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We have fabricated a CdS-coated Ag nanoparticle using the reverse micelle method and observed the nonlinear optical response of the scattered light intensity caused by an individual particle. In addition, we succeeded in obtaining the complex third-order nonlinear susceptibility χ(3) spectrum near the energy band edge of the CdS film by comparing the experimental result and the result of the Mie calculation that considered the optical Kerr effect of the CdS. At ħωi = 2.43 eV, the χ(3) of the CdS was (1.1 + i0.6) × 10−17m2/V2. We conjecture that an increase in the carriers in the interband transition of the CdS originates from the increase in the χ(3) of the CdS at ħωi > 2.4eV.
©2013 Optical Society of America
1. Introduction
Localized surface plasmons (LSPs), which are excited by metallic nanosized microstructures, have attracted considerable attention as an important phenomenon for the progress of optical nanotechnology. The main characteristics of LSPs are the localization of optical energy near the metal surfaces and the enhancing effect of the electromagnetic field intensity [1,2]. These characteristics were utilized for the probe of the high-resolution near-field optical microscope and the surface enhanced Raman scattering, etc [3,4]. The LSP resonance energy varies with the shape, dimensions, and environment of the metallic nanostructures. Sensors that detect the refractive index change around the metallic nanostructures based on the changes in the LSP resonance characteristics have been employed in a variety of applications [5–7]. As is evident, the use of LSP is a multidisciplinary research endeavor. It is hoped that using LSP would allow nonlinear optical phenomena, which usually occur for intense light, to be triggered locally even with low levels of input power.
CdS is a II –VI semiconductor. Bulk CdS has a melting point of 1600°C [8] and band gap Eg = 2.42 eV [9] at room temperature and normal pressure. This compound semiconductor is known to have a large optical nonlinearity [10–14]. A composite film including CdS nanoparticles was reported to have a large optical nonlinearity when subject to high-speed light pulses [15–20]. The composite film that disperses the core shell particles, i.e., the CdS-coated Au nanoparticles, to the dielectric has also been researched; this film was found to have a third-order nonlinear susceptibility that was larger than that of the composite film of the Au or CdS particle [21]. Moreover, it was reported that the composite film of the core-shell CdS/Ag2S particle had a big two-photon absorption coefficient in the infrared wavelength region [22]. Since the nanoparticle is composed of such a metal and the optical Kerr material shows a large nonlinear optical effect compared with the bulk material, it is expected that the nanoparticle could become a useful nonlinear optical material. In the case of a metallic nanoparticle is coated with the optical Kerr material, the near-field optical power is enhanced by the LSP excitation; further, the refractive index of the optical Kerr material changes with low input power. As a result, the LSP resonance energy experiences a shift. Therefore, the nonlinear optical response is expected to occur even in the case of only a single particle. However, the observed example of nonlinear optical phenomena and nonlinear susceptibility of metallic nanoparticles, coated by an optical Kerr material, has thus far been restricted to composite films of many particles, and hence, the nonlinear optical response of only one particle has not yet been established.
