A facile route to silver–cadmium sulfide core–shell nanoparticles and their nonlinear optical properties

doi:10.1016/j.matlet.2013.03.137

Materials Letters

Volume 104, 1 August 2013, Pages 76-79

https://doi.org/10.1016/j.matlet.2013.03.137 Get rights and content

Highlights

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Ag@CdS core–shell nanoparticles were synthesized by a reversed micelle method.
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The CSNPs were found to exhibit an obvious nonlinear response at room temperature.
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The refraction index of the CSNPs increase ten times as that of pure CdS NPs.

Abstract

The synthesis of silver–cadmium sulfide core–shell nanoparticles (Ag@CdS CSNPs) with positional and morphological control still remains a challenge because of the large lattice mismatch between the two components. In this paper, Ag@CdS CSNPs with controllable core morphology and shell thickness were synthesized by using a reversed micelle method. Z-scan measurements show that the synthesized CSNPs exhibit an obvious nonlinear response at room temperature. Both the nonlinear absorption coefficient and refraction index of the CSNPs increase tens of times as those of the pure CdS shell counterparts, which result from the large local field enhancement of localized surface plasmon of cubic Ag core.

Introduction

As an important II–VI group semiconductor, CdS has a direct band-gap of 2.5 eV and is probably one of the most important electronic and optoelectronic materials with prominent applications in nonlinear optical devices, light emitting diodes, lasers, etc. [1]. Over the past few years, various CdS-based hetero-nanostructures have attracted considerable interest because the integration of different materials within the same structure can multiple their functionalities and even generate new synergetic properties [2], [3], [4], [5], [6], [7], [8], [9], [10]. For example, nonlinear optical (NLO) properties can be enhanced in several CdS-metal core–shell nanoparticles (CSNPs) as compared to those of the CdS core counterparts [9], owing to the large local field and strong surface plasmon resonant absorption of the metal shell. Metallic core could also have a significant impact on the NLO response of the CdS shells. Okamoto et al. [11] have theoretically shown that an optical switching and optical bistability phenomena of Ag–CdS CSNPs occur due to the change in the refractive index of the CdS shell produced by the localized surface plasmon enhanced third-order nonlinear optical effect of CdS. However, the synthesis of Ag–CdS CSNPs with positional and morphological control still remains a challenge because of the large lattice mismatch between the two components.

In literature [12], the optical properties of Ag nanoparticles were tuned through changing their shape and morphology. Compared with more symmetrically shaped nanospheres, Ag nanocubes possess obvious optical anisotropies which have been proved useful to potential photonic devices [13]. Therefore, Ag–CdS CSNPs synthesized using Ag nanocubes as cores will offer a way to tailor the interactions between the Ag core and the CdS shell of the CSNPs and the functional properties of devices based on them. In this paper, we synthesized Ag@CdS CSNPs by using a reversed micelle method, in which the Ag core has a perfect cubic shape. Z-scan measurements show that the synthesized CSNPs exhibit an obvious nonlinear response at room temperature. Both the nonlinear absorption coefficient and refraction index of the CSNPs increase tens of times as those of the pure CdS shell counterparts.

Section snippets

Experimental

The synthesis of Ag@CdS CSNPs was carried out in two steps: Ag nanocubes were firstly prepared according to Ref. [14], then the CdS shells were coated onto the prepared Ag nanocubes using a reversed micelle method with some modification. Typically, 2 mL of the already-made Ag nanocubes was first diluted in 6 mL cyclohexane. Then 0.2 mL nonionic surfactant Igepal CO-520 was added into the mixture and continuously stirred for 2 h. After that, 0.1 mL of 4 mM Cd(NO₃)₂ water solution was added and the

Results and discussion

Fig. 1a presents the SEM image of a typical sample of silver nanocubes, indicating that a large quantity of Ag particles with good uniformity were achieved using this approach in our work. These silver nanocubes have a mean edge length of 60 nm, with a standard deviation of 10 nm. Their surfaces are smooth, as shown in a typical TEM image in Fig. 1b. The inset in Fig. 1b shows the selected electron diffraction pattern obtained by directing the electron beam perpendicular to one of the square

Conclusions

Ag@CdS core–shell nanoparticles were synthesized by using a reversed micelle method. Z-scan measurements on the CSNPs indicate a large third-order nonlinear response compared with those on pure CdS NPs synthesized under the same conditions, due to the large local field and strong surface plasmon resonance absorption of cubic Ag cores.

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A facile route to silver–cadmium sulfide core–shell nanoparticles and their nonlinear optical properties

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

J Alloys Compd

J Alloys Compd

Nanoscale

J Phys Chem C

J Phys Chem C

Chem Mater

Langmuir

J Appl Phys