Efficient upconversion fluorescence in NaYF4:Yb3+, Er3+/mNaYF4 multilayer core-shell nanoparticles

Here, we show a core-shell nanostructure which effectively improves NIR-to-visible upconversion quantum efficiency and luminescence intensity. The NaYF 4 :Yb 3+ , Er 3+ /mNaYF 4 (m = 0, 1, 2, 3, 4, 5) core-shell nanoparticles are synthesized using a thermal decomposition method. The structure, morphology and fluorescence spectrum of the nanoparticles are confirmed by XRD , TEM and fluorometer. The average size of the as-prepared NaYF 4 :Yb 3+ , Er 3+ /mNaYF 4 cores is about 8 nm while the thickness of the shells varies from 0.5 nm to 8 nm for different m values. With 980 nm excitation, the nanoparticles exhibit distinct emission peaks at 522 nm, 544 nm and 650 nm. It is noticed that an increasing shell thickness enhances their fluorescence intensity . The fluorescence lifetime and quantum yield of obtained multilayer NaYF 4 :Yb 3+ , Er 3+ /mNaYF 4 nanoparticles are also discussed.