L.D. Carlos

New phosphors based on Eu3+-doped microporous titanosilicates

Abstract Microporous titanosilicate ETS-10 doped with Eu3+ ions is used as a precursor for preparing novel dense materials, analogues of the mineral narsarsukite, which display a high and stable room-temperature luminescence. In the emission spectra of these phosphors a broad band (associated with the network of the titanosilicates) overlaps with the narrow intra- 4 f 6 5 D 0 → 7 F 0–4 lines. The presence of different Eu3+ local site symmetries, tentatively assigned to the C1,2, Cs or C2v point groups, is discussed based on the local field splitting of the 7 F 1,2 energy levels.

Enhanced emission from Eu(III) β-diketone complex combined with ether-type oxygen atoms of di-ureasil organic-inorganic hybrids

Abstract Organic–inorganic hybrids, named di-ureasils and described by polyether-based chains grafted to both ends to a siliceous backbone through urea cross linkages, were used as hosts for incorporation of the well-known coordination complex of trivalent europium (Eu 3+ ) ions described by the formula [Eu(TTA) 3 (H 2 O) 2 ] (where TTA stands for thenoyltrifluoroacetone). By comparing with Eu 3+ -doped di-ureasil without complex form the new materials prepared here enhanced the quantum efficiency for photoemission of Eu 3+ ions. The enhancement can be explained by the coordination ability of the organic counterpart of the host structure which is strong enough to displace water molecules in [Eu(TTA) 3 (H 2 O) 2 ] from the rare earth neighbourhood after the incorporation process. High intensity of Eu 3+ emission was observed with a low non-radiative decay rate under ultraviolet excitation. The quantum efficiency calculated from the decay of 5 D 0 emission was 74%, which in the same range of values previously obtained for the most efficient Eu 3+ coordination compounds reported in literature. Luminescence, X-ray absorption and infrared absorption results considered together leads to a picture where the first coordination shell of Eu 3+ is composed of the 6 oxygen atoms of the 3 β-diketonate ligands and 2 ether-like oxygen atoms of the host.

Magnetic probing of tunable Eu/sup 3+/ local site in organic-inorganic nanohybrids

The magnetic properties of sol-gel derived Eu/sup 3+/-doped organic/inorganic hybrid nanocomposites were studied. These hybrids consist of poly(oxyethylene)-based chains of variable length grafted onto siloxane nanodomains by urea cross-linkages. Results are presented for two chain length series, for which the local environment of Eu/sup 3+/ ions and the urea-urea interactions induce distinct magnetic behaviors. For high Eu/sup 3+/ content strong thermal irreversibility effects are found, due to the presence of Eu/sup 3+/ magnetic interactions in the nanodomains.

Urethane cross-linked poly(oxyethylene)/siliceous nanohybrids doped with Eu3+ ions. Part I: Coordinating ability of the host matrix

Fourier transform mid-IR and Raman spectroscopies were extensively used to examine cation/polymer and cation/cross-link interactions, as well as hydrogen bonding, in Eu 3+ -doped sol-gel derived organic/inorganic materials (monourethanesils). The hybrid framework of these xerogels contains short methyl end capped polyether segments covalently bonded to a siliceous backbone through urethane groups. The cations were incorporated as europium triflate, Eu(CF 3 SO 3 ) 3 . Samples with compositions ∞ > n > 10 (where n indicates the ratio of (OCH 2 CH 2 ) moieties per lanthanide ion) were investigated. The spectral data obtained provided unequivocal evidence that the cations coordinate exclusively to the urethane carbonyl oxygen atoms in compounds with 400 > n ≥ 50. The participation of the ether oxygen atoms of the polymer chains in the Eu 3+ complexation process is initiated at n = 30. The presence of a crystalline phase was detected at n = 10. The variation of the glass transition temperature of the monourethanesils studied with salt concentration is in perfect agreement with these claims. The beginning of the Eu 3+ -polyether interaction is accompanied by a breakdown of the hydrogen bonded aggregates of the matrix, as confirmed by photoluminescence spectroscopy.

Synthesis and Luminescence of Eu3+-Doped Narsarsukite Prepared by the Sol-Gel Process

The sol-gel synthesis and structural characterisation of narsarsukite powders are reported. Samples doped with different Eu3+ amounts (Ti/Eu = 20 and 200), calcined at 800°C, have been characterised by powder XRD, 23Na, 29Si MAS NMR, Raman and luminescence spectroscopies. Eu3+-doped narsarsukite displays a high and stable room-temperature luminescence. The presence in narsarsukite of two different Eu3+ local environments is inferred based both on the distinct 5D0 → 7F0 lines observed and on the local field splitting of the 7F1,2 levels. For low lanthanide contents, the Eu3+ ions are essentially localised in a centrosymmetric environment characterized by a low-energy 5D0 → 7F0 line and a relatively long 5D0 lifetime (3.56–3.96 ms). In contrast, at high lanthanide contents the Eu3+ ions are also present in a second local site with a less covalent first coordination shell. This corresponds to a high-energy 5D0 → 7F0 line and a short 5D0 lifetime (0.84–0.99 ms). Therefore, it is likely that Eu3+ ions substitute for both Ti4+ and Na+, although the former ions are preferentially replaced at low Eu3+ content.

Di-Urethane Cross-linked Poly(oxyethylene)/Siloxane Nanohybrids Doped With Eu(CF 3 SO 3 ) 3

Attractive sol-gel derived di-urethane cross-linked poly(oxyethylene), POE/siloxane hybrids (di-urethanesils) doped with europium triflate, Eu(CF 3 SO 3 ) 3 were examined by Fourier Transform mid-infrared (FT-IR), Raman (FT-Raman) and Photoluminescence spectroscopies with the main goal of elucidating the chemical environment of the cations in these materials. In these hybrids the POE chains contain about 13 oxyethylene repeat units. Samples with compositions ∞ > n ≥ 5 (where n indicates the ratio of (OCH 2 CH 2 ) moieties per Eu 3+ ion) were investigated. The FT-IR and FT-Raman data obtained provided unequivocal evidence that the ether oxygen atoms of the polymer chains start to interact with the Eu 3+ ions at n = 20. The presence of a crystalline POE/Eu(CF 3 SO 3 ) 3 complex was detected at n ≥ 20. Photoluminescence results demonstrated that the doped di-urethanesils studied here are room temperature (RT) efficient full-color emitters. Two distinct cation local sites were unequivocally identified at n = 200 and 20. These Eu 3+ local coordination sites involve the oxygen atoms of the urethane carbonyl groups and weakly coordinated Eu 3+ /CF 3 SO 3 ionic species. For the most concentrated hybrid (n=5) evidences of a third local-environment probably involving the oxygen atoms of the polymer chains was observed.