Plasmon-enhanced fluorescence of CaF₂:Eu²⁺ nanocrystals by Ag nanoparticles

We report plasmon-enhanced fluorescence in Eu²⁺ doped CaF₂ (CaF₂:Eu²⁺) nanocrystals assembled with Ag nanoparticles (NPs) using a simple hydrothermal method. The structure, morphology and composition of the nanocrystals are confirmed by X-ray diffraction (XRD), transmission electron Microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and UV–vis absorption spectrum. Ag nanoparticles are ideal building blocks for plasmonic materials that can exhibit a wide range of unique and potentially useful optical phenomena. Surface plasmon enhancement makes significant contribution to enhance the blue fluorescence emission of CaF₂:Eu²⁺. The enhancement on the Eu emission in visible regions is up to a factor of 12.3-fold. As shown in time-resolved measurements, surface Plasmon Resonance (SPR) can reduce the fluorescence lifetime and increase the quantum yield. Furthermore, with increasing Ag concentration, the fluorescence intensity increases to its maximum and then decreases. - Highlights: • CaF₂: Eu²⁺ nanocrystals assembled with Ag NPs using a simple hydrothermal method. • Surface Plasmon enhancement on the Eu emission is up to a factor of 12.3-fold. • The fluorescence intensity is enhanced with increasing amount of Cit-Ag NPs. • Based on the EPR result, the reduction of Eu³⁺→Eu²⁺ has occurred by Cit-Ag catalyst. • SPR results in an increase in the quantum yield and a decrease in the lifetime.