Thus far, we have been researching the nonlinear optical response of one isolated metallic nanoparticle coated with an optical Kerr material. A Mie theory calculation technique that incorporates the optical Kerr effect was developed [23], and the nonlinear optical response of one CdS-coated Ag particle was simulated [24]. It was found that the near-field light intensity on the surface of one core shell particle responded nonlinearly to changes in the incident light intensity. It was reported that the occurrence of the optical switch and the optical bistability phenomenon was possible depending on the size of the core shell structure. A CdS-coated Ag particle with a diameter of several tens of nanometers was fabricated using the reversed micelle method [25]. Moreover, the Rayleigh scattering light from one particle was observed using a dark-field microscopy/spectroscopy optical system, and the nonlinear optical response of the scattered light intensity to the incident light with a pulse duration of 3 ns was examined. Changes in the scattered light intensity resembling those of an optical switch were observed in our sample at an incident light peak power density of 3.3 kW/mm2. However, when the particle was irradiated by the optical pulse for a long time, it was occasionally destroyed. Next, we observed the nonlinear optical response of one particle to the incident light with a pulse duration at the subpicosecond level (220 fs) [26]. For incident light with photon energy higher than about 2.4 eV, which corresponds to the band-gap energy of the CdS, the normalized scattered light intensity reduced with the increase in the incident light intensity. In addition, it was found that the nonlinear optical phenomena were high-speed phenomena caused by one shot with a 220 fs pulse duration. On the other hand, the nonlinear optical response hardly appeared for the pure CdS particulate measured under the same condition. This difference suggests an enhancement of the optical nonlinearity of CdS by the LSP excitation in the CdS-coated Ag particle. In [26], it was argued that the cause of the observed nonlinear phenomenon was the two-photon absorption that resulted from the interband transition of the CdS, since the normalized scattered light intensity reduced with the increase in the incident light intensity. However, the origin of the nonlinear phenomenon was not clear. It is expected that the origin of nonlinear optical phenomena observed on the CdS-coated Ag particle can be understood if the complex third-order nonlinear susceptibility of CdS can be obtained.
The first aim of this study was to obtain the complex third-order nonlinear susceptibility spectrum of the CdS coat film from the experimental results of the nonlinear optical phenomena observed on a single CdS-coated Ag particle. Further, the second aim was to investigate the origin of the nonlinear optical phenomena obtained in the obtained complex third-order nonlinear susceptibility spectrum of the CdS-coated Ag particle.
2. Experimental details
2.1 Materials
The CdS-coated Ag particles were synthesized using the reverse micelle method. An Ag particle was first made in a reverse micelle structure by mixing the non-ionic surfactant Igepal® CO-520, cyclohexane, and AgNO3 water solution at room temperature. In order to make the reductive reaction stable and make the size of Ag particles as identical as possible, we kept the mixture in a glass cell for one week. Next, by synthesizing the CdS in a limited space on the micelle, we obtained CdS grown onto the circumference of the Ag particles. A microemulsion of 0.5 ml was moved to the glass cell, and it was diluted by 1.5 ml cyclohexane. A Cd(NO3)2 water solution (0.01 M) of 4 μl was then added to this. This microemulsion solution was left undisturbed after stirring. After one day, a Na2S water solution (0.01 M) of 4 μl was added to the solution, and it was again left undisturbed for one day after stirring. The microemulsion was then placed on a glass slide, and the CdS-coated Ag particles were heated to 623 K for 30 min to remove the surfactant.
2.2 Linear and nonlinear optical measurement setups
Figure 1 shows the experimental setup for observing the linear and nonlinear optical responses of a single CdS-coated Ag nanoparticle. The object lens for the dark field microscope had a magnification of 100x. The particle was subjected to white light with a numerical aperture (NA) larger than 0.9, and the scattered light (NA ≤ 0.9) formed an image in the confocal plane. A light beam with a 100 μm diameter, obtained from this projected image, was routed to a multichannel spectrometer via an optical fiber. Owing to the effect of the 100x lens, the area of detection on the glass substrate was confined to a diameter of 1 μm. This necessitated the CdS-coated Ag nanoparticles to be separated by a minimum distance of 1 μm in order toinclude only one particle in the detection area. The light spectra were measured using multichannel spectrometers. A xenon lamp was used for the white light source. The dark-field spectra from the CdS-coated Ag particle and away from it are denoted by IS and IB, respectively; and the spectrum of the incident white light is denoted by IRef. The scattered light spectrum of the particle from which the background noise is removed and the bias of the incident light spectrum is corrected can be expressed as
Here, IS-L denotes the scattered light spectrum of the CdS-coated Ag particle in the linear optical response regime.
Fig. 1 Schematic of the experimental setup for measuring the linear and nonlinear optical responses of a single CdS-coated Ag nanoparticle.
