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polydimethylsiloxane hybrid materials and their optical limiting property
Journal of Luminescence 190 (2017) 1–5
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Silver nanoparticles/polydimethylsiloxane hybrid materials and their optical limiting property ⁎
Chunfang Lia, Miao Liua, Lei Yana, Na Liua, Dongxiang Lia, , Jing Liub, Xia Wangb,
MARK
⁎
a State Key Laboratory Base of Eco-chemical Engineering, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China b College of Mathematics and Physics, Qingdao University of Science and Technology, Qingdao 266061, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Ag nanoparticles Hybrid materials Optical limiting Nonlinear absorption Nonlinear refraction
To exploit the application potential of Ag nanoparticles (AgNPs) in optical limiting materials, it is significant to develop AgNPs doped polymeric hybrid materials. In this paper, spherical AgNPs were prepared using the seeding growth method. An additional silica coating was employed to obtain the Ag@SiO2 core-shell materials. Then Ag@SiO2 was doped into polydimethylsiloxane(PDMS) rubbers to investigate their optical limiting property to laser at 532 nm. The results showed that the Ag@SiO2 doped PDMS rubber exhibited good optical limiting effect, which should be attributed to the nonlinear optical absorption and refraction. The AgNPs-PDMS hybrid materials would be very promising in optical limiting application area.
1. Introduction
limiting behavior of the nanocomposite in organic solvent was better than that of C60 and the methano-[60]fullerene derivative [7,8]. The better optical limiting performance was attributed to the excited state interaction between the [60]fullerene and silver nanoparticles. Silver nanoparticles prepared by a focused femtosecond laser irradiation in AgNO3 solution in the presence of TiO2 sol exhibited strong self-focused effect and significant optical limiting property [9]. Recently, wellmonodispersed silver nanopentagons were prepared and the nonlinear optical properties were investigated by open aperture Z-scan technique. The silver nanopentagons exhibited intensity-dependent transformation from saturable absorption (SA) to reverse saturable absorption (RSA), and the transformation from SA to RSA was found to be highly dependent on the shape and morphology of the silver nanoparticles [10]. To exploit the application potential of Ag nanoparticles (AgNPs) in optical limiting materials, it is significant to develop AgNPs doped nonlinear polymeric materials due to their relatively low cost, narrow dispersion in the refraction index, virtually endless possibilities of structure modification and good processability [11]. Among the various kinds of polymers, polydimethylsioxane (PDMS) elastomer is of particular interest due to its many useful properties such as distinguished flexibility, low toxicity, chemical inertness, good thermal stability and transparency in the visible region [12,13]. As soft matrix for optical limiting materials, PDMS rubbers can provide excellent chemical and thermal stability in the course of operation. In this article, spherical AgNPs were prepared using the seeding growth method. An additional
Noble metal nanoparticles, especially Au and Ag nanoparticles, have attracted much attention for their excellent properties and application in many important areas [1,2]. Such metal nanoparticles possess strong surface resonance band in the visible to near-infrared regions. The ultrafast nonlinear optical response time facilitates their application in optical communication, all-optical switches and nonlinear optics [3,4]. Therein, optical limiting materials are very important for the manipulation of optical beams in the passive method. Silver nanoparticles with certain size and morphology are significant to exploit optical limiting materials because bulk silver exhibits the highest electrical (or thermal) conductivity among all metals. It was reported that silver-containing nanocrystalline particles in polymer-stabilized suspensions of high linear transmittance had strong limiting effect to lasers at 532 nm. The optical limiting responses of the suspensions were significantly better than those of the benchmark materials fullerene and metallophthalocyanine in solution [5]. Large optical limiting effect from silver-dendrimer nanocomposites in aqueous solution was also reported and the optical limiting performance compared well to the results obtained with other organic structures. The mechanism governing the optical limiting was attributed to nonlinear scattering [6]. A novel [60]fullerene-silver nanocomposite was prepared by in situ reduction of silver ions encapsulated in a monofunctionalized methano-[60]fullerene derivative with reverse micellelike structure. The experimental results demonstrated that the optical
⁎
Corresponding authors. E-mail addresses: [email protected] (D. Li), [email protected] (X. Wang).
http://dx.doi.org/10.1016/j.jlumin.2017.05.023 Received 31 October 2016; Received in revised form 7 April 2017; Accepted 10 May 2017 Available online 11 May 2017 0022-2313/ © 2017 Elsevier B.V. All rights reserved.
Journal of Luminescence 190 (2017) 1–5
C. Li et al.
and transmitted laser pulses under same pulse irradiation were monitored with two FieldMaxII-P laser energy meters (J-10MB-LE energy sensor, Coherent Inc. USA) respectively. For measuring the nonlinear optical properties, Z-scan experiments were conducted on the rubber sample according to the literature [17]. The laser pulse power used in each Z-scan experiment was constant at 21.6 GW/cm2. A focused laser beam was used for irradiating the sample, which was moved along the beam (taken as the z-axis). The scan started from a distance far away from the focus (negative z) to the right (positive z) through the focal point (z=0). For each z position the corresponding transmission was measured. The transmittance through the sample was studied as a function of the sample position z. For comparison, the same experiment was performed for Ag@SiO2 solution housed in quartz cell with a path 1 mm long.
