Spontaneous emission in nanoscopic media: Rayleigh scattering of vacuum fluctuations

Summary form only given. Over more than three decades many experiments have shown that the rate of spontaneous emission from an emitter can be strongly modified due to its electromagnetic surrounding. It is also well-known that the fluorescence lifetime of an emitter changes when embedded in dielectric media where aside from a change in the density of states, it is influenced by the local fields in the dielectric. The goal of our work has been to study the transition between the regime of an emitter in vacuum to that of a bulk dielectric medium, emphasizing the domain where the emitter´s environment has a subwavelength extent. In our experiment we have investigated the dependence of the spontaneous emission rate of Eu/sup 3+/ ions in polymer nanospheres of different diameters, ranging from 20nm to 2000nm. In order to perform well-defined control experiments, we have combined atomic force microscopy and fluorescence confocal microscopy to make measurements only on isolated single spheres lying on a glass substrate.