UP-CONVERSION STUDIED BY SELECTIVE TIME RESOLVED EXCITATION TECHNIQUES IN PR3+-LAF3

A strong blue fluorescence was observed following orange-yellow laser excitation in the **1D//2 multiplet of Pr**3** plus :LaF//3. 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 reuslts 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 trnasfer are discussed.