silica coating was employed to obtain the Ag@SiO2 core-shell materials, which could change their solubility, or decrease their propensity to aggregate. Then Ag@SiO2 was doped into PDMS rubbers to investigate their optical limiting property to laser at 532 nm. The results showed that the Ag@SiO2 doped PDMS rubber exhibited good optical limiting effect, and the optical limiting performance was attributed to the nonlinear optical absorption and refraction. 2. Experimental section 2.1. Preparation of AgNPs AgNPs were prepared using the seeding growth method [14]. First, 100 mL solution containing 0.1 mM AgNO3 and 0.3 mM sodium citrate was heated to boiling, then 1 mL of 50 mM NaBH4 was added to the boiling solution under vigorous stirring. The solution was further boiled for 40 min and then left to cool to get the Ag seed solution. Then 20 mL of 50 mM cetyltrimethylammonium bromide (CTAB) solution was mixed with 0.5 mL of 10 mM silver nitrate at 27 °C, to which 1 mL fresh ascorbic acid solution of 100 mM was added to obtain growth solution. Finally, 3 mL of seed solution was added to the growth solution with gentle stirring, followed by dropwise addition of 100 µL of 1 M NaOH. The mixture was further stirred for 6 h. The AgNPs colloids were centrifuged, and resuspended in 2 mM CTAB solution to decrease the content of free CTAB.
3. Results and discussion 3.1. Preparation of AgNPs and Ag@SiO2 Spherical AgNPs were prepared according to the seeding growth method for core-shell particles. Silver seeds were first prepared by the reduction of AgNO3 with NaBH4 under the protection of sodium citrate. Then AgNPs were obtained by reduction of AgNO3 with ascorbic acid in the presence of seed solution in CTAB solution. Fig. 1 shows the UV–vis absorption spectra of Ag seeds and AgNPs solution. For Ag seeds solution, only a surface plasmon band appears at 400 nm, which can be attributed to plasmon resonance of nanosized Ag seeds. The plasmon band red shifts to 435 nm as the Ag seeds grew into AgNPs. Zeta potential was measured for the solution of Ag seeds and AgNPs. The Zeta potential of Ag seeds is −10.6 mV, whereas the Zeta potential of AgNPs is +56.1 mV. So, it is obvious that the surface of Ag seeds is protected by citrate anions, while the AgNPs are covered by CTAB bilayer. The key step during the synthesis of the AgNPs-PDMS nanocomposite hybrids is the mixing of the prepolymer with the nanoparticles colloids in ethanol, so the AgNPs prepared in water should be first transferred into organic phase (ethanol). The surface property of the AgNPs must be properly engineered to avoid the irreversible aggregation of AgNPs in the course of transfer. Silica coating was proved to be an effective method to change the surface character of metal nanoparticles [15,18,19]. Herein, silica coating was adopted to prepare Ag@ SiO2. The silica coating was carried out according to the Stöber-FinkBohn method with MPS as coupling reactant to deposite silica on the surface of the AgNPs. The UV–vis absorption spectrum of Ag@SiO2 is given in Fig. 1. The surface plasmon resonance band appears at 448 nm, and the redshift relative to AgNPs is due to the refractive index increase of the surrounding media. TEM analysis of the AgNPs before and after silica coating was performed. As shown in Fig. 2, the AgNPs have good
2.2. Preparation of Ag@SiO2 colloids Ag@SiO2 colloids were prepared by the literature method [15,16]. 50 µL of 1.08 mM 3-mercaptopropyl trimethoxysilane (MPS) solution in ethanol was added into 10 mL of AgNPs colloids. Ammonium hydroxide was used to adjust the pH of the solution to 9.35. Then 20 µL tetraethyl orthosilicate (TEOS) in 20 µL ethanol was added to the resulting solution and allowed to stand for 12 h. The Ag@SiO2 colloids were transferred into ethanol by repeated centrifugation and ultrasonic dispersion. 2.3. Preparation of AgNPs-PDMS elastomer sheets Ag@SiO2 doped PDMS elastomers were prepared by adding a certain amount of Ag@SiO2 colloids in ethanol into mixture of PDMS prepolymer and curing agent (10:1 weight ratio, SYLGARD 184 from Dow Corning) under stirring. The mixture was poured in a glass container with diameter of 25 mm, vacuum degassed and slow vulcanized at 65 °C for 10–12 h. 2.4. Instruments and optical property measurement UV–vis absorption spectra were obtained using a PERSEE TU-1901 spectrophotometer (Beijing Purkinje General Instrument Co., Ltd). Transmission electron microscopy (TEM) was carried out on a JEOL JEM-2100 electron microscope. Zeta potential measurement was made on a Malvern Nano ZS90 Zetasizer. Thermogravimetric differential thermal measurements (TG-DTA) were performed using a Netzsch STA 449 C thermal analyzer (Selb, Bavaria, Germany) by heating the rubber samples from 286 to 1073 K under air atmosphere at a heating rate of 10 K/min. The optical limiting property of AgNPs /PDMS rubber was measured with Continuum Surelite Laser, which provided 5.0 ns laser pulses at 532 nm with a repetition rate of 10 Hz [3]. The laser pulses are spatially Gaussian, and the beam diameter is approximately 7 mm. The energy of incident laser was adjusted by a polarization analyzer. The beam was split into two beams by the beam splitter, and the reflected beam was used to monitor the incident energy. A lens with a focal length of 100 mm was used to focus the incident beam on the surface of the rubber sheet samples and the beam waist at the focus was 9 µm. The laser was operated in the single shot mode, and the incident
Fig. 1. Normalized UV–vis absorption spectra of Ag seeds, AgNPs and Ag@SiO2 sol.
