Damien Boyer

Synthesis dependent luminescence efficiency in Eu3+ doped polycrystalline YBO3

The influence of the synthesis method on the luminescence efficiency of the orthoborate YBO 3 :Eu 3+ was studied by comparing the optical performances of samples prepared by three routes: solid state reaction (SR), wet process (WP) and sol-gel processing (SG). On the basis of X-ray powder diffraction, SEM micrographs and photoluminescence measurements, SG appears to be the most efficient method to prepare high quality compounds for practical applications. Such a conclusion is reinforced by the existence of an important gain in the luminescence efficiency using this procedure.

Sol–gel waveguide thin film of YBO3: preparation and characterization

Abstract Pure and Eu 3+ ions doped YBO 3 waveguide thin films were dip-coated for the first time through sol–gel route. The quality of the film depends significantly on the dip-coating conditions, especially on environment humidity. We succeeded to prepare crack free thick films with 16 layers and thickness of about 850 nm. It is found that the coating process obeys a two-step kinetics. The films were characterized by different methods, such as m-line spectroscopy, X-ray diffraction, electron microscopy and waveguide fluorescence spectroscopy (WFS). When the annealing temperature is lower than 600°C the film is amorphous and has good waveguide performance. The attenuation of the propagation we have reached is about 0.5 dB/cm. The film starts to crystallize at 700°C. The waveguide performance of the film decreases dramatically with the annealing temperature above 700°C. The result of WFS also indicates that this new kind of thin film is a good host material for active dopants. Our preliminary results show that the new thin film is of great potential for future application in optoelectronics.

Orthoborates processed by soft routes: correlation luminescence structure

Abstract YBO 3 and H–Ln BO 3 (Ln=La, Nd, Sm, and Eu) orthoborates have been prepared by an original sol–gel mineral process. This synthesis method over solid state reaction offers the possibility of obtaining high quality materials at low temperatures, without parasitic phases. Luminescent europium ions have been used as structural probes to investigate these orthoborate phases. Due to the purities of the different powders the symmetries of the europium ion in the different matrices have been determined unambiguously and a comparison between the luminescence results and the structural descriptions given in the literature has been realized.

Local structure of LuBO3 prepared via sol–gel process and its transformation with temperature: 11B-NMR and L-edge XAS studies

Abstract The present work deals with the temperature effect on the stability range of LuBO 3 prepared by sol–gel synthesis. Structural modifications from vaterite to calcite form versus the thermal treatments have been measured by X-ray diffraction and infrared spectroscopy. Several samples derived from the xerogel annealed at 400, 800 and 1200 °C were studied by 11 B solid state NMR and at the lutetium L I –L III edges by X-ray absorption spectroscopy to determine the local atomic arrangement around the rare earth and the boron ions. The predominance of BO 4 groups and the eightfold coordination of lutetium atoms in the LuBO 3 xerogel in samples treated up to 800 °C indicate an evolution of the xerogel to vaterite form after thermal treatment instead of the expected calcite form as established for samples prepared by solid state reaction.

Spectral properties of LuBO3 powders and thin films processed by the sol-gel technique

Abstract Powders and thin films of LuBO3:Eu3+ have been prepared using an original synthesis route, the sol–gel (SG) technique. The derived compounds have been structurally and morphologically characterized confirming the good quality of the synthesized materials obtained by such a process. Both modifications of the structure, from amorphous to the vaterite form for the films and from the vaterite to the calcite for the powders, with the thermal processing have been controlled by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spectral repartition of the laser-induced luminescence of Eu3+ in each form correlates well with the structural descriptions.

Synthesis and characterization of sol–gel derived Y3BO6:Eu3+ powders and films

Abstract Ultra fine powders and thin films of Eu3+ doped Y3BO6 phosphor were synthesized for the first time by the sol–gel method using metal alkoxides as precursors. The formation process and structure of the phosphor powders were investigated by means of infrared, X-ray diffraction (XRD) and scanning electron microscopy. We have also succeeded in preparing crack-free films. From m-lines spectroscopy, XRD and transmission electron microscopy studies, it has been shown that these coatings are uniform and defect-free. Low temperature luminescence spectra recorded from europium doped samples indicate clearly that europium ions occupy at least six different crystallographic sites in the Y3BO6 structure.

Eu-Doped BaTiO3 Powder and Film from Sol-Gel Process with Polyvinylpyrrolidone Additive

Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders revealed spherical and rod shape morphology. The optical quality of films showed a predominant band at 615 nm under 250 nm excitation. A preliminary luminescent test provided the properties of the Eu3+ doped BaTiO3.

Optical properties upon vacuum ultraviolet excitation of sol-gel based Y3Al5O12:Tb3+, Ce3+ powders

Optical properties in the vacuum ultraviolet (VUV) region of cerium and terbium activated Y3Al5O12 powders obtained by the sol-gel process were investigated at room and low temperatures. Both Tb3+ and Ce3+ doped samples exhibited a broad absorption band within the conventional Xe-Ne plasma emission range (140–190 nm). Optimal doping rates have been determined for both rare-earth ions. Emission spectra from cerium doped samples were recorded at 8.2 K and uncovered the splitting of the ground state of Ce3+ ions. Decay times of Ce3+ fluorescence can be fitted by double exponential curves, which can be ascribed to a retrapping phenomenon. Eventually, optical characteristics of codoped Y3Al5O12:(Tb,Ce) and Y3Al5O12:(Tb,Gd) were studied.

V.U.V absorption coefficient measurements of borate matrices

Abstract We present results obtained by direct absorption coefficient measurement on YBO3 thin films in the wavelength range from 120 to 240 nm. Indirect determination of the absorption coefficient by treatment of the low-loss part of electron energy loss spectra has also been investigated. The YBO3 films (few tenths of nanometers) were layered by the Sol-Gel technique on a MgF2 substrate. The results of both experiments are compared. The absorption coefficient of YBO3 is found to be 6.3×105 cm−1 at 147 nm. We show that electron energy loss spectroscopy (EELS) results may be reliable in the low energy range, between 5 and 10 eV.

Modifications induced by acetylacetone in properties of sol–gel derived Y3Al5O12 : Tb3+ – I: structural and morphological organizations

Acetylacetone has been used as a chemical modifier for the synthesis of undoped and Tb(3+)-doped Y(3)Al(5)O(12) powders. A systematic investigation concerning its influence on the structural and morphological properties of amorphous and crystallized samples has been carried out. These properties have been comparatively studied by means of X-ray diffraction, infrared spectroscopy, SEM, XAS and SAXS. (27)Al NMR and EPR experiments have been performed to complete the study. The combined results have evidenced that acetylacetone promotes organic groups departure during calcination, entailing a better structural organization at lower temperatures compared with unmodified powders. Structuration has been proven to occur at short-scale range until a 600 degrees C heating treatment before being extended by coalescence at higher temperatures. Finally, the presence of acac ligands on the alkoxides leads to a monomer-cluster aggregation process, and thus to a more open network.