Upconversion luminescence with tunable lifetime in NaYF4:Yb,Er nanocrystals: role of nanocrystal size

• DOI: 10.1039/c2nr32482b
• Publication Date: 2012-11-12T18:03:35Z
• Authors: Jiangbo Zhao; Zhenda Lu; Yadong Yin; Christopher McRae; James A. Piper; Judith M. Dawes; Dayong Jin; Ewa M. Goldys
• Keywords: Photon Upconversion

Despite recent achievements to reduce surface quenching in NaYF(4):Yb,Er nanocrystals, a complete understanding of how the nanocrystal size affects brightness upconversion luminescence is still incomplete. Here we investigated Yb,Er-doped nanocrystals broad range sizes from 6 nm 45 (cubic or hexagonal phases), displaying an increasing red-to-green intensity ratio and reduced lifetimes with decreasing size. By analyzing process set rate equations, found that their asymptotic analytic solutions explain lower decay rates red compared green luminescence. Furthermore, quantified effect on lifetime model where emitters are divided between near-surface inside regions each nanocrystal. We clarify influence four nonradiative recombination mechanisms (intrinsic phonon modes, vibration energy ligands, solvent-mediated quenching, defects) for different-size find defect density dominates small (below 15 nm) nanocrystals. Our results indicate defect-reduction strategy key step producing increased variety bioimaging biosensing applications.