The luminescence efficiency of lanthanide-doped upconversion nanoparticles is of particular importance for their embodiment in biophotonic and photonic applications. Here, we show that the upconversion luminescence of typically used NaYF 4:Yb 3+30%/Tm 3+0.5% nanoparticles can be enhanced by ~240 times through a hierarchical active core/active shell/inert shell (NaYF 4:Yb 3+30%/Tm 3+0.5%)/NaYbF 4/NaYF 4 design, which involves the use of directed energy migration in the second active shell layer. The resulting active core/active shell/inert shell nanoparticles are determined to be about 11 times brighter than that of well-investigated (NaYF 4:Yb 3+30%/Tm 3+0.5%)/NaYF 4 active core/inert shell nanoparticles when excited at ~980 nm. The strategy for enhanced upconversion in Yb 3+/Tm 3+-codoped NaYF 4 nanoparticles through directed energy migration might have implications for other types of lanthanide-doped upconversion nanoparticles.
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