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Fig. 2. TEM images of AgNPs (a) and Ag@SiO2 (b).
0.002%, 0.003% and 0.005% have linear transmissions of 0.80, 0.67 and 0.39 at 532 nm respectively. Fig. 4 shows the transmitted fluence curves and transmission curves as a function of incident fluences. It can be found that all the samples exhibit strong optical limiting behavior. The transmittances decrease rapidly along with the increase of incident laser fluence. The optical limiting thresholds (input fluence at which the transmittance reduces to 50% of the linear transmittance) are 4.2, 3.3, 3.1 GW/cm2 for 0.002% wt%, 0.003 wt% and 0.005 wt% respectively. The transmittances finally reduced to be 9.0%, 7.7% and 6.6% at 90 GW/cm2. The figure of merit (Transmittance (nonlinear)/Transmittance (linear)) was 0.112, 0.114 and 0.169, and the dynamic range Fluence(at the maximum input fluence)/Fluence(at nonlinear threshold)) was 21.4, 27.3 and 29.0 respectively for the rubber sheets doped with 0.002% wt%, 0.003 wt % and 0.005 wt% AgNPs. Apparently, the sample with more doping amount has the better optical limiting performance, for both the optical limiting threshold and clamped level decrease with the increase of doping concentration. In Fig. 4a, the output irradiance did not get to a marked plateau, which might be ascribed to the relatively low doping
monodispersity and most AgNPs are spherical with a very small percentage of smaller particles. The average diameter of the spherical particles is 25 nm. After silica coating, the AgNPs are coated with thin homogeneous silica shells with average thickness of 18 nm. 3.2. Preparation of AgNPs doped PDMS elastomer sheets and their optical limiting property AgNPs doped PDMS elastomer sheets were prepared by mixing certain amount of Ag@SiO2 in ethanol with PDMS prepolymer. Ethanol was evaporated completely by repeatedly evacuating, and transparent rubber sheets with thickness of 2.5 mm were obtained after vulcanizing. The photos of AgNPs doped PDMS sheets are shown in Fig. 3a. The samples display characteristic yellow due to the surface plasmon absorption band of AgNPs and the increased doping concentration lead to color deepening. UV–vis absorption spectra of AgNPs doped PDMS sheets are given in Fig. 3b. The relatively small spectral change compared with Ag@SiO2 confirmed the good dispersibility of Ag@ SiO2 in the nanocomposites. The samples with doping concentration of
Fig. 3. Photos of AgNPs doped PDMS rubber sheets (a) and the UV–vis absorption spectra of blank rubber sheet and AgNPs doped rubber sheets (b).
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Fig. 4. Optical limiting curves (a) and transmission curves of optical limiting (b) for AgNPs doped PDMS rubber sheets and Ag@SiO2 solution at 532 nm. (The values of the linear transmittance are given in Fig. 4b.).
absorption (SA) and reverse saturable absorption (RSA) happen at the same pump wavelength for different pump intensities [2]. The bleach of the ground-state plasmon band occurring at moderate intensities (SA process) results in an increase of optical transmission, while the significant transient absorption caused by free carriers at increased pump intensities (RSA process) leads to a reduced transmission. But in the course of optical limiting experiment, the increase of optical transmission was not observed, and the humps flanking the valley also did not appear in the open aperture Z-scan curves like literature [8]. For this, the reason is that the samples were not excited at their surface plasmon resonance absorption peaks, so change-over from SA to RSA is not obvious. The closed aperture Z-scan was carried out for the AgNPs doped PDMS rubber sheet sample and the typical closed aperture data are given in Fig. 5b. Since the peak precedes the valley, the signs of the refractive nonlinearity are negative (self-defocusing) [17]. This is a direct consequence of the electron-phonon relaxation in the medium, which is a nonradiative process. Because the PDMS rubber is not good heat conductor, the absorbed heat cannot transfer to surrounding region. The immediate vicinity of the irradiated volume is heated up leading to a reduction in the local refractive index, resulting in the selfdefocusing of the beam. The result is consistent with the literature [22]. The nonlinear refraction can enhance the optical limiting effect to some extent by refracting light away from the energy sensor as opposed to only absorbing of the incident light. Z-scan measurements of the pure PDMS sample were carried out and the results indicated that the blank rubber sample did not absorb the laser irradiation, which was reported
concentrations. Compared with the AgNPs doped PDMS rubber sheets, the Ag@SiO2 solution with linear transmittance of 75.4% exhibits weaker optical limiting effect (Fig. 4). The optical limiting threshold was 8.6 GW/cm2, and the transmittances finally reduced to be 18%. In the experiment, the linear transmittance of the Ag@SiO2 solution was between the PDMS rubber sheets doped with AgNPs (0.002% wt%, 0.003 wt%), and the results indicated that the optical limiting property of the solid rubber materials was enhanced, which is consistent with literature [20]. It is obvious that the optical limiting capability of the AgNPs doped materials is even better than that of gold nanorods doped materials by virtue of the early onset of limiting and large reduction in transmittance [9]. Solid siloxane-based hybrid materials doped with Ptacetylides complexes were also obtained by sol-gel method. Research on optical limiting performance of the Pt-acetylides chromophore in the solid materials showed that the nonlinear optical response in solutions was well preserved [21]. Z-scan experiments are carried out for AgNPs doped PDMS rubber sheet with doping concentration 0.003% and the Ag@SiO2 solution. Open aperture Z-scan transmittance curves are shown in Fig. 5a. It shows that drastic optical extinctions, by the factors of 4.7 and 3.3, occur for the two samples respectively. The smooth valley-shape curves, symmetric about the focal (z=0) position, indicate that both samples exhibit strong nonlinear optical absorption. But the AgNPs doped PDMS rubber sheet displays obvious stronger nonlinear absorption than Ag@ SiO2 solution, which accordingly leads to better optical limiting performance. The Ag nanoclusters belong to a group of materials where saturable
Fig. 5. Open aperture Z-scan transmittance curves (a) and closed aperture Z-scan transmittance curves (b).
