The long-afterglow phosphor SrAl2O4 : Eu2+, Dy3+ is liable to hydrolyze in water with deterioration of its luminescent properties. In this study, in situ emulsion polymerization was first used to prepare phosphor coated with poly(methyl methacrylate-co-butyl acrylate) [P(MMA-co-BA)] to improve water resistance. Fourier transform infrared spectra suggested that the polymer attached to the phosphor by chemical bonding. Observation by scanning electron microscopy (SEM) showed that a polymer layer formed on the surface of the phosphor. The resistance to water of the phosphor coated with the polymer layer was much better than that of the uncoated phosphor because the transparent polymer layer could suppress its hydrolysis process. Low-density poly-ethylene (LDPE) plastics, doped with long-afterglow phosphors, were manufactured with an extrusion technique. Through coating with P(MMA-co-BA), the compatibility of phosphor with the LDPE matrix was improved, as determined by SEM. The luminous LDPE plastics blended with the phosphor coated with polymer showed long and strong phosphorescence with little loss of persistence phosphorescence compared to the uncoated phosphor. The LDPE plastics still retained their mechanical properties through doping with 3% (mass fraction) of the phosphors. (c) 2008 Wiley Periodicals, Inc. j Appl Polym Sci 109:3811-3816,2008