Eu3+ ions as an optical probe to follow the growth of colloidal ZnO nanostructures

The colloidal growth of ZnO exhibits interesting dynamics, which is generally probed using absorbance measurements. Here, we have shown that the sharp luminescent signals from the Eu3+ ions act as a potential luminescent spectral probe to follow the growth of ZnO nanostructures. The Eu3+-doped ZnO nanocrystals were synthesized by a colloidal method. The asymmetry ratio calculated from the Eu3+ emission intensity peaks (D-5(0) -> F-7(2)/D-5(0) -> F-7(1)) gradually decrease with the increase in the size of the ZnO nanostructures. This is attributed to the increase in the surface related defects as the size of the ZnO nanocrystals is increased. The above result is supported by controlling the growth of the ZnO nanocrystals with capping ligands. The Eu3+ luminescence intensity hardly is affected upon ligand capping. Additional experiments such as lifetime measurements and photocatalytic activity of ZnO strongly indicate that Eu3+ can be used as a potential tool to follow the growth of colloidal ZnO nanostructures. We believe the study can be extended to understand the growth mechanism of several other colloidal nanostructures.