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. 2011 Jun 17;4(6):1132-1143.
doi: 10.3390/ma4061132.

Optical Properties of ZnO Nanoparticles Capped With Polymers

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Free PMC article

Optical Properties of ZnO Nanoparticles Capped With Polymers

Shingo Tachikawa et al. Materials (Basel). .
Free PMC article

Abstract

Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the addition of the polymer to the ZnO nanoparticle solution, the optical properties were drastically changed. When PEG was added to the solution before the synthesis of ZnO nanoparticles, the fluorescence intensity increased. At the same time, the total particle size increased, which indicated that PEG molecules had capped the ZnO nanoparticles. The capping led to surface passivation, which increased fluorescence intensity. However, when PEG was added to the solution after the synthesis of ZnO nanoparticles, the fluorescence and particle size did not change. When PVP was added to the solution before the synthesis of ZnO nanoparticles, aggregation of nanoparticles occurred. When PVP was added to the solution after the synthesis of ZnO nanoparticles, fluorescence and particle size increased. This improvement of optical properties is advantageous to the practical usage of ZnO nanoparticles, such as bioimaging.

Keywords: capping; fluorescence; nanoparticle; polyethylene glycol; polyvinyl pyrrolidone; zinc oxide.

Figures

Figure 1
Figure 1
XRD pattern of the synthesized nanoparticles.
Figure 2
Figure 2
TEM image of the ZnO nanoparticles: (a) ZnO nanoparticles without PEG (PEG/Zn2+ = 0.0[mol/mol]); (b) ZnO nanoparticles with PEG (PEG/Zn2+ = 1.2[mol/mol]).
Figure 3
Figure 3
Absorption spectra of the ZnO nanoparticle solution. (a) PEG was added to the solution; (b) PVP was added to the solution. Black dotted line: polymer was not added to the solution. Red solid line: polymer was added before the synthesis of ZnO nanoparticles. Blue solid line: polymer was added after synthesis. Brown solid line: data of only polymer solution.
Figure 4
Figure 4
PL spectra of the ZnO nanoparticle solution with an excitation wavelength of 300 nm: (a) PEG was added to the solution; (b) PVP was added to the solution. Black dotted line: polymer was not added to the solution. Red solid line: polymer was added before the synthesis of ZnO nanoparticles. Blue solid line: polymer was added after the synthesis. Brown solid line: data of only the polymer solution.
Figure 5
Figure 5
PLE spectra of ZnO nanoparticle solution with an emission wavelength of 500 nm: (a) PEG was added to the solution; (b) PVP was added to the solution. Black dotted line: polymer was not added to the solution. Red solid line: polymer was added before the synthesis of ZnO nanoparticles. Blue solid line: polymer was added after the synthesis of ZnO nanoparticles.
Figure 6
Figure 6
Schematic of ZnO nanoparticles capped by polymer molecules: (a) PEG was added to the ZnO solution before synthesis; (b) PEG was added to the ZnO solution after synthesis; (c) PVP was added to the ZnO solution before synthesis; (d) PVP was added to the ZnO solution after synthesis.

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