Two anionic surfactants, dodecylsulfate (DDS) and dodecylbenzenesulfonate (DBS), were intercalated into layered zinc hydroxide salts (LHS) using the direct alkaline co-precipitation method, and characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) and thermogravimetric analysis/differential thermal analysis (TGA/DTA). Different UV-absorbing organic molecules, like salicylates, cinnamates and benzophenones, were adsolubilized in the LHS interlayer following two different procedures (conventional microwave treatment and microwave with hydrothermal treatment). The adsolubilized products were investigated by PXRD, FTIR, diffuse reflectance UV-Vis (DRUV-Vis) and luminescence spectroscopies before and after exposure to UV radiation. Most of the products showed a good absorption in the UV region, from UVC to UVA, and good stability under UV radiation. The photodegradation tests showed that DDS-intercalated compounds were more stable than those intercalated with DBS. Adsolubilization in LHS can be an interesting alternative to immobilize neutral molecules with UV absorption capability, to prepare materials to be used in sunscreen formulations.

Guias de luz planares foram obtidos a partir de um sol de um novo híbrido Ti4+-acetilacetona (acac)-Ureasil depositado na forma de filmes finos sobre substratos de vidro. A estrutura foi investigada por medidas espectroscópicas (absorção no infravermelho, fotoelétrons de raios-X e espalhamento Raman) e espalhamento de raios-X a baixos ângulos (SAXS). Para a adição do complexo Ti-acac ao ureasil na razão molar Ti:Si de 1:1 interações entre o complexo Ti-acac e grupos siloxanos foram identificadas. Quantidades maiores de Ti4+ (razão molar Ti:Si de 5:1) levam também à formação de nanoagregados ricos em titânio. Os parâmetros ópticos dos guias, como índice de refração, espessura, modos propagados e coeficiente de atenuação foram medidos para 632,8, 543,5 e 1550 nm pela técnica de acoplamento de prisma. O índice de refração pode ser controlado pela quantidade relativa de titânio. Guias de poucos micra de espessura suportam modos de propagação com baixas perdas para todas as composições.

Hybrid planar waveguides were prepared from Ti4+-acetylacetone (acac)-Ureasil sols deposited on glass substrates. Structural features have been investigated by spectroscopic measurements (Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Raman scattering) and Small Angle X-ray Scattering (SAXS). Addition of Ti4+-acac to the ureasil (Ti:Si molar ratio 1:1) leads to the formation of bonds between the Ti complex and the siloxane groups, whereas further addition of Ti4+ (Ti:Si molar ratio 5:1) leads to the additional formation of titanium-rich nanoclusters. The optical parameters of the waveguides such as refractive index, thickness, propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique. The refractive index can be tuned by the Ti4+ relative content. The few microns thick planar waveguides support well confined propagating modes with low attenuation loss for all compositions.

In this article we review some of the basic aspects of rare earth spectroscopy applied to vitreous materials. The characteristics of the intra-atomic free ion and ligand field interactions, as well as the formalisms of the forced electric dipole and dynamic coupling mechanisms of 4f-4f intensities, are outlined. The contribution of the later mechanism to the 4f-4f intensities is critically discussed, a point that has been commonly overlooked in the literature of rare earth doped glasses. The observed correlation between the empirical intensity parameter W2 and the covalence of the ion first coordination shell is discussed accordingly to the theoretical predictions.

Eu3+ luminescence and EXAFS (Extended X-ray Absorption Fine Structure) results are presented for organic-inorganic hybrid gel hosts composed of a siliceous network to which small chains of oxyethylene units are covalently grafted by means of urea bridges. Coordination numbers for Eu3+ ions range from 12.8 to 9.7 with increasing Eu3+ concentration while the Eu3+-first neighbours mean distance is found to be constant at 2.48-2.49 Å in the same concentration range. Emission spectra display a broad band in the green/blue spectral region superposed to narrow lines appearing in the yellow/red region in such a way that for the eyes emission appears white. The broad band is assigned to intrinsic NH groups emission and also to electron-hole recombination in the nanosised siliceous domains. The narrow lines are assigned to intra-4f6, 5D0->7F0-4 Eu3+ transitions and from the energy position of the 7F0-4 levels a mean distance could be calculated for the Eu3+-first neighbours. The calculated results are in good agreement with the experimental ones obtained from EXAFS analysis.