Silica spheres were prepared by the Stober method, and the method of labeling with pyrene, using aminopropylysilane as the linking agent, was optimized. Excimers between particles were formed when high concentrations of label were used. Both surfactant and polyelectrolyte addition were able to cause hoc formation when added to suspensions of the silica, but only the surfactant changed the I-1/I-3 ratio and diminished excimer formation.