元素周期表

Fabrication of Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with enhanced ?uorescence

Huiqin Li a ,b ,Jianmiao Kang a ,Jianhui Yang a ,*,Biao Wu a ,**

a

Key Laboratory of Synthetic and Natural Functional Molecule Chemistry (Ministry of Education),Shaanxi Key Laboratory of Physico-Inorganic Chemistry,College of Chemistry &Materials Science,Northwest University,Xi'an,710069,PR China b

College of Chemistry &Chemical Engineering,Baoji University of Arts &Sciences,Baoji,721013,PR China

a r t i c l e i n f o

Article history:

Received 8January 2016Received in revised form 26February 2016

Accepted 29February 2016Available online 2March 2016Keywords:

Nanofabrications

Mesoporous silica coating Core-spacer-shell structure Luminescence properties

Metal enhanced ?uorescence

a b s t r a c t

Herein,Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites are synthesized through layer-by-layer assembly technology.Au nanoparticle @mSiO 2core e shell nanospheres were prepared at ?rst in the presence of CTAB in aqueous solution system by the modi ?ed one-pot method.A chemical precipitation method and a succeeding calcination process were adopted to the growth of Y 2O 3:Eu shells on the surfaces of Au na-noparticle @mSiO 2core e shell nanospheres.The structure,morphology and composition of the nano-composites were con ?rmed by XRD,TEM and UV e vis absorption spectrum.The prepared Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites have showed the emission intensity enhances to 6.23times at 30nm thickness of the silica spacer between the core of Au nanoparticle and the shell of Y 2O 3:Eu.According to the observations of ?uorescent lifetime and the modeling of local electric ?eld,the metal-enhanced and quenched ?uorescence is closely related with the enhancement of excitation and radiative decay rate and the quenching by NRET comes as a result of competition between the distance-dependent mechanisms.This kind of multifunctional inorganic material will be widely used in elec-tronics,biology and medical drug loading,etc.

?2016Elsevier B.V.All rights reserved.

1.Introduction

Multifunctional inorganic nanoparticles with optical,electrical,magnetic,thermal and other unique characteristics exert the ad-vantages in biological imaging markers,disease diagnosis,laser imaging,optical waveguide,medical chemical detection,etc [1e 6].Some studies pay close attention to noble metal nanoparticles because of its biocompatibility and better chemical stability which are widely used in the biological,chemical sensors,drug carrier,light hyperthermia drug,biological imaging,etc [7e 12].Multi-functional nanoparticles could be obtained by means of physical adsorption,chemical bonding or the layer-by-layer assembly technology.

Fluorescence has become an important means of detection in electronics,biology and medicine [13e 16].Luminescent nano-particles have been developed and used widely as the next gener-ation of ?https://www.360docs.net/doc/827445082.html,nthanide luminescent is widely used in the research of advanced materials due to its narrow spectra,large

Stokes shifts and long lifetimes [17e 19].However,the luminous ef ?ciency of lanthanides is relatively lower leading to its limited application in many ?elds.Metal nanomaterials with surface plasmon resonance are well known to exhibit unique optical properties,which could achieve metal surface ?uorescence enhancement effect in pace with the changes of surface electro-magnetic ?eld subjected to external excitation.A few of studies are pointed at the surface electromagnetic ?eld of metal nanoparticles through the ?nite difference time domain (FDTD)method [20,21].Some of studies have con ?rmed the metal enhanced ?uorescence [22e 25],for example,a range of ?uorophore-doped metal core/silica shell nanocomposites [26e 28].Trivalent-europium (Eu 3t)is used widely for the crystal materials research because the energy level transition of Eu 3tis sensitive when the surrounding magnetic ?eld changes [25,29e 31].Deng et al.[32]reported on the ?uores-cence intensity of BHHCT-Eu-DPBT doped Ag@SiO 2nano-composites varied with the diameter of Ag nanoparticles and the spacer thickness of SiO 2.Zhang et al.[33]studied the metal-enhanced ?uorescence in silica core/silver shell encapsulated with Eu complex.The results revealed that the emission intensity was signi ?cantly enhanced at 20e 30nm of Ag layer thickness with shortened lifetime.In other words,?uorescence enhancement can be achieved through adjusting the interaction between metal

*Corresponding author.**Corresponding author.

