EN
The spectroscopy of pairs of rare-earth ions is demonstrated for Pr^{3+}:CsCdBr_{3} For reasons of charge compensation only two definite types of Pr^{3+} pairs are formed independent of concentration. Only the pair with the Pr^{3+} ions as direct neighbors shows upconversion. The dynamics of this upconversion process is studied by time-resolved spectroscopy and discussed in the energy level schemes of the single ions, and the pair.