Spontaneous decay of CdSe/ZnS core-shell quantum dots at the air-dielectric interface

We report measurements of the fluorescence decay times of CdSe/ZnS core-shell quantum dots at the air-dielectric interface for several dielectrics with different refractive indices. The results are in agreement with a simple theory that accounts for the impact of the refractive index on the density of states and magnitude of the vacuum field, as well as for the local-field correction inside the quantum dot. The results suggest that, by embedding the quantum dots into a high-index dielectric material, one can reduce the spontaneous decay time to sub-nanosecond scale while preserving high quantum efficiency.