E-mail addresses:jianhui@https://www.360docs.net/doc/827445082.html, (J.Yang),wubiao@https://www.360docs.net/doc/827445082.html, (B.

Wu).Contents lists available at ScienceDirect

Journal of Alloys and Compounds

jou rna l homepage:

https://www.360docs.net/doc/827445082.html,/locate/jalcom

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0925-8388/?2016Elsevier B.V.All rights reserved.

Journal of Alloys and Compounds 673(2016)283e 288

nanoparticles and rare earth elements.

Compared with the silver substrate,Au nanoparticles have higher chemical stability,superior surface modi?cation and good biological compatibility,which display many potential advantages for basic research and application of?uorescence.Saboktakin et al.

[34]had investigated the effect of?uorescence intensity enhancement with the different gasket thickness in b-NaYF4doped Yb3t,Er3tand Yb3t,Tm3tby close proximity to metal nano-particles(Au and Ag).As the spacer layer,mesoporous structure of silica with drug loading function has a very good application on the implementation of tumor hyperthermia in medical practice[35,36]. Therefore,we intend to synthesis Au nanoparticle@mSiO2@Y2O3:Eu nanocomposites by the method of layer-by-layer assembly using of spherical Au nanoparticle as the substrate core,the mesoporous silica as the spacer layer and Y2O3:Eu as the outer shell layer.We attempt to seek the relationship between the?uorescence enhancement and quenching with the mesoporous silica spacer thickness.

2.Experimental

The synthetic procedure of Au nanoparticle@mSiO2@Y2O3:Eu nanocomposite is displayed in Fig.1.Au nanoparticle@mSiO2core e-shell nanospheres were prepared in the presence of CTAB in aqueous solution system by the modi?ed one-pot method[37].Au nanoparticle(diameter~10nm)were?rstly obtained by reducing HAuCl4using HCHO as the reducing agent.And then,the deposition of mesoporous silica layer on Au nanoparticle was made by the base-catalyzed hydrolysis of TEOS.Finally,the homogenous pre-cipitation method was used to Y,Eu(OH)CO3$H2O layer coating on Au nanoparticle@mSiO2nanospheres in urea solution at95 C for 40min.After sintered at900 C for1h,the Y,Eu(OH)CO3$H2O layer transforms into cubic phase Y2O3:Eu,realizing the resulting Au na-noparticle@mSiO2@Y2O3:Eu nanocomposites.

2.1.Chemicals

All the chemical reagents used in this experiment were analytical grade without further puri?cation.Cetyl-trimethylammonium bromide(CTAB,99.0wt%),chloroauric acid (HAuCl4,99.999%),formaldehyde solution(37.0wt%),tetraethyl orthosilicate(TEOS,98.0wt%),sodium hydroxide(purity>96%), urea(purity>99%),europium oxide(Eu2O3,>99.99%),and Y(NO3)3?6H2O(purity>99%)were purchased from Beijing Chem-ical Reagents Factory.Deionized water was used for all experi-ments.Eu(NO3)3?6H2O was synthesized using Eu2O3dissolved in concentrated HNO3and the surplus HNO3were removed by evaporation.

2.2.Synthesis Au nanoparticle@mSiO2core e shell nanospheres

Au nanoparticle@mSiO2core e shell nanospheres were synthesized according to the one-step method reported earlier[37].In a typical procedure,CTAB(0.05g),NaOH(0.5M,600m L)and24mL of deionized water were mixed in the Te?on container.The solution was heated to80 C and kept the temperature for15min.After a formaldehyde solution(1mL,37%wt)and HAuCl4(0.04mmol) were added,the solution turned immediately from colorless to gray and eventually to a deep wine-red.After the solution was stirred for 10min,the mesoporous silica coated Au nanoparticles could sub-sequently be obtained by adding a mixed liquid of TEOS and ethanol aging for about6h.The thickness of mesoporous silica spacer could be controlled by adjusting the amount of TEOS.

