Jacques Mugnier

Frequency conversion of light by intramolecular energy transfer in bifluorophoric molecules

Abstract A new type of bifluorophoric molecule consisting of two coumarins linked by a short saturated chain is studied. The energy transfer efficiency is close to I and a good photochemical stability is expected. Therefore, this type of compound is well suited for efficient frequency conversion of light and can thus be used in various applications such as scintillators or fluorescent solar concentrators.

Rate of intramolecular electronic energy transfer in coumarin bichromophoric molecules. An investigation by multifrequency phase-modulation fluorometry

Abstract Dynamics of intramolecular electronic energy transfer in bichromophoric molecules, consisting of two coumarins linked by a variable number of methylene groups, is investigated by multifrequency phase-modulation fluorometry. From observation of the acceptor delayed emission, information on the rate of transfer can be obtained.

A New Elaboration Route by Sol-Gel Process for Cerium Doped SrHfO3 Films and Powders

We present for the first time the elaboration via sol gel route of cerium (1 mol%) doped SrHfO3 powders and films. The sol is elaborated using hafnium and strontium ethoxides as precursors and cerium nitrate as dopant. The structure of powders and films are characterized by convergent methods: Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, Raman spectroscopy and optical measurements conducted by the prism coupling method. The powder crystallises from amorphous to pure SrHfO3 orthorhombic perovskite phase after a 800°C heat treatment. Nevertheless HfO2 monoclinic phase coexists with orthorhombic perovskite phase after a 1000°C heat treatment. The film is amorphous for annealing temperatures lower than 700°C and presents good waveguiding performances. The film heat-treated at 700°C exhibits a refractive index of 1.810 ± 0.001 (λ = 543.5 nm) for a thickness around 375 nm. The attenuation coefficient obtained on the 400°C heat-treated film is α = 4.0 ± 0.5 dB/cm (λ = 632.8 nm). The film starts to crystallize at 750°C into the SrHfO3 orthorhombic phase but HfO2 monoclinic phase is also detected after a heat treatment at 1000°C. The potentiality of sol gel Ce3+:SrHfO3 powders and films for scintillation applications are investigated.

High-quality sol-gel thin films: elaboration, studies in waveguiding configuration, and application to sol-gel scintillators

The sol gel process is a rather simple route for the elaboration of pure or doped well known oxides such as TiO2, ZrO2, ... or less usual oxides such as Lu2O3, Gd2O3... in thin film form. A proof of the high optical quality of the layers is their ability to propagate light even if their application is not in the waveguide field. Moreover waveguiding properties of the layers allow their studies in waveguiding configuration. Among these methods, the most attractive for the sol gel films is the very low frequency waveguide Raman which provides the nanocrystals sizes and phases according to the annealing temperatures as illustrated by ZrO2 sol gel layers studies. For such measurements the thin films must be very carefully elaborated as described in this presentation. As example of application, Gd2O3 sol gel scintillating films are presented, when studied in waveguiding configuration and used in transmission configuration. The sol elaboration is described. The thickness and the refractive index of the films are analysed as a function of the annealing treatment. Results of the europium doped gadolinium oxide layer under X rays excitation are presented which underlined the attention paid on all the steps of the elaboration procedure.

Application of multi-wavelength m-lines spectroscopy for optical analysis of sol-gel prepared waveguide thin films

M-lines spectroscopy (MLS) is an accurate, to within 10-3-10-4, nondestructive technique for measuring optogeometric parameters (refractive index and thickness) of thin planar step-index waveguide films. Two exciting polarizations can be used and information about the film anisotropy derived. Usually, MLS uses only one wavelength, which may be disadvantageous in some cases. We have developed an MLS setup that includes a set of lasers emitting in the range of 405 to 1550 nm to conduct multi-wavelength MLS (MWMLS). MWMLS offers an opportunity to obtain more detailed optical information, e.g., index profiles and dispersion curves, especially important for sol-gel prepared waveguide thin films that are relatively porous and whose structure depends on the annealing treatment. The paper presents a detailed description of the MWMLS setup. By using sol-gel prepared waveguide thin films of Y2O3, HfO2:Eu3+, and TiO2, optical measurements are exemplified. Proceeding from the measurements, the advantages and limitations of the method are discussed.

Preparation and characterization of sol-gel-derived YAG optical planar waveguide

YAG optical planar waveguide was elaborated through sol-gel method. Acetate-alkoxide (YAG-I) and 2-alkoxides (YAG-II) methods were used for the sol preparations. The as-deposited layers were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), m-lines, spectroscopy (MLS) Rutherford Backscattering Spectroscopy (RBS) and waveguide Raman spectroscopy (WRS). No intermediate phases were observed for both synthesis routes. In comparison, (YAG-II) layers presented a better adherence than YAG-I to SiO2 substrate, a higher refractive index and allowed to form a pure phase of YAG at lower temperature and short heat duration (900°C for 10min). However, the interdiffusion of Al and Si ions were detected to influence the refractive index improvement by heat treatments. The propagation loss of the fabricated YAG thin films in amorphous phase can be as low as 1.5±0.3 dB/cm.

Influence of annealing temperature on composition and stresses of alumina thin films elaborated by the sol-gel method

Alumina thin films were elaborated by the sol-gel method, using aluminium butoxide as precursor and acetylacetone as chelating agent to stabilize the sol. The dip-coating parameters (sol concentration and withdrawal speed) were optimized in order to get waveguiding films. For a 15 successive layers deposition and a 700°C annealing treatment, waveguiding films of about 900nm thickness were obtained, which have a 1.582 refractive index at 543.5nm. The influence of the annealing temperature was studied in the 100°C to 1100°C range, in order to follow the elimination of the organic compounds and the existence of stresses. IR spectroscopy shows that an annealing temperature of 800°C is necessary for the complete elimination of the OH and C=O groups of the residual organic compounds, which are derived from the chelating agent. In a parallel way, the Al to O atomic ratio tends to the theoretical Al2O3 composition, according to Rutherford Backscattering Spectroscopy results. The stresses in the film were measured by an optical method. Their evolution with annealing temperature is characterized by two regimes, depending on the organic compounds elimination and the crystallization process.