Temperature-driven luminescence switching of europium(III) in a glass dispersed liquid crystal film

Glass dispersed liquid crystal films doped with the tris(beta-diketonato)europium(III) complex [Eu(dbm)(3)(gly)] (Hdbm = dibenzoylmethane, gly = 1,2-dimethoxyethane) were prepared. The liquid crystal host was 4-pentyl-4'-cyanobiphenyl (5CB); a mixed silica-titania glass with a refractive index close to that of 5 CB was chosen as the glass matrix. The photoluminescence intensity was measured as a function of temperature. A strong intensity change was observed at the nematic-to-isotropic transition.status: publishe

Temperature-driven luminescence switching of europium(III) in a glass-dispersed liquid crystal film

Dispersed liquid crystal displays are a more recent type of LCD and involve micrometer-sized droplets of a nematic liquid crystal in a solid, isotropic matrix.1 Polymer dispersed liquid crystals are now well studied. The sol-gel process can be used for preparing films of Glass Dispersed Liquid Crystals (GDLCs).2 The glass films have dispersed liquid-crystalline droplets with a diameter varying between 1 and 180 μm. Here, a simple type of GDLC was used to test the application of lanthanide-doped luminescent GDLC films. The samples were prepared by a sol-gel synthesis starting from tetraethyl orthotitanate, an amine functionalized organoalkoxysilane and water. The incorporation of a liquid crystal (5CB) in the sol-gel film and the solubility a europium(III) β-diketonate complex in this matrix was tested. The variation of the luminescence intensity of a europium(III) complex as a function of the temperature was recorded. The liquid crystal in the nematic phase scatters incident light very strongly. In a GDLC film the droplets containing liquid crystal cause the whole sample to be turbid. UV-light was used to excite the luminescent compound. Due to the large internal scattering of the UV-light in the nematic phase the absorption by the luminescent dopand is enhanced, thus giving the layer a visible red color. When the film is heated above the clearing point, the refractive index of the isotropic liquid becomes similar to the refractive index of the glass. The UV-light passes through the layer with less absorption, and thus less luminescence light is produced. A strong change in the luminescence intensity was observed at the nematic-to-isotropic transition. References (1) Higgins, D.A., Adv. Mater. 2000, 12, 251. (2) Levy, D., Serna, C.J., and Oton, J.M., Mater. lett. 1991, 10, 470.poster presented by Kris Driesenstatus: publishe

Preparation of hydrophylic ionic liquids using a silver-free metathesis reaction

poster presented by Ben Thijsstatus: publishe

A luminescent tris(2-thenoyltrifluoroacetonato) europium(III) complex covalently linked to a 1,10-phenanthroline-functionalised sol-gel glass

Lanthanide doped sol-gel glasses are an attractive type of luminescent material which can be processed at ambient temperatures. However, the solubility of the lanthanide complexes in the sol-gel matrix can be a problem and it is difficult to obtain a uniform distribution of the complexes ( avoidance of cluster formation). These problems can be solved by covalently linking the lanthanide complex to the glass matrix. In this study, a strongly luminescent europium beta-diketonate complex was immobilized on a 1,10-phenanthroline-functionalised silica sol-gel glass. The glass matrix was prepared by first reacting 5-amino-1,10-phenanthroline with 3-(triethoxysilyl) propyl isocyanate. The resulting compound, tetramethoxysilane ( TMOS) and diethoxydimethylsilane ( DEDMS) were hydrolysed and condensed at a neutral pH to a sol-gel glass. A tris(2-thenoyltrifluoroacetonato) europium(III) dihydrate complex was bound to the 1,10-phenanthroline groups on the silica gel and the coordinated water was expelled. High-resolution luminescence spectra were recorded and the radiative lifetimes were measured. It is shown that the spectroscopic behaviour of the luminescent materials is very comparable with that of the pure [Ln(tta)(3)(phen)] complex.status: publishe

A luminescent tris(2-thenoyltrifluoroacetonato)europium(III) complex covalently linked to a 1,10-phenanthroline-functionlised sol-gel glass

oral presentation by Philip Lenaertsstatus: publishe

Judd-Ofelt analysis of lanthanide doped silica-PEG hybrid sol-gels

Lanthanide complexes of 1,10-phenanthroline (phen), 2,2'-bipyridine (bipyridyl, bpy) and dipicolinate (dpa), together with uncomplexed lanthanide ions (Ln = Nd, Sm, Dy, Ho, Er) were doped into silica-polyethylene glycol (SiO2 PEG) inorganic organic hybrid materials. The samples were prepared via a sol-gel process. The intensities of the f-f transitions in the absorption spectrum were analysed by application of the Judd-Ofelt theory. Sets of phenomenological Omega(lambda) intensity parameters have been extracted. The hypersensitive transitions are strongly influenced by the drying time of the sol-gel glass. The PEG molecules compete with the organic ligand for complex formation to the lanthanide ions complex. 1,10-Phenanthroline and bipyridyl complexes are not stable in the presence of PEG, but the dipicolinate complexes are.status: publishe

Influence of heat treatment on the intensities of f-f transitions in lanthanide-doped sol gel glasses

Optical absorption spectra of monolithic silica sol gel glasses incorporating the lanthanide complexes [Ln(bpy)(2)]Cl-3, [Ln(phen)(2)]Cl3 and Ln(NO3)3 (bpy = bipyridyl, 2,2'-bipyridine, phen = 1,10-phenanthroline, Ln = Nd, Sm, Dy, Ho, Er) were recorded. The Judd-Ofelt theory was used to study changes in the coordination sphere before and after water was expelled from the glass matrix by heat treatment. The intensity of the hypersensitive transitions was found to increase significantly, which is reflected by an increase in the Ohm(2) intensity parameter. The non-hypersensitive transitions are influenced by the native sol gel matrix rather then by the type of ligands. The Ohm(4) and Ohm(6) parameters remain more or less constant upon heat treatment. In accordance with theoretical predictions the values of both Omega(4) and Omega(6) of the lighter lanthanides are larger than those of the heavy lanthanides.status: publishe