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51.
S. Surendra Babu C.K. Jayasankar W. Sievers G. Wortmann 《Journal of luminescence》2007,126(1):109-120
Phosphate (P2O5+K2O+BaO+Al2O3+Eu2O3) and fluorophosphate (P2O5+K2O+BaO+BaF2+Al2O3+Eu2O3) glasses with different Eu3+ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the 5D0 emitting level of Eu3+ ions in these glasses. The relative luminescence intensity ratio of 5D0→7F2→5D0→7F1 transitions has been evaluated to estimate the local site symmetry around the Eu3+ ions. The emission spectra of these glasses show a complete removal of degeneracy for the 5D0→7F1 and 5D0→7F2 transitions. Second and fourth rank crystal-field (CF) parameters have been calculated together with the CF strength parameter by assuming the C2v symmetry for the Eu3+ ions in both the phosphate and fluorophosphate glasses. Judd-Ofelt parameters have been evaluated from the luminescence intensity ratios of 5D0→7FJ (J=2, 4 and 6) to 5D0→7F1 transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the 5D0→7FJ transitions. Decay curves of the 5D0 level of Eu3+ ions in these two Eu3+:glass systems have been measured by monitoring the 5D0→7F2 transition (611 nm) at room temperature. The experimental lifetime of the 5D0 level in the title glasses is found to be higher than Eu3+-doped niobium phosphate glasses. The analysis indicates that the lifetime of the 5D0 level is found to be less sensitive to the Eu3+ ion concentration and addition of BaF2 has no significant effect on the optical properties of Eu3+-doped phosphate glasses. 相似文献
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G. Wortmann 《Hyperfine Interactions》1986,27(1-4):263-277
A review is given about the current activities in the field of the “synthetic metals”. This nomenclature is used for materials which consist basically of non-metallic components, but reach metallic conductivities by doping or intercalation reactions with additional components acting as donors or acceptors. Typical examples are conducting polymers like doped polyacetylene or graphite intercalation compounds. The contributions of Mössbauer studies in understanding the electronic, magnetic, and structural properties of such systems are outlined. Comparison with other spectroscopic methods is given in selected cases. 相似文献
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C.K. Jayasankar K. Upendra Kumar V. Venkatramu P. Babu Th. Tröster W. Sievers G. Wortmann 《Journal of luminescence》2008,128(5-6):718-720
Emission spectra and decay properties of the 4G5/2 level of Sm3+ ions in TeO2+K2O+Nb2O5 glass have been measured as a function of pressure upto 14.6 GPa at room temperature. A progressive red shift in the barycentres of 4G5/2→6HJ (J=9/2, 7/2 and 5/2) emission bands and increase in splitting of these bands have been observed with increasing pressure. The luminescence decay profile of the 4G5/2 level at ambient condition shows a nearly single exponential nature and with increase in pressure it becomes gradually non-exponential associated with a decrease in lifetime. The non-exponential decay curves are well-fitted to the Inokuti–Hirayama model for S=6, indicating that the interaction for cross-relaxation energy transfer between Sm3+ ions is of dipole–dipole type. The results obtained after release of pressure reveal that there is a small hysteresis. 相似文献
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Arno Müller 《Fresenius' Journal of Analytical Chemistry》1933,95(4-6):166-167
Ohne Zusammenfassung 相似文献
59.
Dimtra Domvoglou Franz Wortmann Jim Taylor Roger Ibbett 《Cellulose (London, England)》2010,17(4):757-770
A combination of techniques have been used to characterise lyocell regenerated cellulose fibre subjected to low-moisture thermal-catalytic reactions with zinc chloride Lewis acid. Application from non-swelling ethanol reduces catalyst accessibility, but at high temperatures migration takes place through the internal fibre morphology. The extent of chain scission is reduced at lower temperatures, leading to a higher leveling-off degree of polymerisation (LODP). In contrast, application of zinc chloride from water results in a lower LODP, due to the more even distribution of catalyst. The weights of extractable polymer material increase according to two separate rate constants, following established semicrystalline models. A higher Arrhenius activation energy for chain scission is seen for zinc chloride application from ethanol, which may be due to the physical mobilisation of the cellulose polymer at high temperature, associated with a cellulose Tg. This may also aid recrystallisation. Cellulose dehydration endotherms and pyrolysis exotherms are shifted to lower temperature for application of zinc chloride from ethanol compared to water, which may be the result of a higher local concentration of catalyst and a faster reaction onset. 相似文献
60.
Striped high-T(c) superconductors such as La(2-y-x)Nd(y)Sr(x)CuO(4) and La(2-x)Ba(x)CuO(4) near x = 1/8 show a fascinating competition between spin and charge order and superconductivity. A theory for these systems therefore has to capture both the spin correlations of an antiferromagnet and the pair correlations of a superconductor. For this purpose we present here an effective Hartree-Fock theory incorporating both electron pairing with finite center-of-mass momentum and antiferromagnetism. We show that this theory reproduces the key experimental features such as the formation of the antiferromagnetic stripe patterns at 7/8 band filling or the quasi-one-dimensional electronic structure observed by photoemission spectroscopy. 相似文献