A tunable optical parametric amplification (OPA) system comprising a Ti:sapphire oscillator and a regenerative amplifier was used as the light source for observing the nonlinear optical response. The s-polarized fourth harmonic of the OPA idler (repetition rate: 1 kHz, pulse width: 220 fs at the sample position) was incident from the BK-7 glass prism side to the particle. The angle of incidence was approximately 45°, and the incident light was completely reflected at the glass-air interface. The scattered light intensities were measured 10 times under the respective experimental conditions and then averaged. The intensities were measured at an exposure time of 5 s in an energy range of 50 meV, comparable to the incident photon energy ħω. The scattered light intensity from the isolated particle when irradiated by an incident pulse with the peak power density of Ii-peak is denoted by IS-NL. All the measurements were carried out at room temperature.
3. Calculation method
3.1 Linear scattered light spectra
We adopted a spherical model of the CdS-coated Ag particle (see Fig. 2). The scattering cross section spectrum Csca of the linear optical response was calculated on the basis of the general Mie theory. The polarization of the incident light was assumed to be in the x direction. The radius of the Ag core and the thickness of CdS layer are denoted by a and d, respectively. As is well known, the dielectric function of metal spheres depends upon their sizes when the sphere size becomes smaller than the electron mean free path. The complex relative permittivity of Ag particle was calculated by using the expression developed by Kreibig and Vollmer [27] that considered the dependency of the particle size [24]. In this calculation, the values from [28] was used for the complex relative permittivity of bulk Ag. The values from [29] was used for the linear complex relative permittivity of CdS. In our experiment, the LSP characteristic is influenced by both the air and glass refractive indices since the CdS-coated Ag particle is on a glass substrate. Curry et al. [30] report that with the effective refractive index around the silver nanoparticles on a substrate given by neff = α ∙ nmedium + (1–α) nsubstrate, the best fit between the experimental result and the Mie theory value is obtained for a weighting factor α of 0.58. We assumed that the surroundings of our particles can be treated similarly and, hence, obtained a neff value of 1.22 with the refractive indices of the air and the substrate assumed as 1.00 and 1.52, respectively.
3.2 Nonlinear near field enhancement
The incident light intensity dependency on the near-field light intensity on the surface of the CdS-coated Ag particle was calculated using Mie theory with consideration of the optical Kerr effect. The computational model is shown in Fig. 2. The calculation procedure was similar to that presented in [23]. The complex relative permittivity of the CdS, including the optical Kerr effect, is given by
Here, εl is the linear complex relative permittivity of the CdS [29], χ(3)CdS ( = Re{χ(3)CdS} + i Im{χ(3)CdS}) is the complex third-order nonlinear susceptibility of CdS, and ER(r) is the radial component of the local electric field at a distance r from the center of the particle. Equation (2) indicates that the complex relative permittivity at an arbitrary point in the CdS depends on the local light intensity at that point.The electric field ENF on the surface of the CdS in the x-direction as seen from the center of the CdS-coated Ag particle (the red dot in Fig. 2) and the incident light electric field Ei were calculated, and from these, the near-field enhancement factor ηNF = |ENF/Ei|2 was obtained.
4. Results and discussion
4.1 Evaluation of linear scattered light characteristic of CdS-coated Ag particle
The scattered light spectrum of a metallic particle smaller than the wavelength at which the LSP is excited is sensitive to the size of the particle and the dielectric constant inside and outside it. Therefore, it is expected that the size of each particle can be specified by analyzing its scattered light spectrum. In this paper, it was assumed that particles A, B, and C in [26] were core-shell type particles, as in Fig. 2. The diameter of the CdS-coated Ag particle is given by 2(a + d). The diameter of Particle B was measured from scanning electron microscopy (SEM) images. In addition, a and d were chosen such that the peak photon energies of the calculated scattering cross-section spectrum Csca and the measured scattered light spectrum IS-L were in agreement. Accordingly, a and d for particle B were obtained to be 10.0 and 8.0 nm, respectively. Figure 3 shows the result for IS-L and Csca. As shown in the figure, the scales of IS-L and Csca were associated.
Fig. 3 Experimentally obtained linear scattering spectra IS-L and calculated scattering cross section Csca of the CdS-coated Ag particles. The squares, circles, and triangles indicate IS-L and the solid lines indicate Csca.
