Plasmonic Optical Nonlinearities of Copper Sulfide Nanoparticles
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.91
Plasmonic Optical Nonlinearities of Copper Sulfide Nanoparticles Yasushi Hamanaka1, Tatsunori Hirose1, Kaoru Yamada1, Kazuki Miyagawa1, and Toshihiro Kuzuya2 1
Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan.
2
Muroran Institute of Technology, Mizumoto-cho, Muroran, Hokkaido 050-8585, Japan.
ABSTRACT
Spherical Cu2-xS nanoparticles with an average diameter of 4.6 nm were synthesized by a colloidal method, and their optical nonlinearities around localized surface plasmon resonance in the near-infrared region were investigated. Resonant enhancement of nonlinear absorption, which is similar to that in the case of the noble metal nanoparticles in the visible region, was observed. The nonlinear absorption coefficients of the Cu2-xS nanoparticles were smaller as compared with those of Au nanoparticles with the same dimensions and concentrations. Theoretical simulation of electric field distributions around individual nanoparticles suggested that the free carrier concentration in Cu2-xS nanoparticles was one order of magnitude smaller than that in Au nanoparticles, which led to a weaker local electric field and weaker optical nonlinearity.
INTRODUCTION Localized surface plasmon resonance (LSPR) of heavily doped semiconductor nanoparticles (NPs) has attracted significant attention as a strong candidate for plasmonic devices, which are responsible to near-infrared (NIR) light and possess tunable LSPR frequencies due to carrier doping [1-5]. Plasmonic NPs based on noble metals exhibit strong third-order optical nonlinearities owing to local-field enhancement effect by LSPR excitation in the visible frequency region [6]. Therefore, the NIR-LSPR in plasmonic semiconductor NPs makes them potential candidates for application in all-optical switching devices based on the Kerr-type optical nonlinearity corresponding to optical fiber communications. The third-order nonlinear susceptibility (3) of NP dispersions with the volume fraction of NPs being p can be expressed as follows [7]: | |
,
(1)
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where NP(3) is the third-order susceptibility of the NP and fl is a local-field enhancement factor represented by the following equation: .
(2)
This relation is based on the Maxwell-Garnett theory, where E0 and El are electric fields of the incident light and the local field, respectively; () and m are the dielectric functions of the NP and the surrounding material, respectively [7]. These theoretical expressions indicate that third-order optical nonlinearities of plasmonic NP dispersions are strongly dependent on the effect of local-field enhancement. In this study, we investigated the third-order optical nonlinear properties of Cu2xS NPs, which are some of the best known plasmonic semicon
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