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Open Access item Vitrocerámicos transparentes del sistema SiO2-Al2O3-Na2O-K2O-LaF3/YF3: Mecanismos de cristalización y propiedades ópticas
|Authors:||Pablos Martín, Araceli de|
|Advisor:||Pascual, M. J.|
|Publisher:||Universidad Autónoma de Madrid|
|Abstract:||Rare-earth (RE) doped oxyfluoride glass-ceramics possess interesting
optical properties with applications in telecommunications and optoelectronics.
These materials combine the transparency and mechanical and chemical
resistance of aluminosilicate glasses with the low phonon energy and facile
incorporation of RE ions in the fluoride crystals. The incorporation of RE ions
in the crystalline phases enhances the optical emission intensity, a major
property of these materials.
Nanocrystallization in four different oxyfluoride glasses in the system SiO2-
Al2O3-Na2O-K2O-LaF3/YF3 has been studied. Heat treatments above the glass
transition temperature give rise to the devitrification of different crystalline
phases, depending on the composition: LaF3, NaLaF4, KLaF4 and NaYF4.
Crystalline fraction and crystal size are dependent on the time and temperature
of thermal treatment.
Thermal and structural characterisation has been studied using several
techniques, including viscosity, dilatometry, X-ray and neutron diffraction,
quantitative Rietveld refinement, transmission electron microscopy techniques
(EELS, EFTEM, Simulations), differential scanning calorimetry (DSC), 27Al, 19F
and 23Na NMR, and EXAFS.
The crystallization mechanism is shown to occur via regions of La- and Siphase
separation in the glass, from which the fluoride crystals develop during
heat treatment. The interface between the glass matrix and the crystals in the
demixed ranges is enriched in network formers, mainly SiO2, creating a viscous
barrier, which inhibits further crystal growth and limits the crystal size to the
The influence of the addition of RE ions (Tm3+, Eu3+, Yb3+, Er3+) on nanocrystallisation
has been analysed. The optical characterisation of the RE-doped
glasses and glass-ceramics has been performed, mainly focussed on confirming
the distribution of RE ions between glassy matrix and crystals, and on the upconversion
(UC) emission processes (doping with Tm3+ provides an up UC
emission in the blue region (450-480 nm) from excitation in the NIR (790 nm)),
and the differences between glasses and glass-ceramics.
Finally, preliminary results of the production of waveguides through ionic
exchange and their characterisation (optical modes, attenuation of light during
propagation along the guide, stress profile) will be shown|
|Appears in Collections:||(ICV) Tesis|
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