Poly(ether ether ketone) (PEEK) was used to prepare a sulfonated terbium salt (Tb-SPEEK). This salt emits green fluorescent light under u.v. excitation. The fluorescence originates from the transition of the 5D4 level of Tb3+ to the levels of F-7(J) (J = 6, 5, 4, 3). The fluorescence intensity increases with increasing Tb content, reaching a maximum value at around 9 wt% Tb, and then decreases due to the formation of ionic aggregates in the salt. The excitation of the salt is related to its Tb content and corresponding solid state, and changes after experiencing thermal treatment.