2.3.Au nanoparticle@mSiO2@Y2O3:Eu nanocomposites

A chemical precipitation method and a succeeding calcination process were adopted to the growth of Y2O3:Eu shells on the sur-faces of Au nanoparticle@mSiO2core e shell nanospheres[29].Brie?y, 1.0mM of Y(NO3)3?6H2O,0.05mM of Eu(NO3)3?6H2O and2.0g of urea were dissolved in100mL deionized water.After heated the solution at95 C for about40min,the precipitate was washed with water and ethanol for three times,and then dried at80 C https://www.360docs.net/doc/827445082.html,stly,Au nanoparticle@mSiO2@Y2O3:Eu3tnanocomposites would be obtained after calcination at900 C for1h.The as-prepared samples were collected and dispersed in the deionized water for further characterization.

2.4.Characterization

The UV e vis absorption spectra were taken with a TU-1901 spectrophotometer.TEM and high-resolution TEM analyses were performed using a JEOL JEM-2010F transmission electron micro-scopy(TEM)equipped with a?eld emission gun operated at 200kV.The X-ray diffraction(XRD)analysis was carried out using a Hitachi S-5500at an accelerating voltage of20kV.The energy-dispersive X-ray spectroscopy(EDS)was obtained through?eld emission scanning electron microscopy(SEM,SIGMA ZEISS).The room temperature?uorescence emission spectra were recorded from570nm to650nm of each system using F-4500?uorescence spectrophotometer of Hitachi Company with the emission slit of 0.5nm intervals and the response time https://www.360docs.net/doc/827445082.html,sol software is used to simulate the calculation of electric?eld around gold nanoparticle.

3.Results and discussion

The phase composition and crystal phase of the nanocomposites were characterized by XRD.Fig.2shows XRD patterns of Au nano-particle@mSiO2and Au nanoparticle@mSiO2@Y2O3:Eu nanocomposites,

respectively.The diffraction peaks in Fig.2a could easily be assigned to the(111),(200),(220),and(311)planes of cubic face-centered Au (JCPDS card PDF#04e0784).The broad peak between20and30 marked as hollow triangle could be originated in the silica(JCPDS card PDF#38e0651)shell on the surface of Au nanoparticle.The Au nanoparticle@mSiO2core e shell structure is further con?rmed by the following TEM investigation.The layer of amorphous Y,Eu(OH) CO3$H2O was then formed on the surface of Au nanoparticle@mSiO

2

Fig.1.Synthetic procedure of the Au nanoparticle@mSiO2@Y2O3:Eu nanocomposite.

H.Li et al./Journal of Alloys and Compounds673(2016)283e288

284

nanosphere by the homogeneous precipitation process.After calcination at 900 C for 1h,the crystalline phase Y 2O 3:Eu was obtained via the decomposition as follows:

Y ;Eu OH eTCO 3$H 2O /Y ;Eu eT2O CO 3eT2tH 2O 2Y ;Eu OH eTCO 3/Y ;Eu eT2O CO 3eT2tH 2O Y ;Eu eT2O CO 3eT2/Y ;Eu eT2O 3t2CO 2

The well-de ?ned diffraction peaks marked as black squares in Fig.2b could be readily indexed to a cubic structure Y 2O 3:Eu (Ia-3space group,JCPDS card PDF#41e 1105).The diffraction data of Y 2O 3doped with Eu is basically anastomotic with puty Y 2O 3sample without other impurity phase.It indicates that Eu could effectively be doped into the Y 2O 3lattice,which may be due to the ionic radius of Eu 3t(88.0pm)is slightly equivalent to Y 3t(88.1pm).The elemental composition of Au,Si,O,Y and Eu in Au nanoparti-cle @mSiO 2@Y 2O 3:Eu nanocomposites was con ?rmed by the EDS analysis as shown in Fig.S1.

