Towards rare-earth clustering control in doped glasses

Tn this paper, the basic limitation for optical amplifiers linked with the existence of the so-called clustering of rare-earth (RE) ions is addressed. Clusters of RE dopant are related both to what could be called "interaction clusters" and to "chemical clusters". Such interaction clusters do not depend on the chemical processes of the glass preparation and cannot be reduced through it. However, the existence of chemical clusters of spatial extension of a few Angstrom can tremendously increase ion-ion interactions of all kinds. The physical process of co-operative luminescence is closely related to chemical clustering. Using this effect with Yb3+ as a probing ion, clear signatures of RE clusters can be obtained for different glass compositions and RE concentrations. Developing this approach, a new doping principle is proposed. It is based on the recognition that introducing the doping RE into the glass composition through given precursor crystals with large RE-RE distances, allows some control of the clustering of RE ions and of their self-quenching. So even after complete melting of the precursor and independently of the final glass composition the glass is shown to keep some memory of the doping procedure. (C) 2001 Elsevier Science B.V. All rights reserved.