Monodisperse fluorescent organic/inorganic composite nanoparticles are synthesized through the spontaneous self-assembly of block copolymer polystyrene-block-poly(vinylpyridine) and rare-earth ions (europium, terbium, thulium, etc.).Depending on the rare-earth ions selected, tunable light-emission colors, including the primary red, green, and blue, are accomplished.Further, by stoichiometric mixing of the nanoparticles that emit different colors, the full color spectrum can be accessed.Both electron microscopy and spectroscopic characterizations confirm specific interactions of rare-earth and block copolymers.The resulting nanoparticles are monodisperse as characterized by dynamic light scattering.They are very stable and can be dispersed in common solvents, and together with homopolymers, they form ordered arrays and thin films (both supported and free-standing) upon solvent evaporation.The resulting nanoparticle thin films exhibit mechanical flexibility for ease of processing or device integration.