Well-defined organic composite nanoparticles were prepared from perylene bisimide dye and silicon-cored fluoranthene derivate molecules. The composite nanoparticles exhibited good stability and thermal properties. The fluorescence emission of the perylene bisimide dye can be efficiently enhanced in composite nanoparticles based on efficient Föster resonant energy transfer. The composite nanoparticles exhibited tunable emission colors from blue to red by changing the concentration of the perylene bisimide dye. White-light emission with CIE coordinates (0.327, 0.339) was obtained as a good candidate for applications in white optoelectronic devices.