  We observe experimentally that ensembles of quantum dots in three-dimensional
(3D) photonic crystals reveal strongly nonexponential time-resolved emission.
These complex emission decay curves are analyzed with a continuous distribution
of decay rates. The log-normal distribution describes the decays well for all
studied lattice parameters. The distribution width is identified with
variations of the radiative emission rates of quantum dots with various
positions and dipole orientations in the unit cell. We find a striking sixfold
change of the width of the distribution by varying the lattice parameter. This
interpretation qualitatively agrees with the calculations of the 3D projected
local density of states. We therefore conclude that fluorescence decay of
ensembles of quantum dots is highly nonexponential to an extent that is
controlled by photonic crystals.
