Luminescent properties of the potassium zinc phosphates of composition K1−xTlxZn(PO3)3
Résumé
Crystalline and glassy K1−xTlxZn(PO3)3 polyphosphates have been synthesized and characterized. UV–visible spectroscopy was systematically used in order to analyze the optical properties of Tl+ ions both in crystalline and glassy forms with the similar compositions. The investigated polyphosphates can be considered as a model system since the spectroscopic properties of Tl+ ions in the glasses could be deduced by comparison with those in crystals. From structural point of view, in the crystalline forms the thallium ions are six-fold coordinated in a dissymmetrical oxygenated sites. Three luminescences (α, AX, AT) have been then observed and were attributed to the isolated Tl+ ions. In the glassy forms, an additional luminescence (D) has been detected in the low-energy range and was assigned to the Tl+ pairs formation. The relationship between the Tl+ site symmetry and its optical properties is discussed in the context of the Fukuda's model.