Effect of Thermal and Mechanical Treatments on the Cathodoluminescence of Tin and Titanium Oxides
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G2.4.1
Effect of Thermal and Mechanical Treatments on the Cathodoluminescence of Tin and Titanium Oxides D. Maestre, R. Plugaru*, A. Cremades and J. Piqueras Departamento de Física de Materiales, Facultad de Ciencias Físicas, Universidad Complutense, 28042, Madrid, Spain * Permanent address: National Institute for R&D in Microtechnologies, IMT-Bucharest, R72996, Romania ABSTRACT The luminescence of titanium oxide and tin oxide has been investigated by cathodoluminescence in the SEM, as a function of the structural changes induced by thermal treatments. The evolution of the luminescence of TiO2 rutile, anatase and mixture phase with the annealing temperature is related to the process of thermal induced grain texture and to transition of metastables phases to the stable rutile. The emission band is peaked at 480 nm for the composite phase and at 580 nm for anatase and rutile phases respectively. A broad band in the 520-560 nm region is present in the spectra of both anatase and rutile phase. Thermal annealing leads to a red shift of the luminescence emission, with the emission band peaked at around 820 nm. In sintered tin oxide the main emission bands appear centered at about 480 nm and 630 nm. The intensity of these bands increases with annealing temperature up to 1200ºC, whereas for samples annealed at 1500ºC these emissions are quenched. Mechanical ball milling has been used to produce nanocrystalline SnO2 grains to investigate the influence of the presence of nanocrystals on the CL emission. INTRODUCTION TiO2 is a detector of reducing gases at high temperatures (800-1000 ºC) whereas a SnO2 sensor operates in the range of temperatures between 100 and 500 ºC due to the different mechanisms responsible for gas sensing [1]. TiO2-SnO2 mixed oxides could give a new class of materials with improved properties for sensors application in a wide range of temperatures [1, 2, 3]. The structure of the oxides and their electrical-optical properties are influenced by interaction with various ambiental factors and especially with the chemical content in the atmosphere [4, 5]. Thin and thick films of tin and titanium oxides have been investigated for oxygen sensing applications [6, 7]. It has been reported that, nanocrystalline structure of the films improves the sensing capability related to surface effects, controlling the electrical properties of the material. In our study, the structure of thick films of tin (SnO2) and titania (TiO2) were investigated in relation with their luminescence behaviour at local scale. The effect of oxygen on structural and phase transitions has been correlated with luminescence emission. EXPERIMENTAL Thick films of the titania phases, rutile (R), anatase (A) and a mixture phase anatase-rutile (nc), were prepared by sintering of powders. The mixture phase shows a nanocrystalline structure, while the grains dimensions of the others phases are of the order of microns.
G2.4.2
Nanocrystalline powders of SnO2 (around 130 nm size) were prepared by mechanical milling of commercial high purity powders. T
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