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in practical optical limiting applications. Acknowledgments This work was financially supported by the National Natural Science Funds of China (21273123), and the Science and Technology Project (2015GGX102031), Shandong Province, China. References [1] K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, J. Phys. Chem. B 107 (2002) 668–677. [2] T.K. Sau, A.L. Rogach, Adv. Mater. 22 (2010) 1781–1804. [3] G. You, P. Zhou, C. Zhang, Z. Dong, L. Chen, S. Qian, J. Lumin. 119–120 (2006) 370–377. [4] J.-M. Lamarre, F. Billard, C.H. Kerboua, M. Lequime, S. Roorda, L. Martinu, Opt. Commun. 281 (2008) 331–340. [5] Y.-P. Sun, J.E. Riggs, H.W. Rollins, R. Guduru, J. Phys. Chem. B 103 (1999) 77–82. [6] R.G. Ispasoiu, L. Balogh, O.P. Varnavski, D.A. Tomalia, Goodson, J. Am. Chem. Soc. 122 (2000) 11005–11006. [7] N. Sun, Y. Wang, Y. Song, Z. Guo, L. Dai, D. Zhu, Chem. Phys. Lett. 344 (2001) 277–282. [8] Y. Gao, Y. Wang, Y. Song, Y. Li, S. Qu, H. Liu, B. Dong, J. Zu, Opt. Commun. 223 (2003) 103–108. [9] H. Zeng, C. Zhao, J. Qiu, Y. Yang, G. Chen, J. Cryst. Growth 300 (2007) 519–522. [10] C. Zheng, W. Li, W. Chen, X. Ye, Mater. Lett. 116 (2014) 1–4. [11] Y. Chen, Y. Araki, J. Doyle, A. Strevens, O. Ito, W.J. Blau, Chem. Mater. 17 (2005) 1661–1666. [12] M. Chekini, U. Cataldi, P. Maroni, L. Guénée, R. Černý, T. Bürgi, Langmuir 31 (2015) 13221–13229. [13] A. Goyal, A. Kumar, P.K. Patra, S. Mahendra, S. Tabatabaei, P.J.J. Alvarez, G. John, P.M. Ajayan, Macromol. Rapid Commun. 30 (2009) 1116–1122. [14] L. Lu, H. Wang, Y. Zhou, S. Xi, H. Zhang, J. Hu, B. Zhao, Chem. Commun. (2002) 144–145. [15] L.M. Liz-Marzán, M. Giersig, P. Mulvaney, Langmuir 12 (1996) 4329–4335. [16] W. Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci. 26 (1968) 62–69. [17] A.A.S.M. Sheik-Bahae, T.H. Wei, D.J. Hagan, E.W. Van Stryland, IEEE J. Quantum Electron. 26 (1990) 760–769. [18] C. Li, Y. Qi, X. Peng, X. Hao, D. Li, (Part A), J. Lumin. 169 (2016) 191–195. [19] V.I. Boev, J. Pérez-Juste, I. Pastoriza-Santos, C.J.R. Silva, Md.J.M. Gomes, L.M. LizMarzán, Langmuir 20 (2004) 10268–10272. [20] R. Ho-Wu, S.H. Yau, T. Goodson, ACS Nano 10 (2016) 562–572. [21] K. Sridharan, P. Sreekanth, T.J. Park, R. Philip, J. Phys. Chem. C 119 (2015) 16314–16320. [22] R.A. Ganeev, M. Baba, A.I. Ryasnyansky, M. Suzuki, H. Kuroda, Opt. Commun. 240 (2004) 437–448. [23] C. Li, Y. Qi, X. Hao, X. Peng, D. Li, Appl. Phys. A 121 (2015) 11–15.
Fig. 6. Thermogravimetry patterns of PDMS rubber sheets.