On the other hand, the SEM images of the particles A and C were unclear, and their diameters could not be confirmed. Accordingly, the calculated curves were fitted not only to the photon energy but also to the relative intensity ratio of each particle. When a is increased, the near-field distribution around the Ag particle broadens and is more strongly affected by air and the substrate, as compared to CdS. Therefore, the effective refractive index around the Ag particle decreases, and the peak of Csca shifts to the high energy side. In addition, the peak intensity of Csca increases because the effect of the optical absorption of CdS decreases. When d is increased, the effective refractive index around Ag and the optical absorption of CdS increase because the volume ratio of CdS increases more that the increase in the near-field distribution around the Ag particle. As a result, the Csca peak shifts to the low-energy side, and the peak intensity decreases. The abovementioned characteristics were used to obtain the unique values of a and d of each particle.
The values of a and d used to calculate Csca in Fig. 3 are shown in Table 1. In the following sections, the sizes of particles A, B, and C are taken as the values indicated in Table 1. The peak photon energy of the linear scattering spectrum of Fig. 3 is denoted as ħωLSP. The ħωLSP of particles A, B, and C were 2.49, 2.40, and 2.29 eV, respectively.
Table 1. Size of the CdS-coated Ag nanoparticles
4.2 Relationship between the complex third-order nonlinear susceptibility and the incident light power density dependency, and their effect on the normalized near-field enhancement factor
The nonlinear optical response of the CdS-coated Ag particle changes with not only the incident light intensity but also the nonlinear complex susceptibility of the material and the excitation situation of the LSP. In a previous study [24], we calculated the particle size dependence of the nonlinear optical response that occurred along with the near-field enhancement on the surface of the particle. However, the relation between the complex nonlinear susceptibility and the nonlinear optical response was not discussed. To clarify this relation for the CdS-coated Ag particle, we performed a computer simulation of the incident light intensity dependency of the near-field enhancement, assuming a variety of complex nonlinear susceptibilities.
The computer simulation of the nonlinear optical response of the CdS-coated Ag particle was performed using a Mie theory considering the optical Kerr effect [23]. The incident light peak power intensity Ii-peak dependency of the normalized near-field enhancement (normalized ηNF) on the surface of CdS (shown by a red dot in Fig. 2) was calculated using various χ(3)CdS values. Figure 4 shows the results of this calculation. To provide an example, a Ag core radius a = 10.0 nm and CdS thickness d = 8.0 nm was assumed.
Fig. 4 Dependence of the normalized near-field enhancement ηNF on the incident light intensity Ii-peak of the CdS-coated Ag nanoparticle in various χ(3)CdS. (simulation) (a)-1, (b)-1, and (c)-1 show the normalized ηNF for various real parts of χ(3)CdS (Im{ χ(3)CdS} = 0). (a)-2, (b)-2, and (c)-2 show the normalized ηNF for various imaginary parts of χ(3)CdS (Re{ χ(3)CdS } = 0). The photon energy of (a), (b), and (c) are ħωi = 0.98 × ħωLSP = 2.35 eV, ħωi = ħωLSP = 2.40 eV, and ħωi = 1.02 × ħωLSP = 2.45 eV, respectively.
Naturally, the Ii-peak dependency of the ηNF changes with the value of χ(3)CdS. In addition, the Ii-peak dependency of the ηNF changes remarkably with the magnitude correlation of ħωi and ħωLSP. For example, in the case of ħωi < ħωLSP, and for the condition that Re{χ(3)CdS} > 0 and Im{χ(3)CdS} = 0, ηNF increases with an increase in Ii-peak, reaches a maximum, and then decreases. On the other hand, for the condition that Re{χ(3)CdS} < 0 and Im{χ(3)CdS} = 0, ηNF only decreases as Ii-peak increases. These behaviors can be interpreted as changes in the LSP excitation condition in the CdS-coated Ag particle, which stem from the permittivity variation of CdS. It is known that the LSP resonance energy shifts to a lower value as the real part of the permittivity around the metallic particle increases.
