Abstract:Este trabalho enfatiza a importância de se distinguir conceitualmente tempos-de-vida na ausência (tempos-de-vida naturais) e na presença de processos de transferência de energia intramolecular em compostos de coordenação com lantanídeos. O foco do artigo trata de compostos de európio trivalente com ligantes mistos, e uma análise de caso é feita sobre resultados apresentados recentemente na literature.This work emphasizes the importance of conceptually distinguishing between lifetimes in the absence (natural li… Show more
“…7. As well demonstrated by Carlos et al, 35 each one of these lifetimes is composed of a sum of reaction rate constants. In principle, both lifetimes can be quenched by the Eu complex in the solid solution.…”
Positronium formation in the bimary molecular solid solutions Tb 1Àx Eu x (dpm) 3 (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the 5 D 4 Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.
“…7. As well demonstrated by Carlos et al, 35 each one of these lifetimes is composed of a sum of reaction rate constants. In principle, both lifetimes can be quenched by the Eu complex in the solid solution.…”
Positronium formation in the bimary molecular solid solutions Tb 1Àx Eu x (dpm) 3 (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the 5 D 4 Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.
“…The density of probability of {L*Tb e + *} formation also depends on the ligand and Eu(III) ion excited state lifetimes. Contrary to what was implicitly stated by Carlos et al, 35 the use of the steady state hypothesis does not lead to a misleading interpretation of the experimentally measured lifetime or of their components, once the steady state hypothesis does not determine these lifetimes, but only an approximated estimation of the ''concentrations'' of the decaying species. In this work, the steady state hypothesis is applied to the formation density probabilities of the different intermediary states of the kinetic mechanism.…”
mentioning
confidence: 66%
“…, nearly the lowest experimental value for the triplet excite state to Eu 3+ ı´on energy transfer rate constant in various Eu(III) b-diketonates, 26,35 and finally k Qlum = k 8Tb + k 9Tb was fixed to its experimental values obtained as shown in Fig. 5.…”
Positronium formation in the bimary molecular solid solutions Tb 1Àx Eu x (dpm) 3 (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the 5 D 4 Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.
“…The two main excitation peaks, 253 (252) nm and 329 (350) nm for Bipy-Dy-TESPIC-MPTMS-SiO 2 ⁄ ZnS and Phen-Dy-TESPIC-MPTMS-SiO 2 ⁄ ZnS can be assigned to the excitation of the p fi p* transition of liangds (Bipy or Phen) and double cross-linking siloxane (TESPIC-MPTMS) derived SiO 2 ⁄ ZnS (Si-O) network. Those f-f transitions within Dy 3+ 4f 9 configuration have also been observed, implying that there exists also an energy transfer from ligand to Dy 3+ in the samples (26). In the emission spectrum, the characteristic transition lines from the lowest excited 4 F 9 ⁄ 2 level of Dy 3+ to 6 H 15 ⁄ 2 (481 nm) and 6 H 13 ⁄ 2 (572 nm) are observed, dominated by the Dy 3+ 4 F 9 ⁄ 2 fi 6 H 13 ⁄ 2 hypersensitive transition (DJ = 2), which are strongly influenced by the outside surroundings and can be served as a very efficient and sensitive structural probe.…”
Section: Resultsmentioning
confidence: 99%
“…The sol‐gel method that is based on hydrolysis/condensation reactions is one kind of mature and economic application technology for preparing inorganic–organic luminescent hybrid materials. This method has unique advantages in synthesizing rare earth organic–inorganic hybrid materials such as low temperature, convenience, versatility and so on (9,10). Meanwhile, by altering the sol‐gel processing conditions, researchers may also control the microstructure, the external shape or the degree of combination between the inorganic and organic phases.…”
Zinc sulfide (ZnS) quantum dot is modified with 3-mercaptopropyltrimethoxysilane (MPTMS) to obtain MPTMS functionalized SiO(2)/ZnS nanocomposite. Novel rare earth/inorganic/organic hybrid materials are prepared by using 3-(triethoxysilyl)-propyl isocyanate (TESPIC) as an organic bridge molecule that can both coordinate to rare earth ions (Eu(3+), Tb(3+), Sm(3+) and Dy(3+)) and form an inorganic Si-O-Si network with SiO(2) ZnS nanocomposite after cohydrolysis and copolycondensation through a sol-gel process. These multicomponent hybrids with double cross-linking siloxane (TESPIC-MPTMS) covalently bonding SiO(2)/ZnS and assistant ligands (Phen = 1,10-phenanthroline, Bipy = 2,2'-bipyridyl) are characterized and especially the photoluminescence properties of them are studied in detail. The luminescent spectra of the hybrids show the dominant excitation of TESPIC-MPTMS-SiO(2)/ZnS unit and the unique emission of rare earth ions, suggesting that TESPIC-MPTMS-SiO(2)/ZnS unit behaves as the main energy donor and effective energy transfer take place between it and rare earth ions. Besides, the luminescent performance of Bipy-RE-TESPIC-MPTM-SiO(2)/ZnS hybrids are superior to that of Phen-RE-TESPIC-MPTMS-SiO(2)/ZnS ones (RE=Eu, Tb, Sm, Dy), which reveals that Bipy or Phen only act as structural ligand within the hybrid systems.
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