in literature [23]. The thermal properties of the rubber samples were investigated by TG-DTA analysis as shown in Fig. 6. There are two distinct steps of mass losses: the first weight loss between 315 °C and 373 °C was ascribed to the loss of organic groups linked with Si atoms and the second weight loss between 468 °C and 608 °C could be attributed to the breakage of Si-O bonds. For the sample doped with AgNPs, the residue was more than the blank sample and the PDMS rubbers provided good thermal stability in the course of operation. 4. Conclusion Spherical AgNPs were prepared according to the seeding growth method, and then silica coating was carried out on the surface of AgNPs to prepare Ag@SiO2. AgNPs-PDMS hybrid sheets were prepared by doping Ag@SiO2 into PDMS prepolymer. The AgNPs-PDMS hybrid sheets exhibit better optical limiting property than Ag@SiO2 solution and gold nanoclusters by virtue of the early onset of limiting and large reduction in transmittance. Z-scan experiments results showed the optical limiting performance was attributed to the nonlinear absorption and refraction. The AgNPs-PDMS hybrid materials would be promising
5
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Silver nanoparticles/polydimethylsiloxane hybrid materials and their optical limiting property ⁎
Chunfang Lia, Miao Liua, Lei Yana, Na Liua, Dongxiang Lia, , Jing Liub, Xia Wangb,
MARK
⁎
a State Key Laboratory Base of Eco-chemical Engineering, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China b College of Mathematics and Physics, Qingdao University of Science and Technology, Qingdao 266061, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Ag nanoparticles Hybrid materials Optical limiting Nonlinear absorption Nonlinear refraction
To exploit the application potential of Ag nanoparticles (AgNPs) in optical limiting materials, it is significant to develop AgNPs doped polymeric hybrid materials. In this paper, spherical AgNPs were prepared using the seeding growth method. An additional silica coating was employed to obtain the Ag@SiO2 core-shell materials. Then Ag@SiO2 was doped into polydimethylsiloxane(PDMS) rubbers to investigate their optical limiting property to laser at 532 nm. The results showed that the Ag@SiO2 doped PDMS rubber exhibited good optical limiting effect, which should be attributed to the nonlinear optical absorption and refraction. The AgNPs-PDMS hybrid materials would be very promising in optical limiting application area.
1. Introduction
limiting behavior of the nanocomposite in organic solvent was better than that of C60 and the methano-[60]fullerene derivative [7,8]. The better optical limiting performance was attributed to the excited state interaction between the [60]fullerene and silver nanoparticles. Silver nanoparticles prepared by a focused femtosecond laser irradiation in AgNO3 solution in the presence of TiO2 sol exhibited strong self-focused effect and significant optical limiting property [9]. Recently, wellmonodispersed silver nanopentagons were prepared and the nonlinear optical properties were investigated by open aperture Z-scan technique. The silver nanopentagons exhibited intensity-dependent transformation from saturable absorption (SA) to reverse saturable absorption (RSA), and the transformation from SA to RSA was found to be highly dependent on the shape and morphology of the silver nanoparticles [10]. To exploit the application potential of Ag nanoparticles (AgNPs) in optical limiting materials, it is significant to develop AgNPs doped nonlinear polymeric materials due to their relatively low cost, narrow dispersion in the refraction index, virtually endless possibilities of structure modification and good processability [11]. Among the various kinds of polymers, polydimethylsioxane (PDMS) elastomer is of particular interest due to its many useful properties such as distinguished flexibility, low toxicity, chemical inertness, good thermal stability and transparency in the visible region [12,13]. As soft matrix for optical limiting materials, PDMS rubbers can provide excellent chemical and thermal stability in the course of operation. In this article, spherical AgNPs were prepared using the seeding growth method. An additional
Noble metal nanoparticles, especially Au and Ag nanoparticles, have attracted much attention for their excellent properties and application in many important areas [1,2]. Such metal nanoparticles possess strong surface resonance band in the visible to near-infrared regions. The ultrafast nonlinear optical response time facilitates their application in optical communication, all-optical switches and nonlinear optics [3,4]. Therein, optical limiting materials are very important for the manipulation of optical beams in the passive method. Silver nanoparticles with certain size and morphology are significant to exploit optical limiting materials because bulk silver exhibits the highest electrical (or thermal) conductivity among all metals. It was reported that silver-containing nanocrystalline particles in polymer-stabilized suspensions of high linear transmittance had strong limiting effect to lasers at 532 nm. The optical limiting responses of the suspensions were significantly better than those of the benchmark materials fullerene and metallophthalocyanine in solution [5]. Large optical limiting effect from silver-dendrimer nanocomposites in aqueous solution was also reported and the optical limiting performance compared well to the results obtained with other organic structures. The mechanism governing the optical limiting was attributed to nonlinear scattering [6]. A novel [60]fullerene-silver nanocomposite was prepared by in situ reduction of silver ions encapsulated in a monofunctionalized methano-[60]fullerene derivative with reverse micellelike structure. The experimental results demonstrated that the optical
⁎
Corresponding authors. E-mail addresses: [email protected] (D. Li), [email protected] (X. Wang).
http://dx.doi.org/10.1016/j.jlumin.2017.05.023 Received 31 October 2016; Received in revised form 7 April 2017; Accepted 10 May 2017 Available online 11 May 2017 0022-2313/ © 2017 Elsevier B.V. All rights reserved.
Journal of Luminescence 190 (2017) 1–5
C. Li et al.
and transmitted laser pulses under same pulse irradiation were monitored with two FieldMaxII-P laser energy meters (J-10MB-LE energy sensor, Coherent Inc. USA) respectively. For measuring the nonlinear optical properties, Z-scan experiments were conducted on the rubber sample according to the literature [17]. The laser pulse power used in each Z-scan experiment was constant at 21.6 GW/cm2. A focused laser beam was used for irradiating the sample, which was moved along the beam (taken as the z-axis). The scan started from a distance far away from the focus (negative z) to the right (positive z) through the focal point (z=0). For each z position the corresponding transmission was measured. The transmittance through the sample was studied as a function of the sample position z. For comparison, the same experiment was performed for Ag@SiO2 solution housed in quartz cell with a path 1 mm long.