In case of Re{χ(3)CdS} > 0, as Ii-peak is increased, the real part of εCdS increases and the LSP resonance energy is shifted to a lower value. Therefore, it becomes possible to excite LSP even if it is not excited in the linear response condition for a low Ii-peak. Further, ηNF increases for ħωi < ħωLSP. When Ii-peak is increased further, the LSP resonance energy is shifts to a value with lower LSP resonance energy. Thus, ηNF reaches its maximum value. On the other hand, in case of Re{χ(3)CdS} < 0, as Ii-peak is increased, the real part of εCdS decreases and the LSP resonance energy is shifted to a higher value. The difference between ħωi and the LSP resonance energy grows, and ηNF decreases.
In the case of ħωi = ħωLSP, ηNF decreases as Ii-peak increases, irrespective of the sign, as long as Re{χ(3)CdS} is not 0 (see Fig. 4(b)-1).
Further, in the case of ħωi > ħωLSP, the relationship between the sign of Re{χ(3)CdS} and the Ii-peak dependency of ηNF is opposite to that in the case of ħωi < ħωLSP (see Fig. 4(c)-1). In the case of Re{χ(3)CdS} > 0, as Ii-peak is increased, the real part of εCdS increases and the LSP resonance energy is shifted to a lower value. The difference between ħωi and the LSP resonance energy grows, and ηNF decreases. On the other hand, in case of Re{χ(3)CdS} < 0, as Ii-peak is increased, the real part of εCdS decreases and the LSP resonance energy is shifted to a higher value. It becomes possible to excite LSP even if it is not excited in the linear response condition for a low Ii-peak, and ηNF reaches its maximum value.
In the case of Im{χ(3)CdS} > 0 and Re{χ(3)CdS} = 0, ηNF decreases at any ħωi since the nonlinear optical absorption loss in the CdS increases with the Ii-peak. The remarkable decrease in ηNF is a consequence of the condition that ħωi = ħωLSP. The reason is that, under this condition, the electric field is enhanced according to the LSP excitation, and hence, the nonlinear light absorption loss in CdS is larger for ħωi = ħωLSP than that for ħωi≠ħωLSP, even if the Ii-peak is small.
As mentioned above, the Ii-peak dependency of the ηNF varies with the linear LSP characteristic, the nonlinear susceptibility χ(3)CdS, and the incident photon energy ħωi. In addition, the linear LSP characteristic varies depending on a, d, and neff.
4.3 Third-order nonlinear susceptibility spectra of a CdS-film coated Ag nanoparticle
The nonlinear optical response of ηNF shown in Fig. 4 was caused by the dependence of the LSP resonance spectrum on the light intensity Ii-peak. And, the linear scattering cross section was similar to the shape of the resonance spectrum of the linear near-field light intensity, according to the Mie calculation of the CdS-coated Ag particle used in the experiment. Moreover, the surrounding refractive index dependency of the linear scattering cross section was similar to that of the resonance spectrum of the linear near-field light intensity, according to the Mie calculation of the Ag particle. Therefore, it is hypothesized that the Ii-peak dependency of the scattered light intensity IS-NL of the CdS-coated Ag particle is similar to the Ii-peak dependency of ηNF. In this paper, it was assumed that the Ii-peak dependency of IS-NL/Ii-peak in the CdS-coated Ag particle is proportional to the Ii-peak dependency of the ηNF. The Ii-peak dependencies of the simulation and experimental results for the normalized Is-NL/Ii-peak and ηNF were compared, and the complex χ(3)CdS was chosen such that the curves agreed in both cases. Figure 5 shows the Ii-peak dependencies of the experimental result for the normalized Is-NL/Ii-peak and ηNF. Moreover, Fig. 6 shows the complex third-order nonlinear susceptibility of the χ(3)CdS spectrum obtained from Fig. 5. The χ(3)CdS values obtained this way were almost identical, even though the Ii-peak dependencies of the Is-NL/Ii-peak of particles A, B, and C were different. This result proves that the χ(3)CdS spectrum was correctly measured by our method.