In order to achieve the ?uorescence enhancement,the meso-porous silica layer plays a key role of the linker and spacer between Au nanoparticle and lanthanide-doped yttrium oxide.We designed to modify the silica-spacer distance through changing the reaction time and silica precursor concentration.In the synthesis of Au na-noparticle @mSiO 2core e shell nanospheres by the one-pot process,Au nanoparticles with the diameter of about 10nm were ?rstly ob-tained as shown in Fig.3a.The high-resolution TEM image (Fig.3

b)

Fig.2.XRD patterns of (a)Au nanoparticle @mSiO 2and (b)Au nanoparticle @mSiO 2@Y 2O 3:Eu

nanocomposites.

Fig.3.TEM (a)and high-resolution TEM (b)images of Au nanoparticles,TEM images of Au nanoparticle @mSiO 2core e shell nanospheres with different silica thickness of (c)10nm,(d)20nm,(e)30nm,(f)40nm,and (g)50nm,TEM (h)and high-resolution TEM (i)images of Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites,respectively.

H.Li et al./Journal of Alloys and Compounds 673(2016)283e 288285

shows the clear crystalline structure of Au nanoparticles with an interplane distance of 0.24nm corresponding to Au (111)planes.The thickness of the mesoporous silica layer could be well

controlled from about 10to 50nm (Fig.3c e g)by adding different amounts of TEOS.When the Y 2O 3:Eu was deposited on the surface of Au nanoparticle @mSiO 2nanospheres,the core-spacer-shell struc-ture of Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites is formed.The obvious contrast between the layers indicates the existence of the core-spacer-shell structure as shown in Fig.3h.The high-resolution TEM image (Fig.3i)shows the clear lattice fringes dis-tance of 0.3nm,which is corresponding to the (222)lattice con-stant spacing of cubic phase Y 2O 3.

Fig.4a shows the absorption spectra of aqueous dispersions of Au nanoparticles and Au nanoparticle @mSiO 2core e shell nanospheres with different silica thickness.Before coating of silica,Au nano-particles display a characteristic surface plasmon peak at 521nm.As the thickness of silica is increased,the position of the absorption maximum is slightly red shift to 527nm due to the increase in the local refractive index (n silica ?1.4585and n water ?1.3325)around the particles.The maximum of the plasmon band is plotted vs shell thickness as shown in Fig.4b.After deposited Y 2O 3:Eu layer on the surface of Au nanoparticle @mSiO 2core e shell nanospheres,the ab-sorption peak is obviously red shift from 525to 543nm marked with arrow in Fig.4c.This is due to the larger refractive index of yttrium oxide (n ?1.9307).