silica coating was employed to obtain the Ag@SiO2 core-shell materials, which could change their solubility, or decrease their propensity to aggregate. Then Ag@SiO2 was doped into PDMS rubbers to investigate their optical limiting property to laser at 532 nm. The results showed that the Ag@SiO2 doped PDMS rubber exhibited good optical limiting effect, and the optical limiting performance was attributed to the nonlinear optical absorption and refraction. 2. Experimental section 2.1. Preparation of AgNPs AgNPs were prepared using the seeding growth method [14]. First, 100 mL solution containing 0.1 mM AgNO3 and 0.3 mM sodium citrate was heated to boiling, then 1 mL of 50 mM NaBH4 was added to the boiling solution under vigorous stirring. The solution was further boiled for 40 min and then left to cool to get the Ag seed solution. Then 20 mL of 50 mM cetyltrimethylammonium bromide (CTAB) solution was mixed with 0.5 mL of 10 mM silver nitrate at 27 °C, to which 1 mL fresh ascorbic acid solution of 100 mM was added to obtain growth solution. Finally, 3 mL of seed solution was added to the growth solution with gentle stirring, followed by dropwise addition of 100 µL of 1 M NaOH. The mixture was further stirred for 6 h. The AgNPs colloids were centrifuged, and resuspended in 2 mM CTAB solution to decrease the content of free CTAB.
3. Results and discussion 3.1. Preparation of AgNPs and Ag@SiO2 Spherical AgNPs were prepared according to the seeding growth method for core-shell particles. Silver seeds were first prepared by the reduction of AgNO3 with NaBH4 under the protection of sodium citrate. Then AgNPs were obtained by reduction of AgNO3 with ascorbic acid in the presence of seed solution in CTAB solution. Fig. 1 shows the UV–vis absorption spectra of Ag seeds and AgNPs solution. For Ag seeds solution, only a surface plasmon band appears at 400 nm, which can be attributed to plasmon resonance of nanosized Ag seeds. The plasmon band red shifts to 435 nm as the Ag seeds grew into AgNPs. Zeta potential was measured for the solution of Ag seeds and AgNPs. The Zeta potential of Ag seeds is −10.6 mV, whereas the Zeta potential of AgNPs is +56.1 mV. So, it is obvious that the surface of Ag seeds is protected by citrate anions, while the AgNPs are covered by CTAB bilayer. The key step during the synthesis of the AgNPs-PDMS nanocomposite hybrids is the mixing of the prepolymer with the nanoparticles colloids in ethanol, so the AgNPs prepared in water should be first transferred into organic phase (ethanol). The surface property of the AgNPs must be properly engineered to avoid the irreversible aggregation of AgNPs in the course of transfer. Silica coating was proved to be an effective method to change the surface character of metal nanoparticles [15,18,19]. Herein, silica coating was adopted to prepare Ag@ SiO2. The silica coating was carried out according to the Stöber-FinkBohn method with MPS as coupling reactant to deposite silica on the surface of the AgNPs. The UV–vis absorption spectrum of Ag@SiO2 is given in Fig. 1. The surface plasmon resonance band appears at 448 nm, and the redshift relative to AgNPs is due to the refractive index increase of the surrounding media. TEM analysis of the AgNPs before and after silica coating was performed. As shown in Fig. 2, the AgNPs have good
2.2. Preparation of Ag@SiO2 colloids Ag@SiO2 colloids were prepared by the literature method [15,16]. 50 µL of 1.08 mM 3-mercaptopropyl trimethoxysilane (MPS) solution in ethanol was added into 10 mL of AgNPs colloids. Ammonium hydroxide was used to adjust the pH of the solution to 9.35. Then 20 µL tetraethyl orthosilicate (TEOS) in 20 µL ethanol was added to the resulting solution and allowed to stand for 12 h. The Ag@SiO2 colloids were transferred into ethanol by repeated centrifugation and ultrasonic dispersion. 2.3. Preparation of AgNPs-PDMS elastomer sheets Ag@SiO2 doped PDMS elastomers were prepared by adding a certain amount of Ag@SiO2 colloids in ethanol into mixture of PDMS prepolymer and curing agent (10:1 weight ratio, SYLGARD 184 from Dow Corning) under stirring. The mixture was poured in a glass container with diameter of 25 mm, vacuum degassed and slow vulcanized at 65 °C for 10–12 h. 2.4. Instruments and optical property measurement UV–vis absorption spectra were obtained using a PERSEE TU-1901 spectrophotometer (Beijing Purkinje General Instrument Co., Ltd). Transmission electron microscopy (TEM) was carried out on a JEOL JEM-2100 electron microscope. Zeta potential measurement was made on a Malvern Nano ZS90 Zetasizer. Thermogravimetric differential thermal measurements (TG-DTA) were performed using a Netzsch STA 449 C thermal analyzer (Selb, Bavaria, Germany) by heating the rubber samples from 286 to 1073 K under air atmosphere at a heating rate of 10 K/min. The optical limiting property of AgNPs /PDMS rubber was measured with Continuum Surelite Laser, which provided 5.0 ns laser pulses at 532 nm with a repetition rate of 10 Hz [3]. The laser pulses are spatially Gaussian, and the beam diameter is approximately 7 mm. The energy of incident laser was adjusted by a polarization analyzer. The beam was split into two beams by the beam splitter, and the reflected beam was used to monitor the incident energy. A lens with a focal length of 100 mm was used to focus the incident beam on the surface of the rubber sheet samples and the beam waist at the focus was 9 µm. The laser was operated in the single shot mode, and the incident
Fig. 1. Normalized UV–vis absorption spectra of Ag seeds, AgNPs and Ag@SiO2 sol.
