Energy Transfer Mechanisms in Organic−Inorganic Hybrids Incorporating Europium(III):  A Quantitative Assessment by Light Emission Spectroscopy

Abstract

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(CF 3 SO 3 ) 3 . Host-to-Eu 3+ 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 λ pole (λ ) 2, 4, and 6) and exchange mechanisms. This latter process is dominant for all discussed energy transfer pathways. The ligand-to-Eu 3+ energy transfer rate is typically 1 order of magnitude larger than the value estimated for direct hybrid-to-Eu 3+ transfer (3.75 × 10 10 and 3.26 × 10 9 s -1 , respectively, to the 5 D 1 level). The most efficient luminescence channel is (S 0 ) Hybrid f (T) Hybrid f (T) Ligand f ( 5 D 1 , 5 D 0 ) f 7 F 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 Eu 3+ -based organic-inorganic hybrids. For di-ureasils incorporating Eu(CF 3 SO 3 ) 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 Fo ¨rster 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-Eu 3+ energy transfer is also dominated by the exchange (Dexter) interaction.

EuIII‐Doping of Lamellar Bilayer and Amorphous Mono‐Amide Cross‐Linked Alkyl/Siloxane Hybrids

“…This observation is in good agreement with the existence of hybrid host-to-Eu 3+ energy transfer. [39,40] The energy, fwhm and relative intensity of the intra-4f 6 lines strongly depend on the excitation wavelength, pointing out the presence of distinct Eu 3+ local environments in each hybrid, as discussed in detail below.…”

Lanthanide‐Containing Light‐Emitting Organic–Inorganic Hybrids: A Bet on the Future

“…[182,183] Although the theoretical procedures for using the above equations (reviewed recently by Comby et al [15] and Lima et al [30,179] ) and the corresponding selection rules have been discussed in detail elsewhere, [30,179,182,183] for the sake of simplicity [184] or XRD data.…”

“…The use of Förster and Dexter classic approaches (reviewed recently by Comby et al [15] and Lima et al [179] ) in the investigation of energy transfer processes in organic-inorganic hybrids has been scarcely reported so far. For surfactant-templated mesostructured-silicate thin films containing R6G and Eu 3þ or Tb 3þ complexes, PL and photoexcitation spectra furnish evidence of metal-to-R6G energy transfer.…”

“…[124] For d-U(2000) incorporating Eu(CF 3 SO 3 ) 3 , [179] the following evidences point out that the exchange (Dexter) mechanism accounted for the energy transfer: i) the critical radius calculated according to the Förster model [179] For d-U(600) incorporating [Eu(btfa) 3 (4,4 0 -bpy) (EtOH)], the host-to-ligand and host-to-Eu 3þ energy transfer rates were quantitatively estimated using the data of Table 2, as well as the measured transitions energies, radiative lifetimes, fwhm of the hybrids emitting centers emission, singlet and triplet ligand levels and Eu 3þ intra-4f states, and the average Eu 3þ -ligands and Eu 3þ -hybrids emitting centers distances. [179] Host-to-Eu 3þ energy transfer occurs either via ligand excited states (essentially, the triplet state) or directly from the hybrid emitting centers through the dipole-dipole, dipole-2 l pole, and exchange mechanisms. The host-to-ligand energy transfer is dominated by the exchange mechanism between both diureasil emitting centers and the ligand triplet state, transfer rates between 1.88 and 6.95 Â 10 8 s…”

“…7 F 0-4 intra-4f lines superimposed with the broad band ascribed to the hybrids' emitting centers. [55][56][57][58][59][60][61][62]72,179] The relative intensity of the hybrid-host emitting components also depends on Eu 3þ concentration, so that the higher the Eu 3þ content, the lower relative intensity of the NH/C --O groups and siliceous-related emission, evidencing the presence of energy transfer between the excited states of the hybrid host and the intra-4f 6 levels of Eu 3þ . [58,60,179] The emission also depends on the selected excitation wavelength, [55][56][57][58][59][60][61][62]72,179] displaying the same behavior as that found for the undoped host.…”