The ?uorescence performance of Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with different thickness of silica is studied by the ?uorescence emission spectra measured under excitation at 254nm.Fig.5a shows the ?uorescence spectra of Y 2O 3:Eu and Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with different thickness of silica.All the spectra shows three typical emission bands at 591nm,613nm and 629nm with narrow peak width,which come from the transitions of 5D 0/7F J (J ?1,2,and 3)levels of Eu 3tactivators.The spectra also reveals that the ?uorescence of the nanocomposites is enhanced with increasing the silica thick-ness from 10nm to 30nm,and then reduced as the silica thickness beyond 30nm.Fig.5b displays the plots and the ?tting curve of ?uorescence enhancement factors at 613nm verse the silica thickness.It indicates that the ?uorescence intensity of Au nano-particle @mSiO 2@Y 2O 3:Eu nanocomposites strongly depends on the spacer distance between Au nanoparticles and Y 2O 3:Eu shell.The enhancement factor (EF)of excited transitions 5D 0/7F J (J ?1,2,and 3)is calculated at Table 1.The EFs of excited transition 5D 0/7F 1(591nm),5D 0/7F 3(629nm)and 5D 0/7F 2(613nm)reach the maximums of 2.69,2.64,and 6.23at 30nm thickness of silica.There are two possible mechanisms of metal-enhanced ?uo-rescence:one is attributed to the increase of the emission rate by surface plasmon-coupled emission (SPCE),that is an enhancement of radiative decay rate;and the other is an increase of the excitation rate by the local ?eld enhancement (LFE),that is an enhancement of the effective excitation ?ux [38].The quenching of ?uorescence happened due to the non-radiative energy transfer (NRET)by reducing the ef ?ciency from the ?uorescent materials to the metal surface [39].All of these factors strongly depend on the spacing distance between the ?uorescent materials to the metal.The quenching and enhancement of luminescence comes from the competition by the distance-dependent mechanism [40,41].In the current research,Au nanoparticles are used for study the metal-enhanced ?uorescence of Y 2O 3:Eu.The distance of them could be controlled by adjusting thickness of mesoporous silica as spacer layer.It is considered that the SPCE of Au nanoparticle could shorten the ?uorescence lifetime and result in the increase of emission intensity of the ?uorescence.For this purpose,we measured the ?uorescence lifetime of pure Y 2O 3:Eu and Au nano-particle @mSiO 2@Y 2O 3:Eu with different thicknesses of silica spacer layer at 613nm.As shown in Fig.6,it is clear that the ?uorescence lifetime of Au nanoparticle @mSiO 2@Y 2O 3:Eu is shorter than that of pure Y 2O 3:Eu (0.88e 0.95ms VS 1.14ms,Table S1).It is

concluded

Fig.4.UV e vis absorption spectra of (a)Au nanoparticles and Au nanoparticle @mSiO 2core e shell nanospheres with different silica thickness,(b)the linear relationship be-tween the absorption peak and the thickness of the SiO 2spacer,(c)Au nanoparti-cle @mSiO 2and Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with silica thickness of 30nm,respectively.

H.Li et al./Journal of Alloys and Compounds 673(2016)283e 288

286

that the radiation attenuation rate increased is due to the short-ening of the ?uorescence lifetime and the ?uorescence intensity is increased.The quenching of ?uorescence is due to the close prox-imity of the Au nanoparticle with the shell of Y 2O 3:Eu causing NRET from the ?uorescent material to the metallic surface.When the increase of the spacer distance to about 30nm,the SPCE and the LFE became dominant and the EF reached the maximum 6.23.

The electric ?eld around the nanoparticle is enhanced due to the effect of surface plasmon resonance under the condition of external excitation.It leads to an enhancement of the excitation intensity and ef ?ciency of ?uorescent materials.As presented in Fig.7a,a visual electric ?eld change is schematically simulated using the Comsol software.Because of the symmetry of spherical pro ?le,only half of the nanoparticle has to be modeled.The particle is illumi-nated by a plane wave of 500nm.The greatest electric ?eld was found to about 4.0at 525nm.Fig.7b shows the maximum intensity enhancement of the electric ?eld around the nanoparticle as a function of the wavelength of the incident ?eld.The resonance frequency happens at around 520nm,which is consistent with the observation of UV e vis absorption spectra.The enhanced rate of excitation and the emission is proportion to the square of the local electric ?eld.However,the local electric ?eld will be decreased with the increasing of the spacer layer beyond the 30nm distance.The enhancement of excitation and radiative decay rate and the quenching by NRET are sensitive with the distance between the ?uorescent material and the metallic particle.A systematic inves-tigation of metal enhanced ?uorescence need performed by pre-cisely tuning the silica thickness.4.Conclusions

In this paper,Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites are synthesized through layer-by-layer assembly technology.Au nanoparticle @mSiO 2core e shell nanospheres were prepared at ?rst in the presence of CTAB in aqueous solution system by the modi ?ed one-pot method.A chemical precipitation method and a succeed-ing calcination process were adopted to the growth of Y 2O 3:Eu shells on the surfaces of Au nanoparticle @mSiO 2core e

shell

Fig.5.(a)Fluorescence spectra of Y 2O 3:Eu and Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with different thickness of silica.(b)The plots of enhancement factors of red emissions 5D 0/7F 2at 613nm verse silica thickness.(For interpretation of the references to colour in this ?gure legend,the reader is referred to the web version of this article.)