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Fig. 2. TEM images of AgNPs (a) and Ag@SiO2 (b).
0.002%, 0.003% and 0.005% have linear transmissions of 0.80, 0.67 and 0.39 at 532 nm respectively. Fig. 4 shows the transmitted fluence curves and transmission curves as a function of incident fluences. It can be found that all the samples exhibit strong optical limiting behavior. The transmittances decrease rapidly along with the increase of incident laser fluence. The optical limiting thresholds (input fluence at which the transmittance reduces to 50% of the linear transmittance) are 4.2, 3.3, 3.1 GW/cm2 for 0.002% wt%, 0.003 wt% and 0.005 wt% respectively. The transmittances finally reduced to be 9.0%, 7.7% and 6.6% at 90 GW/cm2. The figure of merit (Transmittance (nonlinear)/Transmittance (linear)) was 0.112, 0.114 and 0.169, and the dynamic range Fluence(at the maximum input fluence)/Fluence(at nonlinear threshold)) was 21.4, 27.3 and 29.0 respectively for the rubber sheets doped with 0.002% wt%, 0.003 wt % and 0.005 wt% AgNPs. Apparently, the sample with more doping amount has the better optical limiting performance, for both the optical limiting threshold and clamped level decrease with the increase of doping concentration. In Fig. 4a, the output irradiance did not get to a marked plateau, which might be ascribed to the relatively low doping
monodispersity and most AgNPs are spherical with a very small percentage of smaller particles. The average diameter of the spherical particles is 25 nm. After silica coating, the AgNPs are coated with thin homogeneous silica shells with average thickness of 18 nm. 3.2. Preparation of AgNPs doped PDMS elastomer sheets and their optical limiting property AgNPs doped PDMS elastomer sheets were prepared by mixing certain amount of Ag@SiO2 in ethanol with PDMS prepolymer. Ethanol was evaporated completely by repeatedly evacuating, and transparent rubber sheets with thickness of 2.5 mm were obtained after vulcanizing. The photos of AgNPs doped PDMS sheets are shown in Fig. 3a. The samples display characteristic yellow due to the surface plasmon absorption band of AgNPs and the increased doping concentration lead to color deepening. UV–vis absorption spectra of AgNPs doped PDMS sheets are given in Fig. 3b. The relatively small spectral change compared with Ag@SiO2 confirmed the good dispersibility of Ag@ SiO2 in the nanocomposites. The samples with doping concentration of
Fig. 3. Photos of AgNPs doped PDMS rubber sheets (a) and the UV–vis absorption spectra of blank rubber sheet and AgNPs doped rubber sheets (b).
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Fig. 4. Optical limiting curves (a) and transmission curves of optical limiting (b) for AgNPs doped PDMS rubber sheets and Ag@SiO2 solution at 532 nm. (The values of the linear transmittance are given in Fig. 4b.).
absorption (SA) and reverse saturable absorption (RSA) happen at the same pump wavelength for different pump intensities [2]. The bleach of the ground-state plasmon band occurring at moderate intensities (SA process) results in an increase of optical transmission, while the significant transient absorption caused by free carriers at increased pump intensities (RSA process) leads to a reduced transmission. But in the course of optical limiting experiment, the increase of optical transmission was not observed, and the humps flanking the valley also did not appear in the open aperture Z-scan curves like literature [8]. For this, the reason is that the samples were not excited at their surface plasmon resonance absorption peaks, so change-over from SA to RSA is not obvious. The closed aperture Z-scan was carried out for the AgNPs doped PDMS rubber sheet sample and the typical closed aperture data are given in Fig. 5b. Since the peak precedes the valley, the signs of the refractive nonlinearity are negative (self-defocusing) [17]. This is a direct consequence of the electron-phonon relaxation in the medium, which is a nonradiative process. Because the PDMS rubber is not good heat conductor, the absorbed heat cannot transfer to surrounding region. The immediate vicinity of the irradiated volume is heated up leading to a reduction in the local refractive index, resulting in the selfdefocusing of the beam. The result is consistent with the literature [22]. The nonlinear refraction can enhance the optical limiting effect to some extent by refracting light away from the energy sensor as opposed to only absorbing of the incident light. Z-scan measurements of the pure PDMS sample were carried out and the results indicated that the blank rubber sample did not absorb the laser irradiation, which was reported
concentrations. Compared with the AgNPs doped PDMS rubber sheets, the Ag@SiO2 solution with linear transmittance of 75.4% exhibits weaker optical limiting effect (Fig. 4). The optical limiting threshold was 8.6 GW/cm2, and the transmittances finally reduced to be 18%. In the experiment, the linear transmittance of the Ag@SiO2 solution was between the PDMS rubber sheets doped with AgNPs (0.002% wt%, 0.003 wt%), and the results indicated that the optical limiting property of the solid rubber materials was enhanced, which is consistent with literature [20]. It is obvious that the optical limiting capability of the AgNPs doped materials is even better than that of gold nanorods doped materials by virtue of the early onset of limiting and large reduction in transmittance [9]. Solid siloxane-based hybrid materials doped with Ptacetylides complexes were also obtained by sol-gel method. Research on optical limiting performance of the Pt-acetylides chromophore in the solid materials showed that the nonlinear optical response in solutions was well preserved [21]. Z-scan experiments are carried out for AgNPs doped PDMS rubber sheet with doping concentration 0.003% and the Ag@SiO2 solution. Open aperture Z-scan transmittance curves are shown in Fig. 5a. It shows that drastic optical extinctions, by the factors of 4.7 and 3.3, occur for the two samples respectively. The smooth valley-shape curves, symmetric about the focal (z=0) position, indicate that both samples exhibit strong nonlinear optical absorption. But the AgNPs doped PDMS rubber sheet displays obvious stronger nonlinear absorption than Ag@ SiO2 solution, which accordingly leads to better optical limiting performance. The Ag nanoclusters belong to a group of materials where saturable
Fig. 5. Open aperture Z-scan transmittance curves (a) and closed aperture Z-scan transmittance curves (b).
