Unusual enhancement of fluorescence and Raman scattering of core-shell nanostructure of polydiacetylene and Ag nanoparticle

•A significantly enhanced Raman scattering was observed in a core-shell type Ag@ polydiacetylene (PDA) blue-phase nanoparticle (NP).•The Raman scattering was decreased dramatically while the PDA shell of Ag@PDA NP undertook a phase transition to a fluorescent red phase.•The fluorescence of PDA shell of the Ag@PDA red-phase NP was enhanced 7-fold in the intensity compared with the PDA red-phase NP.