Fig. 5 Dependence of the measured normalized scattered light intensity Is-NL/Ii-peak and the calculated normalized near-field enhancement ηNF on the incident light intensity Ii-peak of the CdS-coated Ag nanoparticle. (a), (b), and (c) show the result for particles A, B, and C, respectively. Dots and curves means normalized Is-NL/Ii-peak and normalized ηNF respectively. The error bars of the normalized Is-NL/Ii-peak indicate the difference between measurements.
Fig. 6 Complex χ(3)CdS spectrum of CdS in the CdS-coated Ag nanoparticle. (a) and (b) are the real and imaginary parts of the χ(3)CdS, respectively. Blue triangles, green dots, and red squares indicate particles A, B, and C, respectively. The error bar indicates the difference from the measurements shown in Fig. 5.
At ħωi > 2.4 eV, it is found that the increase in Re{χ(3)CdS} is of the step type, and at about 2.45 eV, Im{χ(3)CdS} reaches its peak. At ħωi = 2.43 eV, χ(3)CdS is approximately (1.1 + i0.6) × 10−17 m2/V2. In bulk CdS at room temperature, the photoabsorption edge energy Eg-CdS related to the interband transition has been reported to be approximately 2.42 eV [9].
In [26], it was inferred that the nonlinear absorption was a cause since the normalized scattered light intensity decreases with the increase in the incident light intensity. However, since χ(3)CdS is a complex number (according to Fig. 6), it was found that both the nonlinear refractive index and nonlinear absorption of the CdS contributed to the nonlinear optical phenomena exhibited by the CdS-coated Ag particle. Moreover, it was discovered that Re{χ(3)CdS} was more predominant than Im{χ(3)CdS} for ħωi > 2.5 eV. From these features, it is surmised that the carrier generation in interband transitions of the CdS causes an increase in χ(3)CdS for ħωi > 2.4 eV. A previous research reported that for crystalline CdS, χ(3) = 3.5 × 10−9 esu at a wavelength of 514.5 nm [12] and γ = −53 × 10−14 cm2/W at a wavelength of 532 nm [14]. These correspond to χ(3) = 4.8 × 10−17 m2/V2 at ħωi = 2.41 eV and χ(3) = −1.1 × 10−18 m2/V2 at ħωi = 2.33 eV, respectively. On the other hand, our results were χ(3) = (1.1 + i0.6) × 10−17 m2/V2 at ħωi = 2.43 eV and χ(3) < (1.0 + i0.5) × 10−18 m2/V2 at ħωi = 2.34 eV. The order of magnitude and the photon energy dependence of χ(3) are in agreement, although the absolute values of χ(3) were smaller than those obtained in [12] and [14]. We hypothesize that the reason for the small modulus of our χ(3) is that the CdS coating the Ag was an imperfect crystal.
5. Conclusions
In this study, the dependence of the incident light intensity on the scattered light intensity caused by a single CdS-coated Ag nanoparticle was observed, and compared to results of the simulations that used the Mie theory with consideration of the optical Kerr effect. In addition, it reports the formulation of a complex third-order nonlinear susceptibility spectrum near the energy bandgap of the CdS coat film. It was found that the real part of third-order complex nonlinear susceptibility, χ (3), of CdS increased at ħωi > 2.4 eV and that the imaginary part reached its maximum at around 2.45 eV. At ħωi = 2.43 eV, the χ(3) of CdS was (1.1 + i0.6) × 10−17 m2/V2. It is hypothesized that an increase in the carriers in the interband transition of CdS is the reason for the increase in the χ(3) of the CdS at ħωi > 2.4 eV.
This study is the first to experimentally obtain the χ(3) of a material from the variation in the intensity of light scattered by one single nanoparticle. The motivation behind evaluating χ(3) using one nanoparticle is that it facilitates the appearance of nonlinear optical phenomena of the coat medium as part of the light intensity enhancement, because of the LSP excitation, thus facilitating the detection of χ(3). This becomes a useful method to clarify nonlinear optical phenomena of the nanoparticle.
