Enhancement of the YAG:Ce,Yb down-conversion emission by plasmon resonance in Ag nanoparticles

Abstract

Silver (Ag) plasmonic structures on the surface of Сe and Yb co-doped yttrium aluminium garnet fluorescent epitaxial films were prepared by the magnetron sputtering technique. The nucleation and growth of Ag nanoparticles (NPs) were controlled by a thermal annealing process. Annealing of the samples at T ≥ 350 °C results in growth of Ag NPs size. A broad absorption band peaking in the range from 440 to 550 nm was observed due to the dipole mode of the surface plasmon resonance (SPR) of Ag NPs. Photoluminescence emission and excitation spectra were measured for samples having different concentrations, sizes and shapes of Ag particles. Plasmon-enhanced Ce3+ luminescence was observed for samples with particles bigger than 50 nm. On the other hand luminescence quenching was observed for samples with high Ag concentration and smaller NPs size. Presented luminescence results suggest that there are two competitive effects, namely enhancement and quenching, affecting the luminescence in the presence of Ag NPs. The enhancement of Ce3+ luminescence is mainly attributed to local field effect i.e. the SPR of Ag NPs causes an intensified electromagnetic field around them, resulting in enhanced optical transitions of Ce3+ ions in the vicinity of Ag NPs. The quenching effect, in the presence of Ag NPs, suggests an energy transfer from Ce3+ ions directly to them. The competition between the plasmonic enhancement and the quenching effect is discussed for samples with different nanoparticles concentrations and sizes.