Macroscopic models for the radiative relaxation lifetime of luminescent centers embedded in surrounding media

Two macroscopic models for the dependence of the spontaneous emission rate of luminescent ions or nanoparticles embedded in dielectric media of various optical refractive indexes are presented. The available experimental results on the spontaneous emission rate (lifetime) are examined using the two models. A simple criterion for how to choose the proper model for a given system is summarized.