Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 114, Issue 21, Pages 9651-9658Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp101324a
Keywords
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Funding
- National Nature Science Foundation of China [50872071, 50972079]
- Shandong Natural Science Fund [JQ200915]
- Nature Science Foundation of Shandong Province [Y2007F03, Y2008F26]
- Foundation of Outstanding Young Scientists in Shandong Province [2006BS04030]
- Tai Shan Scholar Foundation of Shandong Province
- Gong Guan Foundation of Shandong Province [2008GG10003019]
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To get a real understanding on the complexity of origin and mechanism of visible emission for ZnO quantum dots (QDs), we systematically property of visible emission of ZnO QDs with tunable diameters in a range of 2.2-7.8 nm synthesized via a sol-gel route using self-made zinc-oleate complex as a precursor. It is indicated that the visible emission of ZnO QDs can be ascribed to singly ionized oxygen vacancies, which is associated with the paramagnetic centers with electron paramagnetic resonance (EPR) value of g = 2.0056. The visible emission property of the ZnO QDs displays highly size-dependent behavior. With ZnO QDs size decreasing, the visible emission peaks blue-shift to the positions with shorter wavelength due to quantum size effect, however, is different from that of band gap. Quantitative investigation shows that the visible emission can correspond to a transition of holes from the valence band to the preexisting deep donor energy level, which is different from the well-known conclusion that the visible emission is due to the transition of an electron from the conduction band to a deep trap. Two important points can be obtained: the defects of singly ionized oxygen vacancies determine the origin and intensity of visible emission of ZnO QDs; and the visible emission peak position of ZnO QDs is decided by their size, and a transition of holes from the valence band to the preexisting deep donor energy level is responsible for the visible emission of the ZnO QDs,
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