Clustering of rare-earth dopants in GeAs sulfide glasses was studied by fluorescence spectroscopy of Pr-doped glasses and by EPR measurements of Gd-doped samples. The linewidth of the g ~ 2 resonance of Gd 3 + , as well as the relative intensity of emission from the 1 D 2 level of Pr 3 + , was used as a relative measure of rare-earth clustering. Rare earths were found to have low solubility in uncodoped GeAs sulfide glasses, which also displayed poor fluorescence efficiency due to severe clustering. Codoping such glasses with Ga greatly enhanced rare-earth solubility and dispersal, particularly for Ga:rare earth ratios =< 10:1, as evidenced by the narrower EPR resonances and more intense luminescence of Gd- and Pr-doped glasses, respectively. In, P and Sn were also observed to 'decluster' rare earths, although less efficiently than Ga, whereas codoping with I was found to have no effect on clustering. These phenomena are explained by a structural model in which (1) rare-earth dopants and codopants are spatially associated and (2) rare-earth dispersal is accomplished by a statistical distribution of codopants in tetrahedral network sites.
L'agregation des terres rares dans les verres de sulfures a base de As et Ge a ete etudiee par spectroscopie de fluorescence dans des verres dopes au Pr et par des mesures de RPE d'echantillons dopes au Gd. On a quantifie le phenomene en utilisant la largeur de bande de la resonance de Gd 3 + ainsi que l'intensite relative d'emission a partir du niveau 1 D 2 de Pr 3 + . Les terres rares n'ont qu'une faible solubilite dans les verres Ge-As-S purs, tandis que le codopage avec Ga augmente considerablement la solubilite et l'homogeneite de repartition des terres rares, en particulier pour des rapports Ga/In superieurs a 10. L'incorporation de In, P et Sn favorise aussi la dilution des terres rares dans une moindre mesure que Ga, tandis que l'iode n'a aucun effet sur l'agregation. Un modele structural est propose pour expliquer ces observations.