Cu doped ZnO nanoparticle sheets

doi:10.1016/j.matchemphys.2010.09.021

Materials Chemistry and Physics

Volume 125, Issues 1–2, 1 January 2011, Pages 263-266

https://doi.org/10.1016/j.matchemphys.2010.09.021 Get rights and content

Abstract

Cu doped ZnO nanoparticle sheets were synthesized via a proposed solution route with mixed Zn(NO₃)₂ and Cu(NO₃)₂ precursors at a low temperature of 95 °C. Scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectrometry results demonstrate that the nanostructues synthesized by solutions with higher Cu(NO₃)₂ concentration are nanoparticle sheets comprised of uniform Cu doped ZnO nanoparticles with diameters around 20 nm. Room-temperature photoluminescence spectra of the nanoparticle sheets show tunable near band emissions centered at 390–405 nm and strong yellow emissions at 585–600 nm. Absorbance spectra show gradual redshift in the UV range with the increase of Cu concentrations in the ZnO nanomaterials. The study provides a simple and efficient route to prepare Cu doped ZnO nanomaterials at low temperature. The as-synthesized products with both violet and yellow emissions are promising for white light-emitting diode applications.

Introduction

Recently, ZnO has attracted much attention owing to its special opto-electrical properties due to its direct wide band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature, which also render ZnO one of the most promising candidates for use in nanodevices. To improve their performance, ZnO-based nanomaterials are doped or alloyed to modulate their electrical and optical properties for optoelectronic applications. Recently, many elements such as Al [1], [2], Mg [3], [4], [5], Co [6], Ni [6], Ga [7], [8], [9], In [9], Sn [9], S [10], and Cu [11], [12], [13] have been doped or alloyed into ZnO and demonstrate tunable properties. Among these, the Cu dopants could modify the luminescence of ZnO crystals by creating localized impurity levels [14]. Additionally, Cu behaving as an acceptor in ZnO crystals makes it a good candidate for creating p-type ZnO [15]. Moreover, Cu doped ZnO nanomaterials or thin films have also been reported as diluted magnetic semiconductors [16], [17], which have attracted much interest due to potential applications in spintronics [18].

However, the previously reported Cu doped ZnO nanomaterials [11], [12], [13] were conventionally synthesized by vapor deposition at high temperatures in the 650–1150 °C range, which constrains the selection of substrates and their opto-electrical applications. Although a low-temperature ion-beam route has been demonstrated to synthesize Cu doped ZnO nanoneedles [16], an expensive ultrahigh vacuum ion beam system is needed. In this work we report on the synthesis and optical properties of Cu doped ZnO nanoparticle sheets produced by a proposed simple, low-cost, and efficient solution method at a low temperature of 95 °C. The composition of the nanoparticle sheets could be adjusted by varying the ratios of Cu²⁺ to Zn²⁺ in the mixed precursors. Room-temperature photoluminescence (PL) spectra show tunable violet and yellow emissions. The study provides a simple route to synthesize Cu doped ZnO nanomaterials at low temperature. The nanomaterials with both violet and yellow emissions are promising for applications in white-light emitting nanodevices.

Section snippets

Experimental

In this work, the synthesis of Cu doped ZnO nanoparticle sheets was performed by putting a Si substrate into a glass bottle filled with an aqueous solution of 0.2 M C₆H₁₂N₄ (HMTA, Sigma, 99.5%) and varied concentrations of cupric nitrate trihydrate (Cu(NO₃)₂·3H₂O, Aldrich, 98–100%) as well as zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O, Aldrich, 98–100%) at 95 °C for 11 h. After the crystal growth, the samples were rinsed with distilled water followed by acetone, and then dried in an oven at 75 °C for 30

Results and discussion

Fig. 1(a) is a low-magnification SEM image of the nanomaterials synthesized using an aqueous solution containing 0.1 M Cu(NO₃)₂ and 0.05 M Zn(NO₃)₂. The nanostructures are composed of numerous nanosheets. From the high-magnification image shown in Fig. 1(b), it is found that the nanosheets consist of nanoparticles with diameters around 20 nm. Fig. 1(c) shows a low-magnification SEM image of the nanostructures synthesized using an aqueous solution containing 0.05 M Cu(NO₃)₂ and 0.1 M Zn(NO₃)₂. The

Conclusion

In this work, Cu doped ZnO nanoparticle sheets were synthesized by a proposed solution route at a low temperature of 95 °C. SEM, TEM, and EDS results demonstrate that the nanosheets are composed of Cu doped ZnO noparticles with a diameter of around 20 nm. With the increase of Cu²⁺ to Zn²⁺ ratios in the Zn²⁺/Cu²⁺ mixed solutions, the Cu concentration in the nanosheets rises. Room-temperature PL measurements show tunable violet and yellow emissions. This study thus provides a simple and efficient

Acknowledgments

This work was supported by Research Grants NSC 98-2221-E-390-013-MY2 and 97-2815-C-390-017-E from the National Science Council of Taiwan. The authors also thank the Center for Micro/Nano Technology Research, National Cheng Kung University, and the Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Taiwan for provision of the HRTEM and PL.

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Cu doped ZnO nanoparticle sheets

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgments

Solid State Electron.

Appl. Surf. Sci.

J. Pharm. Sci.

J. Luminesc.

Appl. Phys. Lett.

Nanotechnology

J. Phys. Chem. B

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.

J. Phys. Chem. B

J. Phys. Chem. B

ACS Nano

J. Phys. Chem. C