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

Abstract

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 (⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁) 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.