Papers by Michel Aegerter
All solid state electrochromic devices have potential applications in architectural and automotiv... more All solid state electrochromic devices have potential applications in architectural and automotive fields to regulate the transmission and reflection of radiant energy. We present the optical and electrochemical characteristics of two solid state windows having the configuration glass/ITO/TiO2-CeO2/TiO2/TiO2-CeO2/ITO/glass and glass/ITO/WOa/TiO2/TiO2-CeO2/ITO/glass where the three internal layers have been prepared by sol gel methods. The preparation of the individual sols and some physical properties of the different sol gel coatings are reported.
Quim Nova, 1998
Recebido em 2/12/96; aceito em 18/4/97 CARACTERIZATION OF Nb 2 O 5 THIN FILMS WITH ELECTROCHROMIC... more Recebido em 2/12/96; aceito em 18/4/97 CARACTERIZATION OF Nb 2 O 5 THIN FILMS WITH ELECTROCHROMIC PROPERTIES. The sols for thin electrochromic coatings of Nb 2 O 5 were obtained by synthesis of the niobium butoxide from BuONa and NbCl 5 . The ~300nm thick films were deposited by dip-coating technique from the alkoxide solution and calcined at 560 o C in O 2 atmosphere during 3 hours. The particles size of niobium oxide (V) powder (~20µ µ µ µ µm) was obtained from x-ray diffraction using the Scherrer equation. The coatings were characterized by cyclic voltammetry and cronoamperommetry techniques. The spectral variation of the optical transmittance were determined in situ as a function of the cyclical potencial and memory effect. The insertion process of lithium is reversible and change the film color from transparent (T=80%) to dark blue (T=20%).
The sol-gel process is an interesting alternative to produce gels, ceramics, glasses, thin films ... more The sol-gel process is an interesting alternative to produce gels, ceramics, glasses, thin films and fibres which are difficult to prepare or could not be prepared by conventional methods. This technique is an excellent preparative route to synthesize materials such as zirconium phosphate through hydrolysis and polycondensation reactions of metal alkoxide. We have used the sol-gel method with application of ultrasound in the preparation of a-Zr(HPO4)2I-I20 gels. This material was initially known as an inorganic ion exchanger and was of interest as a solid state electrolyte for use in fuel cell and alternative energy sources . The electrical transport property of o~-Zr(HPO4)2H20 is due to diffusion of protons along the hydrated surface of their microcrystalline structure, and depends essentially on the number of surface ionogenic groups [7], particle dimensions [8] and their hydration .
Electrochim Acta, 2001
Coatings of pure and Zr, Sn, Li, Ti and Mo doped niobium pentoxide have been prepared by the sol–... more Coatings of pure and Zr, Sn, Li, Ti and Mo doped niobium pentoxide have been prepared by the sol–gel process and deposited on ITO-coated glass using the dip coating technique. Their structure, morphology and electrochromic (EC) properties have been studied. The coatings are transparent and, depending on the nature and amount of the doping and the sintering temperature, they present a brown, gray or blue color after Li insertion. The EC properties of 4×8 cm2 size coatings, tested up to 5000 cycles, are highly stable with a coloration efficiency measured at 550 nm ranging between 16 and 28 cm2/C. Same size devices have been built with the configuration glass/FTO/pure or doped Nb2O5/liquid electrolyte/TiO2–CeO2/FTO/glass. In agreement with a theoretical estimation and with this choice of counterelectrode (IS), only Nb2O5:0.4 Mo coatings could be considered. For a fixed thickness (180 nm) of the IS electrode, the transmittance response of the device was found to increase with the thickness of the EC layer. The maximum change of the photopic transmission was 0.3 with an Li+ charge exchange of 18 mC/cm2. The devices were stable up to about 15,000 potentiostatic cycles performed between ±2.5 V, 120 s.
In this work we present result on the preparation of planar waveguides based on HfO2 and HfO2-SiO... more In this work we present result on the preparation of planar waveguides based on HfO2 and HfO2-SiO$2). Stable sols containing europium and erbium doped HfO2 nanoparticles have been prepared and characterized. The nanosized sol was either deposited on quartz substrates or embedded in (3-glycidoxipropil)trimethoxisilane used as a hybrid host for posterior deposition. The refractive index dispersion and luminescence characteristics were determined for the resulting HfO2 films. The optical parameters of the waveguides such as refractive index, thickness and propagation losses were measured for the hybrid composite. The planar waveguides present thickness of a few micra and support well confined propagating modes.
ZrO 2 coatings for corrosion protection were deposited on 304 stainless steel by sol-gel method u... more ZrO 2 coatings for corrosion protection were deposited on 304 stainless steel by sol-gel method using zirconium propoxide as precursor and densified in air and in oxygen-free (argon or nitrogen) atmospheres. XRD and IR data of the films were practically independent of the atmosphere used in the densification step showing that the ceramic oxide is properly formed from the precursor. The corrosion behavior of the stainless steel substrate was studied by potentiodynamic polarization curves in the absence and the presence of ZrO 2 coatings prepared in air, argon or nitrogen. The coatings extended the lifetime of the material by a factor of almost eight in a very aggressive environment, independently of the preparation procedure. The possibility of depositing pure or mixed oxide films by sol-gel methods in the absence of additional oxygen will allow the preparation of specific coatings onto oxygen-reactive substrates.
