Strong blue fluorescence-with a quantum yield over 80 % (see figure)of ultrastable (ZnO)polymer core-shell nanoparticles is suggested to arise by a luminescence mechanism different from that for conventional ZnO nanoparticles. The stable particles are produced by methacrylic-group-modified ZnO nanoparticles reacting with liquid monomers, the polymerization being initiated by free radicals pre-existing oil the ZnO nanoparticle surfaces.