Preparation and enhanced off-resonance optical nonlinearities of CdS-capped gold nanoparticles embedded in BaTiO 3 thin

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Ye Liu Physics Department, National Key Laboratory of Applied Surface Physics, Fudan University, Shanghai, People’s Republic of China (Received 11 March 2002; accepted 29 July 2002)

A simple approach has been developed for the synthesis of Au@CdS core-shell nanoparticles by a direct self-assembling process. Stable Au@CdS composite colloids were prepared by thiourea, as a double-functional reagent that acted as the linkage agent between Cd2+ ions and gold nanoparticles. The CdS-capped gold composite nanoparticles were successfully integrated into BaTiO3 films. A significant enhancement of third-order nonlinear optical susceptibility in the Au@CdS nanoparticles with core-shell structure is reported. To compare the effect of enhanced nonlinear response, single gold or CdS nanoparticles embedded in BaTiO3 films were also prepared.

I. INTRODUCTION

Nonlinear optical materials have attracted increasing interest over the past 20 years, due to the numerous applications in various fields such as telecommunications, optical data storage, and information processing.1–3 Semiconductor and metal nanocrystallites have been studied extensively because of their larger third-order nonlinear susceptibilities and ultrafast nonlinear optical response.4–7 Nanoparticles like CdS, CdSxSe1−x, PbS, Cu, and Au,8–15 embedded in glass or polymer have been reported to exhibit enhanced third-order nonlinearities, which present large possibility for the application in nonlinear optical devices such as optical computing, real time holography, optical correlators, and conjugators. The semiconductor–metal core-shell nanoparticles (CSNs) suspended in a nonlinear medium should exhibit strongly enhanced nonlinear response by several orders of magnitude higher than their single components proposed by several authors, including Neeves and Birnboim from theoretical calculations.16,17 Recently, Honma et al.18 claimed to have synthesized silver colloidal particles surrounded by the shell of CdS. Chen et al.19 also reported to have prepared Au@CdS core-shell nanoparticles by assembling the preformed monodisperse CdS and Au nanoparticles into hybrid particles, based on the electrostatic interaction between the amine-covered CdS and thiocarboxylate-covered gold nanoparticles. a)

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J. Mater. Res., Vol. 17, No. 11, Nov 2002 Downloaded: 04 May 2015

However, there were seldom related reports20–22 about their nonlinear properties reasonably available to verify Neeves’ theoretical predictions in these papers. In addition, the nonlinear materials had better be integrated into existing structures such as films and fibers for practical applications in optical switching and amplification. However, there were seldom reports about core-shell composite nanoparticles fabricated into films. Several methods have been employed to prepare coreshell structural materials, including surface precipitation reaction,23,24 surface reaction,25 and self-assembly;26–28 some pro