Sm(DBM)3phen-doped polymer optical fibers were prepared by thermal polymerization. The cross relaxation model of
clustering Sm3+ ions was described, and the cluster in this kind of fibers was studied based on the above model. The
percentages of clustering ions in different fibers were obtained by the rate equation combining with fiber transmission
experiment. While rare-earth-doped concentrations in these fibers are 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000
ppm and 10000 ppm, the percentages of clustering ions are 0.05, 0.05, 0.05, 0.05, 0.06, and 0.07, respectively. The result
shows that this kind of fibers has low percentage of clustering ions. With the increasing of Sm3+ concentration, the
percentage of clustering ions hardly increases, the clustering of Sm3+ ions is not obvious.