Phys Status Solidi B Basic So, 1971
A quantitative analysis of the higher transitions of the M center in the UV up to 5.0 eV in KC1 c... more A quantitative analysis of the higher transitions of the M center in the UV up to 5.0 eV in KC1 crystals with high [MI : [F] ratio and unaligned and aligned M centers shows several new excitations ("LM bands"). Assuming that the LM excitation leads to conductive states, a simple electron kinetic model shows that UV irradiation of the F + M center system produces ionized F and M centers (a and Fi) while competing capture processes partially destroyed them or form F and M centers. The F; center production spectrum should closely follow the absorption ratio of LM:LF while the bleaching spectrum should follow the F' and M spectrum. Experimental confirmation of this model is presented. By X-raying the crystal (containing F + M centers) at LHeT, extra electron traps are introduced into the crystal and shift the equilibrium of the reaction to higher amount of I?; center, which are not stabilized by F' and M centers. These extra F; centers anneal out near 40'K in parallelity with the third stage annealing of X-ray produced a-centers-interstititala anions. L'analyse quantitative des transitions optiques du centre M dans I'dtraviolet jusqu' A 5 eV dens des cristaux de KC1 ayant un rapport de concentration [M]:[F] BevB et des centres M non alignb ou alignb montre la p r h n c e de plusieurs nouvelles bandes d'absorption (bandes Ly). En supposant que l'excitation optique de ces dernihres conduisent B des Btab photoconducteurs, un modhle de cinbtique Blectronique simple montre que l'irradiation UV des centres F et M produit des centres F et M ionisBs (centres a et Fl), tandis que des processus compbtitifs de capture lea dbtruisent partiellement ou crbnt des centres F' et M . Le spectre de production des centres F : devrait alolg suivre celui du rapport des constantes d'absorption K(Lh1) :R(LF) tandis que le spectre de blanchiment optique s'identifierait 8 U X spectres F' et M'. Une confirmation experimentale de ce modele est prhentb. L'irradiation X d'un cristal (ayant prbalablement des centres F et M) 8. la tempbrature de I'hBlium liquide introduit des trappes Blectroniques supplbmentaires. L'Bquilibre de lo rbaction est alors dbplac6 vers de plus grandes concentrations de centres Fa+ qui ne sont plus stabilieb par des centres F' et M . Les centres F; supplbmentaires s'annihilent au voisinage de 40 O K en parallblisme avec le 3eme stade d'annihilation des paires de Frenkel crBhs par rayons X (centre a-anions interstitiels).
Journal of Physics C Solid State Physics, 1980
ABSTRACT
Coatings were obtained on borosilicate glass and fused silica substrates with thicknesses of up t... more Coatings were obtained on borosilicate glass and fused silica substrates with thicknesses of up to 230 nm from solutions with compositions along the Zn Sn O tie line. The preparation of the sols was accomplished by combinatorial chemistry with a robotic sample processor using different Zn II , Sn II and Sn IV salts and alkoxides, as well as salts of different doping agents (e.g. Sb V , Ta V , In III ) dissolved in various solvents and additives. The films were made by spin-coating followed by a thermal treatment in air, inert or reducing atmosphere at temperatures up to 1000 • C. Except for a few cases, mixed crystalline phases of ZnO, SnO 2 and ZnSnO 3 or Zn 2 SnO 4 are usually observed within the range 0.4 < [Zn]/([Zn] + [Sn]) < 0.75. Pure Zn 2 SnO 4 and ZnSnO 3 coatings exhibit good optical properties with a haze <0.2% and a transmission in the visible range >85%. In contrast to literature, results obtained for similar coatings by sputtering and pulsed laser deposition, all the sol-gel coatings showed a high resistivity of ρ > 3 cm even after a forming gas treatment and/or doping.
We have observed ultraviolet upconversion fluorescence from the 4 D 3/2 and 2 P 3/2 levels of Nd ... more We have observed ultraviolet upconversion fluorescence from the 4 D 3/2 and 2 P 3/2 levels of Nd 3ϩ in fluoroindate glass under infrared pumping. It was found that the excitation of a large population in the 4 F 3/2 metastable level allows to achieve strong upconversion emissions at 354 and 382 nm. A simple rate equation model reproduces the temporal behavior of the upconverted emission and allows us to estimate the energy transfer rate among three Nd 3ϩ ions participating in the process.
T, L/nirersiti' oj Utah, Sal/ Lake ('/0, Utah 84/12, (5.4 The absorption and emissjall properties... more T, L/nirersiti' oj Utah, Sal/ Lake ('/0, Utah 84/12, (5.4 The absorption and emissjall properties al F 2 centers in KCI(two adjacent anion vacancies which hind one electron) were investigated between 0.6 and 5eV using an optically aligned center system. Energy positions, level degeneracies, polarization behavior and oscillator strengths of 8 absorption transitions were found in close agreement to the calculated states of the H2 molecular ion corrected for a single dielectric constant and the proper separation between the two effective positive charges. Excitation of the lowest 2pe~state at 1.38 /1111 leads with temperature independent quantum efficiency to a Stokes shifted emission at 1.67 am almost in mirror symmetry with the zero phonon line at 1.5260 nm. Excitation of all higher absorption transitions (2p~T,etc.) at liquid helium temperature (LHeT) produces a visible luminescence at 600 nm. At higher temperature a thermally activated process (activation energy IE t).063 eV) transfers the excitation energy to the lowest excited state 2pa~quenching the 600 nm luminescence and producing the JR emission.
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Papers by Michel Aegerter