resumo
This work discusses quantitative aspects of energy transfer occurring in sol-gel derived organic-inorganic di-ureasil hybrids incorporating either [Eu(btfa)3(4,4 '-bpy)(EtOH)] (btfa = benzoyltrifluoroacetonate, 4,4 '-bpy = 4,4 '-bipyridine) or Eu(CF3SO3)(3). Host-to-Eu3+ energy transfer occurs either via ligand singlet and triplet (T) excited states or directly from the hybrid emitting centers through the dipole-dipole, dipole-2(lambda) pole (lambda = 2, 4, and 6) and exchange mechanisms. This latter process is dominant for all discussed energy transfer pathways. The ligand-to-Eu3+ energy transfer rate is typically 1 order of magnitude larger than the value estimated for direct hybrid-to-Eu3+ transfer (3.75 x 10(10) and 3.26 x 10(9) s(-1), respectively, to the D-5(1) level). The most efficient luminescence channel is (S-0)(Hybrid) -> (T)(Hybrid) -> (T)(Ligand) -> (D-5(1), D-5(0)) -> F-7(0-6). The predicted emission quantum yield of the di-ureasil incorporating [Eu(btfa)(3)(4,4 '-bpy)(EtOH)] is in excellent agreement with the corresponding experimental value (53 and 50 +/- 5%, respectively), pointing out that the optimization of the ground state geometry by the Sparkle/AM1 model can, under certain conditions, be implemented in Eu3+-based organic-inorganic hybrids. For di-ureasils incorporating Eu(CF3SO3)(3), the energy transfer rates could not be quantitatively predicted because of the higher computational effort necessary for calculating the singlet and triplet excited states in complex structures, such as these di-ureasils. Instead, the classic Forster and Dexter approaches were applied. Although less efficient, as compared with the di-ureasil incorporating [Eu(btfa)(3)(4,4 '-bpy)(EtOH)], the hybrid-to-Eu3+ energy transfer is also dominated by the exchange (Dexter) interaction.
palavras-chave
BETA-DIKETONATE COMPLEX; FUNCTIONALIZED ORGANIC/INORGANIC HYBRIDS; FULL-COLOR PHOSPHORS; COORDINATION-COMPOUNDS; THEORETICAL APPROACH; LUMINESCENCE PROPERTIES; DIFFERENTIAL-OVERLAP; INTERMEDIATE NEGLECT; LANTHANIDE COMPLEXES; MODIFIED SILICATES
categoria
Chemistry; Science & Technology - Other Topics; Materials Science
autores
Lima, PP; Nobre, SS; Freire, RO; Junior, SA; Ferreira, RAS; Pischel, U; Malta, OL; Carlos, LD