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Molecular impurities in the luminescent ZnO nanocrystals

Larisa Grigorjeva 2Witold Łojkowski 1Donats Millers 2Tomasz Strachowski 1

1. Polish Academy of Sciences, High Pressure Research Center (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
2. Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga LV-1063, Latvia


The luminescence of ZnO nanocrystals produced by different methods was studied and compared with luminescene from bulk single crystal. The luminescence observed is rather different for ZnO nanocrystals produced by different methods, however in all studied sets of nanocrystals the luminescence band at 1.9 - 2.2 eV linked to the intrinsic defects as well as exciton related luminescence (at 3.20 - 3.32 eV) was observed.
The IR absorption spectra shown that all ZnO nanocrystals studied contains besides well known OH groups other molecular impurities also, whereas in single crystal content of other molecular impurities is neglible. Different chemical reactions and processing is used by producers of ZnO nanocrystals. The uncontrolled molecular impurities were incorporated in nanocrystals and/or bound at their surfaces during these chemical processes. Therefore different uncontrolled molecular impurities are responsible for different luminescent properties of ZnO nanocrystals and luminescence could be a simple and powerful tool for ZnO nanocrystals purity checking.
The OH line in IR spectra of ZnO nanocrystals is widened if compared with this line in single crystal. This is an evidence that OH in nanocrystals occupieded a number of different positions, possibly the fraction of these positions are on the nanocrystal surface. The other uncontrolled molecular impurities could be incorporated in different positions also. The luminescence study of ZnO nanocrystals shows that in some cases the intrinsic defects of ZnO were blocked by uncontrolled impurities. This is an promissing tool for nanocrystals engineering.


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Presentation: invited oral at E-MRS Fall Meeting 2004, Symposium G, by Larisa Grigorjeva
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-05-05 15:05
Revised:   2009-06-08 12:55