcitation. The spectral feature is interpreted in terms of the heating of the manganese spin subsystem. Polarization dependence of the spin heating is observed for the first time, revealing the contribution of the spin flip between excitons and magnetic ions to the heating process. 相似文献
80.
The nature and relative contributions (RCs) of various radiative recombination processes to the photoluminescence (PL) spectra for bulk nanostructured Pb0.30Cd0.70I2 solid solutions have been established at different temperatures. The analysis indicates that the PL is caused by free, bound and self-trapped excitons as well as by donor-acceptor pairs emission with the participation of shallow and deep acceptor centers. It was shown that X-ray luminescence (XRL) spectra are also determined by these recombination processes. However, their RC and the temperature evolution are considerably different. Besides, XRL spectra contain an intense long-wavelength band associated with the emission of many LO-phonons. It was shown that the deep luminescence surface states, associated with the self-trapped excitons and deep intrinsic defects, mainly determine the intensity of XRL spectra both at 80 K and room temperature. The results obtained open the way to the optimization of the scintillator properties of the investigated materials. 相似文献