Synthesis, Characterization, and Luminescence Properties of Eu3+ 3-Phenyl-4- (4-toluoyl)-5-isoxazolonate Based Organic-Inorganic Hybrids

Abstract

Organic-inorganic hybrids incorporating Eu(TPI)3·3H2O or Eu(TPI)3·2TOPO [where TPI and TOPO stand for 3-phenyl-4-(4-toluoyl)-5-isoxazolone and tri-n-octylphosphane oxide, respectively] were synthesized either by acetic acid solvolysis or a conventional hydrolysis sol-gel route. The host framework of these materials, named as di-ureasil, consists of a siliceous skeleton grafted, through urea cross-linkages, to both ends of poly(ethylene oxide) chains. The resulting Eu3+-based di-ureasils were characterized by X-ray diffraction and Fourier transform mid-IR, 29Si and 13C NMR, and photoluminescence spectroscopy. The room-temperature photoluminescence (PL) spectra of the Eu3+-based di-ureasils display the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the ground multiplet (7F0–4). Enhanced 5D0 quantum efficiency (η = 13 % vs. 32 %) and a longer lifetime (τ = 0.30 vs. 0.42 ms) was noticed for the hybrid incorporating the Eu(TPI)3·3H2O complex, compared with the undoped complex. The enhancement is explained by the coordination ability of the organic counter part of the host structure, which is strong enough to displace the water molecules of the Eu(TPI)3·3H2O complex from the Eu3+ neighborhood in the hybrids. On the other hand, a decrease in the 5D0 quantum efficiency (η = 76 % vs. 61 %) and lifetime (τ = 0.98 vs. 0.75 ms) was noticed for the hybrid incorporating the Eu(TPI)3·2TOPO complex, relative to the undoped complex, probably because of an increase in the nonradiative transition probability.