Christian Lurin

Energy transfer in a Nd3+-Yb3+ borate glass

Abstract The glasses investigated in the present study had the composition 15Li2O-10BaO-(5-x-y)La2O3-xNd2O3-yYb2O3-3Al2O3-67B2O3 (0 ⩽ x ⩽ 5; 0 ⩽ y ⩽ 5). In singly Nd3+ doped glasses, a slight site-to-site dependence of radiative decay rates has been observed using FLN spectroscopy. Nonexponential decays of neodymium emission were analyzed in terms of microparameters characterizing the probabilities of emission quenching by cross relaxation and of energy migration. In singly Yb3+ doped glasses, the 2F 5 2 → 2F 7 2 emission decay is always exponential. Energy migration over Yb3+ ions arises for y = 1.5 and an ultrafast migration is observed for y #62; 2. In Nd3+-Yb3+ co-doped glasses the Nd3+ → Yb3+ energy transfer probability is quite high. However, a Yb3+ → Nd3+ back transfer exists for low Yb3+ concentrations.

Sol-gel-derived optical pH sensors

The sol-gel process has been successfully used for preparing amorphous and transparent oxide materials doped with organic molecules. This paper reports on the possibility of using sol-gel materials as host matrices for organic dyes in order to perform optical pH sensors. Different materials have been investigated so as to study the influence of some characteristics (porosity, hydrophilicity, hydrophobicity...) on the dye optical behavior. Results will be presented for microporous silica and heteropolysiloxanes which are organic/inorganic composites materials obtained from ormosil precursors known to provide versatile systems. Preliminary experiments have been carried out with sol-gel thin films doped with fluorescein as pH indicator and coated onto flat glass substrates. Dynamic range and response time curves are reported for the different sensors. Problems of signal losses (leachability, dye degradation...), sensor lifetime and dye stability within the different matrices are also discussed.

Interaction Between Host Matrices and Fluorescent Species Trapped in Metal Alkoxides Derived Gels

The sol-gel method has been identified as a very promising direction to prepare host matrices for trapping photoactive species. A wide variety of such activator are sensitive to environmental parameters and have been used both for sot-gel processing investigation and photoactive materials preparation. Depending on the organic or inorganic nature of the fluorescence probe, different fluorescence effects have to be expected in metal oxide matrix derived from a sol-gel process. Special attention has been given to the interaction between three fluorescent species (Eu3+ , Nd3+, pyrene) and three inorganic matrices (silica, titania, zirconia). Fluorescence phenomena have been investigated related to the nature of the probe and its incorporation mode into the host matrix.

Investigation of spatial distribution of neodymium in phosphate glasses by Raman and kinetic luminescence spectroscopy

Abstract Glasses with compositions close to LiLa1−xNdxP4O12 are made up of a network similar to those of the crystallized phosphates LaP3O9, LiLaP4O12 and LaP5O14. The self-concentration quenching of the neodymium emission varies largely with small composition variations and depends on the minimum Nd-Nd distance distribution.

Sol-gel derived β-BBO thin film

(beta) -BaB2O4((beta) -BBO) is known as one of the best inorganic nonlinear crystals. It is now widely used for frequency doubling, frequency mixing in the UV range and optical parametric oscillation in the UV and near infrared regions. To put this material into thin film form would make it very attractive for integrated optical devices. Vacuum deposition techniques are not suitable for the fabrication of borates thin films due to the difficult evaporation or sputtering of oxides based on light elements. The low processing temperature of the sol-gel method allows the formation of stoichiometric and expected oxygen coordination of BaB2O4 in liquid phase. (beta) -BBO thin films has been successfully prepared by the sol-gel method through hydrolysis of barium and boron alkoxides. The accomplishment of hydrolysis is found to be essential for the removal of residual organic at high temperatures. The choice of precursors, hydrolysis ratio, and thermal treatments have critical influences on the formation, the morphology and the nucleation of (beta) -BBO phase of the film. The undesirable interaction between the film and the substrate limits the formation of (beta) -BBO polycrystalline film to only a few selected substrates.

Comparative Study of the Sol-Gel and Metallo-Organic Decomposition (MOD) Processes for the Preparation of Inorganic Materials

Sol-Gel processing and Metallo-Organic Decomposition are contrasted from the thermodynamics and chemical reactivity points of view. Differences and similarities on precursor requirements, processing characteristics, processing intermediates, and product formation pathways are outlined. Some specific examples are presented and their reaction thermodynamics are compared. Some conclusions regarding thermo-dynamic versus kinetic control are drawn from these examples.