Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study

Kantisara Pita,Christophe Couteau,Pierre Baudin,Quang Vinh Vu,Roy Aad,Gilles Lérondel

doi:10.1186/1556-276x-8-517

Kantisara Pita, Christophe Couteau + Show 4 more

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https://doi.org/10.1186/1556-276x-8-517

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Abstract

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.

Highlights

ZnO nanocrystals (ZnO-NCs) have attracted a lot of interests because of their promising applications in optoelectronic devices, such as light-emitting devices or UV photodetectors [1,2]
Transmission electron microscopy (TEM) of ZnO nanocrystals embedded in SiO2 matrix As mentioned in the ‘Introduction,’ in order to study the formation and evolution of ZnO-NCs in a SiO2 matrix at various annealing temperatures and environments, we have employed the TEM technique and analysis
By looking at the effect of such annealing conditions using TEM images and PL spectra, we identify the best annealing temperature for maximizing the near-UV emission of the ZnO nanocrystals

Summary

Introduction

ZnO nanocrystals (ZnO-NCs) have attracted a lot of interests because of their promising applications in optoelectronic devices, such as light-emitting devices or UV photodetectors [1,2]. In order to facilitate the energy transfer, the emission band from the excited ZnO must overlap with the absorption band of the rare earth ions. A complete investigation on the growth of ZnO-NCs as a function of annealing temperature under different annealing environments is essential to understand the influence of various annealing conditions on the optical properties of ZnO-NC:SiO2 systems. Through this understanding, the emission of ZnO-NCs can be engineered to provide optimum energy transfer to rare earth ions as mentioned above. We report in this article the study on optical and structural properties of ZnO nanocrystals embedded in SiO2 matrix using the low-cost sol–gel technique. Such a result is in agreement with earlier-reported blueshifted transmission spectra observed for ZnO-NCs but diluted in solution, not in thin films [16]

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