Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study
1 School of Electrical and Electronic Engineering, Nanyang Technological University (NTU), Block S2, Nanyang Avenue, Singapore 639798, Singapore
2 CINTRA, CNRS-NTU-Thales UMI 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore 637553, Singapore
3 Laboratory for Nanotechnology, Instrumentation and Optics (LNIO), University of Technology of Troyes (UTT), 12 rue Marie Curie, Troyes 10000, France
Nanoscale Research Letters 2013, 8:517 doi:10.1186/1556-276X-8-517Published: 6 December 2013
We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix.