Polymer encapsulation of yttrium oxysulfide phosphorescent particles via miniemulsion polymerization

Yttrium oxysulfide upconverting phosphor particles can absorb infrared light and emit dopant-dependent visible phosphorescence. This unique optical property has been used for particle-based immunoassay applications. In this study, upconverting phosphor particles were encapsulated with a functionalized polymer (carboxylated polystyrene) shell layer via several approaches, which included the following: (1) the physical adsorption of the carboxylated polystyrene polymer onto the phosphor surfaces, (2) the miniemulsification of the preformed carboxylated polystyrene in a solvent in the presence of the phosphor particles and the subsequent stripping off of the solvent, and (3) the miniemulsification and miniemulsion copolymerization of styrene and methacrylic acid in the presence of the phosphor particles with hexadecane as a costabilizer in combination with a surfactant (sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium dihexyl sulfosuccinate). Miniemulsion technology proved to be the most effective method for forming a functionalized polymeric nanoshell surrounding the phosphor particles. The morphology of the encapsulated phosphor particles was found to vary from symmetric core-shell (i.e., a uniform nanoshell layer with varying shell thicknesses), asymmetric core-shell, dumbbell-like, or raspberry-like partial encapsulation to multiparticle encapsulation. The amount of multiparticle encapsulation could be reduced by the postaddition of a surfactant, but it could not be eliminated completely. (c) 2006 Wiley Periodicals, Inc.