Moreover, this study found that the CdS-coated Ag nanoparticle had high nonlinearity although it was only one particle. Such an optical-Kerr-medium-coated metallic nanoparticle has the potential to become an active device, e.g., an optical modulator of the size of several tens of nanometers.
Acknowledgments
This study was supported by a Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (No. 18310071) and a Grant-in-Aid for Scientific Research on Priority Area from The Ministry of Education, Culture, Sports, Science, and Technology of Japan (No. 20043024 and No. 21020026).
References and links
1. D. Sarid and W. Challener, Modern Introduction to Surface Plasmons (Cambridge, 2010).
2. M. Pelton and G. W. Bryant, Introduction to Metal-Nanoparticle Plasmonics (Wiley, 2013).
3. Y. Inouye and S. Kawata, “Near-field scanning optical microscope with a metallic probe tip,” Opt. Lett. 19(3), 159–161 (1994). [CrossRef] [PubMed]
4. S. Kawata, Y. Inouye, and P. Verma, “Plasmonics for near-field nano-imaging and superlensing,” Nat. Photonics 3(7), 388–394 (2009). [CrossRef]
5. T. Okamoto, I. Yamaguchi, and T. Kobayashi, “Local plasmon sensor with gold colloid monolayers deposited upon glass substrates,” Opt. Lett. 25(6), 372–374 (2000). [CrossRef] [PubMed]
6. G. Raschke, S. Kowarik, T. Franzl, C. Sönnichsen, T. A. Klar, J. Feldmann, A. Nichtl, and K. Kürzinger, “Biomolecular Recognition Based on Single Gold Nanoparticle Light Scattering,” Nano Lett. 3(7), 935–938 (2003). [CrossRef]
7. J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, “Biosensing with plasmonic nanosensors,” Nat. Mater. 7(6), 442–453 (2008). [CrossRef] [PubMed]
8. A. N. Goldstein, C. M. Echer, and A. P. Alivisatos, “Melting in Semiconductor Nanocrystals,” Science 256(5062), 1425–1427 (1992). [CrossRef] [PubMed]
9. K. Rajeshwar, N. R. de Tacconi, and C. R. Chenthamarakshan, “Semiconductor-Based Composite Materials: Preparation, Properties, and Performance,” Chem. Mater. 13(9), 2765–2782 (2001). [CrossRef]
10. P. M. Petersen, “Nonlinear refraction of Gaussian laser beams in CdS at λ =532nm,” J. Lumin. 40–41, 533–534 (1988). [CrossRef]
11. V. N. Semioshko and Y. P. Tsiashchenko, “The Temperature Dependence of The Third-Order Nonlinear Susceptibility in CdS in the Vicinity of the Absorption Edge,” Phys. Status Solidi 184(1), K37–K40 (1994) (b). [CrossRef]
12. Z. Li, G. Xiong, Z. Zhao, and X. Fan, “Measurement of optical nonlinear susceptibility of CdS single crystal using a single beam,” J. Cryst. Growth 138(1-4), 231–233 (1994). [CrossRef]
13. T. D. Krauss and F. W. Wise, “Femtosecond measurement of nonlinear absorption and refraction in CdS, ZnSe, and ZnS,” Appl. Phys. Lett. 65(14), 1739–1741 (1994). [CrossRef]
14. H. P. Li, C. H. Kam, Y. L. Lam, and W. Ji, “Optical nonlinearities and photo-excited carrier lifetime in CdS at 532 nm,” Opt. Commun. 190(1-6), 351–356 (2001). [CrossRef]
15. Y. Nosaka, K. Tanaka, and N. Fujii, “Nonlinear optical susceptibility of ultrasmall CdS particles by means of the polarization-discriminated forward degenerate four-wave mixing in a resonant region,” Appl. Phys. Lett. 62(16), 1863–1865 (1993). [CrossRef]
