The preparation of spherical phosphor (Y2O3:Eu) particles that are monosized for a given set of conditions, are described. The nature of the resulting self-assembled and close packed phosphor spherical particles appears to be very promising for both field emission devices (FED) and high definition television (HDTV). The size of the particles can be controlled by careful manipulation of the experimental conditions, the rationale behind this is discussed. The luminescent efficiency of the particles as a function of particle size it, also reported. It is demonstrated that good light output is possible from nanocrystals.