Aggregation of Rhodamine B (RhB) fluorophore in confined nanoscale domains changes the photoluminescence behavior of RhB in core-shell silica/PGMA-RhB nanoparticles. Under an excitation at 365 nm, silica/PGMA-RhB nanoparticles exhibit a two-band emission of yellow and blue in a tetrahydrofuran (THF) solution, compared to the yellow emission of RhB in a THF solution. The yellow and blue emissions of silica/PGMA-RhB nanoparticles are of approximately equal intensity, and mix together to show white light emission from the core-shell nanoparticles. Removal of the silica core from the core-shell nanoparticles does not alter its photoluminescence behavior. Therefore, the white light emission of RhB in the nanoparticles originates from the aggregation of RhB molecules in a nanoscale domain. This finding provides a new and convenient approach to the preparation of white light photoluminescent materials.