beta-NaYF4:Yb,Er@SiO2@Ag core-shell hybrid nanostructures are prepared and single core-shell hybrid particle is taken to investigate the influence of separation layer on the metal enhanced upconversion luminescence and corresponding mechanism. It is found that the green (S-4(3/2) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) emissions of Er3+ increase first and then decrease with the increase of silica shell thickness. The best enhancement is observed at the silica thickness of 12 nm. Time-resolved spectra study shows that the emission enhancement dominates when the silica thickness is 12 nm, which leads to an enhancement factor of 1.28. But the enhancement factor reduces to 0.52 when the silica shell thickness is 5 nm. Here, we define enhancement factor g(omega F) as g(omega F) = I-F/I-0, IF and I-0 are fluorescence intensities of UCNPs with emission enhancement and without plasmon enhancement. The luminescence enhancement is owing to the enhanced emission process rather than the excitation process. (C) 2016 Published by Elsevier Ltd.