Radiation curable compositions, such as UV curable ink compositions, contain a polymeric dispersant, a curable material, that includes a carrier and at least one nanoscale fluorescent pigment particle and an optional non-fluorescent colorant. The fluorescent organic nanoparticle composition includes one or more fluorescent dyes dispersed in a polymeric matrix obtained by modified EA latex process or by emulsion polymerization. In a different embodiment, the nanoscale fluorescent pigment particle composition includes pigment molecules with at least one functional moiety, and a sterically bulky stabilizer compound including at least one functional group, the functional moiety of the pigment associates non-covalently with the functional group of the stabilizer, and the presence of the associated stabilizer limits the extent of particle growth and aggregation, to afford nanoscale-sized pigment particles.