resumo
Eighteen new Eu3+ complexes and their Gd3+ analogues with 1,3-diketonate as main ligands and N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands were synthesized. The replacement of water molecules by those amides in the Eu3+ complexes increase the intrinsic quantum yields of luminescence, making them comparable or even more efficient than Eu3+ complexes with standard ancillary ligands such as 2,2'-bipyridine. The luminescence spectra of Gd3+ complexes in comparison with the Eu3+ ones show that efficient ligand-tometal intramolecular energy transfer processes take place. In most cases the experimental Judd-Ofelt intensity parameters (Omega(2) and Omega(4)) for the Eu3+ complexes show variations as a function of the temperature (77 and 300K) that overall apparently does not follow clearly any trend. For this reason, geometric variations (on the azimuthal angle phi and ancillary ligands distances) were carried out in the coordination polyhedron for simulating thermally induced structural changes. It has been observed that, in this way, the Omega(2) and Omega(4) can be satisfactorily reproduced by in silica experiments. It was concluded that, at low-temperature, the ancillary ligands become closer to the Eu3+ ion and the angular variations affect more Omega(2) than Omega(4), in agreement to the theoretical calculations. The use of N-(pyridine-2-yl)amides or N-(pyrimidine-2-yl)amides as ancillary ligands in Eu3+ 1,3-diketonates looks to be a good strategy for obtaining highly luminescent complexes.
palavras-chave
TRIPLET-STATE ENERGY; SPECTROSCOPIC PROPERTIES; INTENSITY PARAMETERS; QUANTUM YIELDS; LUMINESCENT PROPERTIES; ELECTRONIC-STRUCTURE; 4F-4F TRANSITIONS; EU(III) COMPLEXES; MIXED COMPLEXES; AB-INITIO
categoria
Optics
autores
Lima, GBV; Bueno, JC; da Silva, AF; Neto, ANC; Moura , RT; Teotonio, EES; Malta, OL; Faustino, WM
nossos autores
Albano Neto Carneiro Neto
Investigador Júnioragradecimentos
The authors thank the following Brazilian agencies for financial support: Conselho Nacional de Desenvolvimento Cientifico e Tecnol.ogico (CNPq), PRONEX-FACEPE-CNPQ, INCT-INEO, and the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES). A.N. C.N. thanks to SusPhotoSolutions -Solucoees Fotovoltaicas Sustent.aveis, CENTRO-01-0145-FEDER-000005.