The radiative lifetime of excited states is governed by Fermi’s Golden Rule. For many applications, the radiative decay rate is an important parameter. For example, for scintillators materials in PET scanners, a short response time is crucial and it has been realized that the d-f emission of Pr3+ is faster than for the widely applied d-f emission from Ce3+. In this paper, the radiative decay rate of d-f emission from Pr3+ is systematically investigated in a wide variety of host lattices, including scintillators materials. The variation in the decay rate is analyzed based on Fermi’s Golden Rule. The trend observed is best described using a full cavity model to correct for local-field effects and a λ3 factor to account for the energy of the transition. Still, there is a considerable scatter of the experimental data around the best fit to these data. The variation is explained by uncertainties in the refractive indices and a variation in the transition dipole moment of the d-f transition for Pr3+. Based on the results, the shortest radiative lifetime that can be achieved for Pr3+ d-f emission is predicted to be ∼6 ns.