The present invention is directed to controlling aggregation of rare earth particles using block copolymers and rare earth base particles. More particularly, invention is also directed to forming stable complexes of rare earth aggregates by complexing rare earth base particles with oppositely charged-neutral di-block copolymers. Even more particularly, invention is also directed to forming stable complexes of rare earth nanoparticles by complexing rare earth ultrafine particles with oppositely charged-neutral di-block copolymers.