  Colour centres in diamond are promising candidates as a platform for quantum
technologies and biomedical imaging based on spins and/or photons. Controlling
the emission properties of colour centres in diamond is a key requirement for
developing efficient single photon sources with high collection efficiency. A
number of groups have produced enhancement in the emission rate over narrow
wavelength ranges by coupling single emitters in nanodiamond crystals to
resonant electromagnetic structures. Here we characterise in detail the
spontaneous emission rates of nitrogen-vacancy centres positioned in various
locations on a structured substrate. We show an average factor of 1.5
enhancement of the total emission rate when nanodiamonds are on an opal
photonic crystal surface, and observe changes in the lifetime distribution. We
present a model to explain these observations and associate the lifetime
properties with dipole orientation and polarization effects.
