Enhancing the Surface-State Emission in Trap-Rich CdS Nanocrystals by Silver Nanoparticles

It is well known that surface plasmon resonance (SPR) can selectively enhance the photoluminescence (PL) from nearby chromophores with a single emission peak at an appropriate distance. Here, we combine white light-emitting CdS quantum dot nanocrystals containing band-edge and surface-state emissions simultaneously with Ag nanoparticles and study the interaction between them. It is found that the surface-state emission is always enhanced while the band-edge emission quenched regardless of the SPR wavelength of Ag nanoparticles. This phenomenon reveals that the SPR of Ag nanoparticles is not enhancing the emission from a wavelength-matched state. We propose that the surface plasmon of Ag nanoparticles is first excited by the energy of the band-edge emission and then the excited energetic electrons transfer to the surface-state of CdS. Through this energy transfer process, the surface-state emission is enhanced and band-edge emission quenched. This investigation can not only deliver understanding of the complicated interaction between metallic nanoparticles and nearby multi-emission-peak contained chromophores, but it also has potential applications in tuning the color temperature of white light-emitting materials.