Local Field effects on the radiative lifetime of emitters in surrounding   media: virtual- or real-cavity model?
  For emitters embedded in media of various refractive indices, different macroscopic or microscopic theoretical models predict different dependencies of the spontaneous emission lifetime on refractive index. Among those models are the two most promising models: the virtual-cavity model and the real-cavity model. It is a priori not clear which model is more relevant for a given situation. By close analysis of the available experimental results and examining the assumptions underlying the two models, we reach a consistent interpretation of the experimental results and give the criteria which model should apply for a given situation. 
Chang-Kui Duan, Michael F. Reid and Zhongqing Wang