Clustering effects on double energy transfer in heavily ytterbium–erbium-codoped silica fibers

We study clustering effects in heavily ytterbium–erbium-codoped silica fibers. We demonstrate that the fraction of both ions found in clusters can exceed 50% in such fibers. A clustering effect is at the origin of an efficient double energy transfer process that generates a green fluorescence. An original method, based on a dynamic analysis of the ytterbium–erbium system, permits determination of the intracluster transfer rates involved, which are found to be high enough to compensate for the weak metastability of the erbium intermediate level.