2014 Ce travail présente des résultats expérimentaux montrant, pour la première fois, un transfert à l'intérieur d'une paire d'ions à la suite d'une excitation sélective par un laser pulsé. Ce transfert est étudié avec Pr3+ : LaF3 en mesurant la dynamique d'une fluorescence de up-conversion. Les résultats montrent que deux mécanismes doivent être invoqués, selon la distance qui sépare les deux ions de chaque paire, pour expliquer les taux de transfert mesurés sur 11 paires différentes. Abstract. 2014 Experimental results are reported which show for the first time a transfer inside pairs of ions after their selective excitation by a pulsed laser. This transfer is studied in Pr3+ : LaF3 by monitoring the time dependence of an up-conversion fluorescence. The results show that two mechanisms must be considered, depending upon the distance between the ions of the pairs, to explain the transfer rates measured on 11 different pairs.
A strong blue fluorescence has been observed following orange-yellow laser excitation in the 1D2 multiplet of Pr3+ : LaF3. This blue fluorescence has different time evolution depending on the excitation wavelength within the absorption line. Time resolved excitation techniques have been used to study this time evolution. It is shown that satellite lines, which accompany the main line, are due to ions between which energy transfer is very active. A mechanism is proposed for the observed up-conversion which is in good agreement both with our results and with observations reported by others. The nature of the interaction between the ions of the satellite lines and that of the interaction responsible for the energy transfer are discussed
In Nd3+ -doped CsCdBr 3 crystals, most of the Nd3+ ions form pairs. A detailed analysis of the optical spectroscopy of these pairs has been carried out using both absorption and luminescence spectra. Due to the low value of the Debye cutoff frequency for the phonons, many excited.1evels are luminescent, thus giving a lot of spectroscopic information and allowing the assignment of 65 levels to their associated irreducible representations. These results have been used to deduce, through a fitting procedure, the free-ion and crystal-field parameters. The results are discussed and compared with those found in other compounds.
Direct measurement of fluorescence quenching rates for various Pr 3+ pairs in weakly doped LaF3 are reported. Since few pairs only are quenched, the transfer mechanism is short range. From the rate values, the shape of the fluorescence decay for heavily doped samples is predicted. The good agreement with the observed decay proves the interest of the connection between microscopic and macroscopic measurements. Finally arguments are developed to prove that the transfer mechanism is superexchange
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