XPS and UV–vis studies of Ga-doped zinc oxide nanoparticles synthesized by gelatin based sol-gel approach

doi:10.1016/j.ceramint.2016.05.155

Ceramics International

Volume 42, Issue 12, September 2016, Pages 13605-13611

https://doi.org/10.1016/j.ceramint.2016.05.155 Get rights and content

Abstract

Undoped and gallium-doped ZnO nanoparticles, (ZnO NPs) (Zn_1−xGa_xO, x=0.0, 0.03, 0.06, 0.09, 0.12, 0.15), were synthesized by a gelatin-based, sol–gel method. Structural and morphological studies of the resulting products were carried out via X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The XRD results revealed that the sample products were crystalline with a hexagonal wurtzite phase. Furthermore, the TEM images indicated ZnO NPs having approximately spherical shapes, with their particle size distributed over the nanometer range. The XRD and TEM results also showed a decrease in crystallite and particle sizes of NPs from x=0.0 to 0.15. The size-strain plot (SSP) method was employed to study the individual contributions of crystallite sizes and lattice strain to the peak broadening of the undoped and doped ZnO NPs. The effect of doping on the optical band-gap and crystalline quality was also investigated, using ultraviolet-visible (UV–vis), X-ray photoluminescence (XPS), and spectroscopies of the pure and doped ZnO NPs. It was observed that the band-gap and O-vacancies of the doped ZnO NPs were red-shifted in comparison with those of the undoped ZnO NPs in UV–vis and XPS results.

Introduction

Zinc oxide (ZnO) is a well-known material due to its promising applications in optoelectronic, light emission, solar cells, and transparent conducting oxides [1], [2], [3], [4]. ZnO has been recognized as a photonic material, especially in the ultraviolet (UV) region, owing to its appropriate energy band-pap of 3.2 eV and large excition bonding energy of 60 MeV [5]. Doping of ZnO with a wide variety of ions is a way to change its properties in order to meet the demands of several application fields. Among these various dopants, the transition metals such as iron (Fe), cobalt (Co), nickel (Ni), and chromium (Cr) have been doped to ZnO so as to obtain dilute magnetic materials [6], [7]. ZnO naturally shows an n-type behavior due to the presence of defect, but some dopants are utilized to enhance this property [8]. According to the literature, aluminium (Al), gallium (Ga), and indium (In) are found to be the most suitable dopants to improve n-type properties of ZnO [9], [10]. Lithium (Li), sodium (Na), and potassium (K) have been applied as dopants to prepare p-type material [11], [12]. Moreover, the optical, structural, biological, and electrical properties of ZnO can be controlled by doping elements [13], [14], [15], [16], [17], [18], [19], [20], [21]. ZnO structures with diverse morphologies have been discovered to possess many practical applications in micro- and nano-devices. Based on the required morphologies of nanocrystalline ZnO, the number of synthesis methods has been developed, including sol-gel [22], solvothermal [23], hydrothermal [24], sonochemical [25], precipitation [26], and chemical vapor deposition (CVD) [27]. Among these methods, sol-gel is known as the method responsible for synthesis of pure and doped ZnO NPs and nanopowders in large-scale production [28].

In the present research, Ga-doped ZnO NPs were synthesized by so-gel method using gelatin as a natural polymerization agent. Ga was utilized in order to control the size and energy band-gap of the ZnO NPs. The optical properties of the prepared NPs were studied as Ga concentrations in ZnO matrix.

Section snippets

Materials and methods

Zinc nitrate hexahydrate [Zn(NO₃)₂6H₂O], gallium nitrate [Ga(NO₃)₃], and gelatin [type B obtained from bovine skin] were used as precursor materials and distilled water as the solvent. The precursor materials were purchased from Sigma-Aldrich and were deployed without further purifications. The stoichiometry of the elements was calculated according to Zn_1−xGa_xO [x=0.0 (ZnO), 0.03 (ZG3), 0.06 (ZG6), 0.09 (ZG9), 0.12 (ZG12), 0.15 (ZG15)] so as to prepare six compounds, including pure and doped

Results and discussion

Fig. 1 shows DSC curves obtained from ZnO and ZG15 gels. There is an endothermic peak at 100 °C and 110 °C for ZG15 and ZnO, respectively, which is attributed to the evaporation of water. The sharp exothermic peaks detected around 180 °C for both samples are related to the decomposition of organic group of gelatin chains. These reactions are accompanied by the release of a large quantity of heat and gas. The pyrocholor phases start to form after 300 °C. Consequently, the crystallization into

Conclusion

Zn_1−xGa_xO nanoparticles were synthesized by sol-gel method in which gelatin was utilized as the polymerization agent. The gels prepared were calcined at 600 °C that was obtained from TGA results. XRD results also indicated that the samples were crystalized in a hexagonal structure. The crystallite size of the Zn_1−xGa_xO was calculated to range from 21.8 to 12.2 nm for x=0.0–0.15. TEM observations demonstrated that the particle size of Zn_1−xGa_xO samples increased from 29 to 13 nm for x=0.0–0.15. In

Acknowledgements

This work was partially funded by Universiti Teknologi Malaysia and Malaysia Ministry of Higher Education through various research grants.

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XPS and UV–vis studies of Ga-doped zinc oxide nanoparticles synthesized by gelatin based sol-gel approach

Abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Conclusion

Acknowledgements

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