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in practical optical limiting applications. Acknowledgments This work was financially supported by the National Natural Science Funds of China (21273123), and the Science and Technology Project (2015GGX102031), Shandong Province, China. References [1] K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, J. Phys. Chem. B 107 (2002) 668–677. [2] T.K. Sau, A.L. Rogach, Adv. Mater. 22 (2010) 1781–1804. [3] G. You, P. Zhou, C. Zhang, Z. Dong, L. Chen, S. Qian, J. Lumin. 119–120 (2006) 370–377. [4] J.-M. Lamarre, F. Billard, C.H. Kerboua, M. Lequime, S. Roorda, L. Martinu, Opt. Commun. 281 (2008) 331–340. [5] Y.-P. Sun, J.E. Riggs, H.W. Rollins, R. Guduru, J. Phys. Chem. B 103 (1999) 77–82. [6] R.G. Ispasoiu, L. Balogh, O.P. Varnavski, D.A. Tomalia, Goodson, J. Am. Chem. Soc. 122 (2000) 11005–11006. [7] N. Sun, Y. Wang, Y. Song, Z. Guo, L. Dai, D. Zhu, Chem. Phys. Lett. 344 (2001) 277–282. [8] Y. Gao, Y. Wang, Y. Song, Y. Li, S. Qu, H. Liu, B. Dong, J. Zu, Opt. Commun. 223 (2003) 103–108. [9] H. Zeng, C. Zhao, J. Qiu, Y. Yang, G. Chen, J. Cryst. Growth 300 (2007) 519–522. [10] C. Zheng, W. Li, W. Chen, X. Ye, Mater. Lett. 116 (2014) 1–4. [11] Y. Chen, Y. Araki, J. Doyle, A. Strevens, O. Ito, W.J. Blau, Chem. Mater. 17 (2005) 1661–1666. [12] M. Chekini, U. Cataldi, P. Maroni, L. Guénée, R. Černý, T. Bürgi, Langmuir 31 (2015) 13221–13229. [13] A. Goyal, A. Kumar, P.K. Patra, S. Mahendra, S. Tabatabaei, P.J.J. Alvarez, G. John, P.M. Ajayan, Macromol. Rapid Commun. 30 (2009) 1116–1122. [14] L. Lu, H. Wang, Y. Zhou, S. Xi, H. Zhang, J. Hu, B. Zhao, Chem. Commun. (2002) 144–145. [15] L.M. Liz-Marzán, M. Giersig, P. Mulvaney, Langmuir 12 (1996) 4329–4335. [16] W. Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci. 26 (1968) 62–69. [17] A.A.S.M. Sheik-Bahae, T.H. Wei, D.J. Hagan, E.W. Van Stryland, IEEE J. Quantum Electron. 26 (1990) 760–769. [18] C. Li, Y. Qi, X. Peng, X. Hao, D. Li, (Part A), J. Lumin. 169 (2016) 191–195. [19] V.I. Boev, J. Pérez-Juste, I. Pastoriza-Santos, C.J.R. Silva, Md.J.M. Gomes, L.M. LizMarzán, Langmuir 20 (2004) 10268–10272. [20] R. Ho-Wu, S.H. Yau, T. Goodson, ACS Nano 10 (2016) 562–572. [21] K. Sridharan, P. Sreekanth, T.J. Park, R. Philip, J. Phys. Chem. C 119 (2015) 16314–16320. [22] R.A. Ganeev, M. Baba, A.I. Ryasnyansky, M. Suzuki, H. Kuroda, Opt. Commun. 240 (2004) 437–448. [23] C. Li, Y. Qi, X. Hao, X. Peng, D. Li, Appl. Phys. A 121 (2015) 11–15.
Fig. 6. Thermogravimetry patterns of PDMS rubber sheets.
in literature [23]. The thermal properties of the rubber samples were investigated by TG-DTA analysis as shown in Fig. 6. There are two distinct steps of mass losses: the first weight loss between 315 °C and 373 °C was ascribed to the loss of organic groups linked with Si atoms and the second weight loss between 468 °C and 608 °C could be attributed to the breakage of Si-O bonds. For the sample doped with AgNPs, the residue was more than the blank sample and the PDMS rubbers provided good thermal stability in the course of operation. 4. Conclusion Spherical AgNPs were prepared according to the seeding growth method, and then silica coating was carried out on the surface of AgNPs to prepare Ag@SiO2. AgNPs-PDMS hybrid sheets were prepared by doping Ag@SiO2 into PDMS prepolymer. The AgNPs-PDMS hybrid sheets exhibit better optical limiting property than Ag@SiO2 solution and gold nanoclusters by virtue of the early onset of limiting and large reduction in transmittance. Z-scan experiments results showed the optical limiting performance was attributed to the nonlinear absorption and refraction. The AgNPs-PDMS hybrid materials would be promising
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