Influence of SiO ₂ layer thickness on plasmon enhanced upconversion in hybrid Ag/SiO ₂ /NaYF ₄ :Yb, Er, Gd structures

We report enhanced up-conversion (UC) photoluminescence (PL) in Ag nanoparticles/SiO ₂ /NaYF ₄ : Yb, Er, Gd film sandwiched structures. The effect of SiO ₂ layer thickness on the up-converting optical properties in the sandwiched system was investigated. The UC emission enhancement shows a pronounced distance dependence for the silica spacer layer thickness below 20 nm. The UC emission spectrum of the hybrid structured sample shows a continuous increase in intensity as the thickness of the SiO ₂ layer increases from 0 nm to 15 nm, but displays a quick decrease when the thickness of the SiO ₂ layer increases further from 15 nm. Time-resolved photoluminescence spectroscopy reveals that the fluorescence lifetimes are reduced both for green and red emissions. PL spectroscopy and excitation power studies also show that Ag nanoparticles modified the UC process in this sandwiched structure. We demonstrate switching between PL quenching and enhancement by varying the silica interface thickness. This approach allows us to perform a quantitative analysis of the effect of a metal on the UC nanorods PL intensity.