Study of a new europium doped barium/strontium aluminosilicate: structure, fluorescence, phosphorescence and thermoluminescence

At the quest of new white emitting phosphors active in fluorescent and/or phosphorescence modes, the europium doped barium and strontium aluminosilicate (Ba/Sr)_13-xAl_22-2xSi_10+2xO₆₆:Eu phases have been investigated. The first part of this thesis is dedicated to the theoretical background concerning Eu²⁺ luminescence and thermoluminescent (TL) mechanisms. The second part concerns the synthesis routes, the structural characterization and the optical properties of the different studied compositions. Namely, an Eu²⁺ doped compound excited under UV displays two emission bands centred in the blue and the green zone of the visible spectrum, respectively. These ones are associated with Eu²⁺ cations lying at alkaline earth sites with different coordination. Ab-initio calculations based on a DFT approach evidenced the preferential location of Eu at the 9 fold coordinated site. The two emitting bands covers the whole visible spectrum which gives rise to the white luminescence detected with the naked eyes. Changes in the europium content and the Ba/Sr ratio significantly modify the colour rendering of the emission. After stopping the UV excitation, a white long persistent luminescence is observed and lasts about ten minutes. Traps responsible for phosphorescence have been characterized by emission decay measurements concomitantly to TL experiments. Finally, the spectral analyses of the TL signal underlined a dependency of the emitted spectra with the excitation temperature. This surprising phenomenon gave rise to a detailed discussion. (author)