Greatly enhanced Raman scattering and upconversion luminescence of Au-NaYF4 nanocomposites

Novel dual function Au-NaYF4 nanocomposites were prepared by a facile wet chemical method. Hexagonal NaYF4 nanocrystals (NCs) were first produced by a hydrothermal method. Then, these NaYF4 NCs were decorated with gold nanoparticles (NPs) to form hybrid nanostructures. In this dual mode probe, surface enhanced Raman scattering (SERS) and field enhanced fluorescence can be generated independently by using different excitation wavelengths. It was found that the attached gold NPs on the rough surfaces of NaYF4 NCs might generate high density localized electric fields, which could lead to both efficient Raman scattering signal and upconversion (UC) luminescence. The enhancement factors of SERS signals from Au-NaYF4 nanocomposites were investigated using 4-mercaptobenzoic acid. The mechanism of enhanced UC luminescence from the nanocomposites was also discussed based on the population and photoluminescence processes of doped trivalent lanthanide ions. These dual mode nanocomposites may find potential applications in biological detection, imaging, and sensing.