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Title: Critical shell thickness and emission enhancement of NaYF 4:Yb,Er/NaYF4/silica core/shell/shell nanoparticles
Authors: Qian, L.P.
Yuan, D. 
Yi, G.S. 
Chow, G.M. 
Issue Date: Dec-2009
Citation: Qian, L.P., Yuan, D., Yi, G.S., Chow, G.M. (2009-12). Critical shell thickness and emission enhancement of NaYF 4:Yb,Er/NaYF4/silica core/shell/shell nanoparticles. Journal of Materials Research 24 (12) : 3559-3568. ScholarBank@NUS Repository.
Abstract: Amorphous silica shells, used for functionalization of inorganic nanoparticles in bioapplications, were coated on chemically synthesized NaYF4:Yb,Er upconversion fluorescent nanoparticles via a reverse microemulsion method by using dual surfactants of polyoxyethylene (5) nonylphenylether and 1-hexanol, and tetraethyl orthosilicate as precursor. NaYF4: Yb,Er nanoparticles were equiaxed with a particle size of 11.1 ± 1.3 nm. The thickness of silica shell was ∼8 nm. NaYF 4:Yb,Er/silica core/shell nanoparticles were well dispersed in solvents such as ethanol and deionized water. The emission intensities of NaYF4: Yb,Er/silica core/shell nanoparticles remained the same as that of uncoated nanoparticles after surface functionalization with an amine group using (3-aminopropyl)-trimethoxysilan. Silica, although providing a good barrier to the nonradiative relaxation between the upconversion nanoparticles and the environments, did not enhance the emission intensity of upconversion nanoparticles. To increase the emission intensity of NaYF4: Yb,Er/silica core/shell nanoparticles, an undoped NaYF4 shell (∼3-nm thick) was deposited on the upconversion nanoparticles before the silica coating. The total emission intensity of NaYF4: Yb,Er/NaYF4silica core/shell/shell nanoparticles increased by 15 times compared to that without the intermediate NaYF4 shell. The critical shell thickness of NaYF4 was ∼3 nm, beyond which no further emission intensity enhancement was observed. © 2009 Materials Research Society.
Source Title: Journal of Materials Research
ISSN: 08842914
DOI: 10.1557/jmr.2009.0432
Appears in Collections:Staff Publications

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