Transition from Long-Range to Short-Range Energy Transfer through Donor Migration in Garnet Hosts

We demonstrate that the mechanism for nonradiative energy transfer, a critical aspect in many optical systems, can switch from a longer-range dipole dipole mechanism to a short-range exchange mechanism through energy migration between donors. This transition significantly increases energy transfer rates and is analyzed using measurements of Tb(3+)-((S)D(4))-> Ce(3+)-(5d(1)) energy transfer as a function of Tb(3+) concentration in (Lu,Tb)(3)Al(5)O(12): Ce(3+) garnet phosphors. The additional short-range energy transfer is assigned to exchange by the analysis of the migration and trapping rates as well as estimates of the relevant exchange integrals.