For emitters embedded in media of various refractive indices, different theoretical models predict substantially different dependencies of the spontaneous emission lifetime on the refractive index. It has been claimed that various measurements of 4f -> 4f radiative lifetimes of Eu3+ in hosts with variable refractive index appear to favor the real-cavity model [D. Toptygin, J. Fluoresc. 13 (2003) 201 and references therein; G.M. Kumar, D.N. Rao, Phys. Rev. Lett. 91(2003) 203903]. The 5d -> 4f radiative transition of rare-earth ions are dominated by allowed electric dipole transitions with line strengths less perturbed by the ligands. These transitions therefore serve as a better test of the different models. We analyze the lifetimes of the 5d -> 4f transition of Ce3+ in hosts of refractive indices varying from 1.4 to 2.2. The results favor the macroscopic virtual-cavity model based on the Lorentz local field [D. Toptygin, J. Fluoresc. 13 (2003) 201]. (c) 2005 Elsevier B.V. All rights reserved.