16. N. Sugimoto, A. Koiwai, S. Hyodo, T. Hioki, and S. Noda, “Nonresonant third-order nonlinear optical susceptibility of CdS clusters encapsulated in zeolite A and X,” Appl. Phys. Lett. 66(8), 923–925 (1995). [CrossRef]
17. Yu. P. Rakovich, M. V. Artemyev, A. G. Rolo, M. I. Vasilevskiy, and M. J. M. Gomes, “Third-Order Optical Nonlinearities in Thin Films of CdS Nanocrystals,” Phys. Status Solidi 224(1), 319–324 (2001) (b). [CrossRef]
18. H. Du, G. Q. Xu, W. S. Chin, L. Huang, and W. Ji, “Synthesis, Characterization, and Nonlinear Optical Properties of Hybridized CdS−Polystyrene Nanocomposites,” Chem. Mater. 14(10), 4473–4479 (2002). [CrossRef]
19. M. Etienne, A. Biney, A. D. Walser, R. Dorsinville, D. L. V. Bauer, and V. Balogh-Nair, “Third-order nonlinear optical properties of a cadmiun sulfide-dendrimer nanocomposite,” Appl. Phys. Lett. 87(18), 181913 (2005). [CrossRef]
20. J. He, W. Ji, G. H. Ma, S. H. Tang, E. S. W. Kong, S. Y. Chow, X. H. Zhang, Z. L. Hua, and J. L. Shi, “Ultrafast and Large Third-Order Nonlinear Optical Properties of CdS Nanocrystals in Polymeric Film,” J. Phys. Chem. B 109(10), 4373–4376 (2005). [CrossRef] [PubMed]
21. Y. Yang, J. Shi, H. Chen, S. Dai, and Y. Liu, “Enhanced off-resonance optical nonlinearities of Au@CdS core-shell nanoparticles embedded in BaTiO3 thin films,” Chem. Phys. Lett. 370(1-2), 1–6 (2003). [CrossRef]
22. W. Jia, F. Guo, E. P. Douglas, and W. Sun, “Two-Photon Absorption and Degenerate Four-Wave Mixing Studies of Sulfide Semiconductor Nanoparticles in Polymeric Solutions,” J. Nanosci. Nanotechnol. 8(3), 1364–1370 (2008). [PubMed]
23. T. Okamoto, M. Haraguchi, and M. Fukui, “Numerical studies of optical switching and optical bistability phenomena of nano- or meso-size spheres,” J. Microsc. 210(3), 193–197 (2003). [CrossRef] [PubMed]
24. T. Okamoto, M. Haraguchi, and M. Fukui, “Light Intensity Enhancement and Optical Nonlinear Response due to Localized Surface Plasmons in Nanosize Ag Sphere,” Jpn. J. Appl. Phys. 43(9A), 6507–6512 (2004). [CrossRef]
25. M. Haraguchi, T. Okamoto, T. Inoue, M. Nakagaki, H. Koizumi, K. Yamaguchi, C. Lai, M. Fukui, M. Kamano, and M. Fujii, “Linear and Nonlinear Optical Phenomena of Metallic Nanoparticles,” IEEE J. Sel. Top. Quantum Electron. 14(6), 1540–1551 (2008). [CrossRef]
26. T. Okamoto, H. Koizumi, M. Haraguchi, M. Fukui, and A. Otomo, “Nonlinear optical response of a CdS-coated Ag particle,” Appl. Phys. Express 1, 062003 (2008). [CrossRef]
27. U. Kreibig and M. Vollmer, Optical Properties of Metal Crusters (Springer, 1995).
28. P. B. Johnson and R. W. Christy, “Optical Constants of the Noble Metals,” Phys. Rev. B 6(12), 4370–4379 (1972). [CrossRef]
29. J. Gottesman and W. F. C. Ferguson, “Optical Properties of Thin Films of Cadmium Sulfide,” J. Opt. Soc. Am. 44(5), 368–370 (1954). [CrossRef]
30. A. Curry, G. Nusz, A. Chilkoti, and A. Wax, “Substrate effect on refractive index dependence of plasmon resonance for individual silver nanoparticles observed using darkfield microspectroscopy,” Opt. Express 13(7), 2668–2677 (2005). [CrossRef] [PubMed]
