Issue 40, 2015

Nanoparticle shape anisotropy and photoluminescence properties: Europium containing ZnO as a Model Case


The precise control over electronic and optical properties of semiconductor (SC) materials is pivotal for a number of important applications like in optoelectronics, photocatalysis or in medicine. It is well known that the incorporation of heteroelements (doping as a classical case) is a powerful method for adjusting and enhancing the functionality of semiconductors. Independent from that, there already has been a tremendous progress regarding the synthesis of differently sized and shaped SC nanoparticles, and quantum-size effects are well documented experimentally and theoretically. Whereas size and shape control of nanoparticles work fairly well for the pure compounds, the presence of a heteroelement is problematic because the impurities interfere strongly with bottom up approaches applied for the synthesis of such particles, and effects are even stronger, when the heteroelement is aimed to be incorporated into the target lattice for chemical doping. Therefore, realizing coincident shape control of nanoparticle colloids and their doping still pose major difficulties. Due to a special mechanism of the emulsion based synthesis method presented here, involving a gelation of emulsion droplets prior to crystallization of shape-anisotropic ZnO nanoparticles, heteroelements can be effectively entrapped inside the lattice. Different nanocrystal shapes such as nanorods, -prisms, -plates, and -spheres can be obtained, determined by the use of certain emulsification agents. The degree of morphologic alterations depends on the type of incorporated heteroelement Mn+, concentration, and it seems that some shapes are more tolerant against doping than others. Focus was then set on the incorporation of Eu3+ inside the ZnO particles, and it was shown that nanocrystal shape and aspect ratios could be adjusted while maintaining a fixed dopant level. Special PL properties could be observed implying energy transfer from ZnO excited near its band-gap (3.3 eV) to the Eu3+ states mediated by defect luminescence of the nanoparticles. Indications for an influence of shape on photoluminescence (PL) properties were found. Finally, rod-like Eu@ZnO colloids were used as tracers to investigate their uptake into biological samples like HeLa cells. The PL was sufficient for identifying green and red emission under visible light excitation.

Graphical abstract: Nanoparticle shape anisotropy and photoluminescence properties: Europium containing ZnO as a Model Case

Supplementary files

Article information

Article type
20 Apr 2015
19 Sep 2015
First published
22 Sep 2015
This article is Open Access
Creative Commons BY license

Nanoscale, 2015,7, 16969-16982

Author version available

Nanoparticle shape anisotropy and photoluminescence properties: Europium containing ZnO as a Model Case

M. Gerigk, P. Ehrenreich, M. R. Wagner, I. Wimmer, J. S. Reparaz, C. M. Sotomayor Torres, L. Schmidt-Mende and S. Polarz, Nanoscale, 2015, 7, 16969 DOI: 10.1039/C5NR02550H

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