Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 113, Issue 11, Pages 4413-4418Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp810275t
Keywords
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Funding
- National Nature Science Foundation of China [10834006, 10774141]
- MOST of China [2006CB601104, 2006AA03A138]
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The synthesis and upconversion luminescence properties upon a 980 nm pump of cubic Lu1.88Yb0.1Er0.02O3 nanocrystals with various shapes, e.g., nanorods, nanosheets, and nanoparticles, are studied. It is observed that with decreasing size of the nanocrystals, the relative intensity of the upconverted red emission (Er3+ : F-4(9/2) -> I-4(15/2)) to the green one (Er3+: (H-2(11/2), S-4(3/2)) -> I-4(15/2)) is increased, and a three-photon process involved in the green upconversion, as described by F-4(9/2) (Er) + F-2(5/2) (Yb) -> H-2(9/2) (Er) + F-2(7/2) (Yb), is synchronously enhanced. An analysis based on steady-state rate equations indicates that the results can be induced by a large I-4(11/2) -> I-4(13/2) nonradiative relaxation rate with a small F-4(9/2) -> I-4(9/2) nonradiative relaxation rate. The large I-4(11/2) -> I-4(13/2) nonradiative relaxation rate is attributed to the occurrence of efficient cross energy transfer to OH- surface group due to the good energy match. As the size of the nanocrystals decreases, the relative surface area is increased, increasing the number of OH- group that can attach to the surface, therefore, enhancing the I-4(11/2) -> I-4(13/2) nonradiative relaxation rate through cross energy transfer to OH- surface group.
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