Conclusion
Irrespective of the alkali base used to promote the hydrolysis of zinc oxide precursor, nucleation and growth of ZnO Q-dots occur by the fast conversion of the zinc oxy-acetate in ZnO nanocrystal. The efficiency of this conversion follows the base strength sequence. Then, after a short transient period, the reaction of ZnO colloid formation achieves a steady state chemical equilibrium between these two species, and the growth of colloidal nanocrystal occurs by the oriented attachment induced by grain-rotation that results in the coalescence of ZnO Q-dots. At the advanced stage the ZnO Q-dots growth occurs by the coarsening governed by the Ostwald ripening process. All these steps, from growth to coalescence and coarsening, are dependent on the alkali base nature and follows a good correlation with the base strength sequence, KOH > NaOH > LiOH. Irrespectively of the nanocrystal growth mechanism, the ZnO Q-dot prepared from LiOH and NaOH present radius smaller than that obtained from the KOH hydrolyzing agent. It evidences that the ZnO Q-dot size and the photoluminescence properties can be finely tuned by the choice of the alkali base nature and of the nominal hydrolysis ratio.
Acknowledgements
The authors want to thank SOLEIL for providing beamtime at the SAMBA beamline and chemistry laboratories and for financial support of the experiments. B.L.C thanks Dr. Sergio Luis Scarpari (IQ/UNESP) for the PL measurements. This work was also partially supported by the FAPESP, CNPq and CAPES/COFECUB cooperation program