Long-lifetime fluorescence and crystal field calculation in Cr 4+-doped Li2MSiO4, M = Mg, Zn

The diffuse reflectance spectra of Cr:Li2MSiO4, M = Mg, Zn, indicate that in these compounds, chromium ions occur in the 4+, 5+, and 6+ oxidation states simultaneously. Under selective excitation in a Cr 4+ absorption band, a very long fluorescence decay time is observed for both compounds: ∼110 μs at room temperature and ∼300 μs at 30 K. These are by far the longest fluorescence lifetimes reported for Cr 4+ activated materials. In Cr4+:Li2MSiO 4, the 1E excited state level lies below the lowest component of the 3T2 level and the fluorescence decay time is dominated by the long-lifetime 1E level for which the transition to the ground state is spin-forbidden. The reverse situation occurs for the other Cr4+ doped compounds and their fluorescence lifetimes, governed by the short-lifetime 3T2 state, are only a few microseconds. A crystal field calculation, performed for Cr4+:Li 2MSiO4, confirms the above interpretation and supports the localization of Cr4+ at the silicon site in this compound. © 2003 Elsevier B.V. All rights reserved

Lettre de C. Jousseaume à De Bonaventure

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2. -La gestion concertée et décentralisée de l'eau en France

Après avoir rappelé les principales démarches de mise en oeuvre de la politique de l’eau (planification, programmation, contractualisation) et présenté les dispositifs de suivi de cette politique, la contribution ci-après fait état des premiers retours d’expériences qui en résultent, en vue d’une consolidation ou d’une inflexion de ces dispositifs.Jousseaume C., Retkowsky Y. 2. -La gestion concertée et décentralisée de l'eau en France. In: L'école française de l'eau au service du développement mondial. Congrès de la Société Hydrotechnique de France. 25èmes journées de l'hydraulique. Chambéry, du 15 au 18 septembre 1996. Tome 1, 1998

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