  We study experimentally time-resolved emission of CdSe quantum dots in an
environment with a controlled local density of states (LDOS). The decay rate is
measured versus frequency and as a function of distance to a mirror. We observe
a linear relation between the decay rate and the LDOS, allowing us to determine
the size-dependent quantum efficiency and oscillator strength. We find that the
quantum efficiency decreases with increasing emission energy mostly due to an
increase in nonradiative decay. For the first time, we manage to obtain the
oscillator strength of the important class of CdSe quantum dots. The oscillator
strength varies weakly with frequency in agreement with behavior of quantum
dots in the strong confinement limit. Surprisingly, the measured absolute
values are a factor of 5 below theoretically calculated values. Our results are
relevant for applications of CdSe quantum dots in spontaneous emission control
and cavity quantum electrodynamics.
