We report the synthesis of silica nanoparticles and microspheres doped with Pr3- and Era. Acetic acid is used to catalyze the hydrolysis and condensation of tetraethyl orthosilicate in the presence of LnCl(3), 6H(2)O. The particles are spherical and discrete with particle sizes and size distributions controllable by variation of the reactant concentrations and reaction tithe. The relative standard deviation of particle diameters can be as low as 10%. The particles exhibit bright room-temperature luminescence when excited by an argon ion laser at 488 nm.