Table 1

The enhancement factor of the Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with different silica thickness.The thickness of silica (nm)

Enhanced factor

Average enhanced factor

5

D 0/7F 15

D 0/7F 2

5

D 0/7F 3

0 1.00 1.00 1.00 1.0010 1.85 2.54 1.17 1.4920 1.85 4.68 1.77 2.7730 2.69 6.23 2.64 3.8540 1.58 3.65 1.74 2.32500.780.930.81

0.84

Fig.6.Decay curves of Y 2O 3:Eu and Au nanoparticle @mSiO 2@Y 2O 3:Eu nanocomposites with different thickness of silica at 613nm.

H.Li et al./Journal of Alloys and Compounds 673(2016)283e 288287

nanospheres.The prepared Au nanoparticle @mSiO 2@Y 2O 3:Eu nano-composites have showed controllable ?uorescence by simply adjusting the thickness of silica layer between the core of Au nanoparticle and the shell of Y 2O 3:Eu.It is found that the emission intensity enhances to 6.23times gradually at ?rst and then relative weakened after the silica thickness is above 30nm.According to the observations of ?uorescent lifetime and the modeling of local electric ?eld,the metal-enhanced and quenched ?uorescence is closely related with the enhancement of excitation and radiative decay rate and the quenching by NRET comes as a result of competition between the distance-dependent mechanisms.Acknowledgments

This work was ?nancially supported by the Scienti ?c Research Foundation of Northwest University (No.13NW121)and the Edu-cation Commission of Shaanxi Province (No.2014JQ6223and 14JS092).

Appendix A.Supplementary data

Supplementary data related to this article can be found at https://www.360docs.net/doc/827445082.html,/10.1016/j.jallcom.2016.02.263References

[1] C.H.Lee,S.H.Cheng,Y.J.Wang,S.H.Cheng,Y.J.Wang,Y.C.Chen,N.T.Chen,

J.Souris,C.T.Chen,C.Y.Mou,C.S.Yang,L.Wei Lo,Adv.Funct.Mater.19(2009)215e 222.

[2]W.Sch €a

rtl,Nanoscale 2(2010)829e 843.[3]G.Li,Y.Zhang,D.Geng,M.Shang,C.Peng,Z.Cheng,J.Lin,ACS Appl.Mater.

Inter.4(2011)296e 305.

[4]T.Mitsudome,Y.Mikami,M.Matoba,T.Mizugaki,K.Jitsukawa,K.Kaneda,

Angew.Chem.Int.Ed.51(2012)136e 139.

[5]S.D.D.Alejandro,E.D.G.Marta,Anal.Chim.Aata 666(2010)1e 22.

[6]J.R.Fu,J.Zheng,W.J.Fang,C.Chen,C.Cheng,R.W.Yan,S.G.Huang,C.C.Wang,

J.Alloys Compd.650(2015)463e 469.

[7] A.Aubry, D.Y.Lei, A.I.Fernandez-Domínguez,Y.Sonnefraud,S.A.Maier,

J.B.Endry,Nano Lett.10(2010)2574e 2579.

[8]T.Ming,L.Zhao,Z.Yang,H.Chen,L.Sun,J.Wang,C.Yan,Nano Lett.9(2009)

3896e 3903.

[9] A.N.Wang,Q.Peng,Y.D.Li,Chem.Mater.23(2011)3217e 3222.

[10]P.K.Jain,X.H.Huang,I.H.El-Sayed,M.A.El-Sayed,Acc.Chem.Res.41(2008)

1578e 1586.

[11] F.Zhang,G.B.Braun,Y.Shi,Y.Zhang,X.Sun,N.O.Reich,D.Zhao,G.Stucky,

J.Am.Chem.Soc.132(2010)2850e 2851.

[12] B.H.Kim,C.H.Cho,J.S.Mun,M.K.Kwon,T.Y.Park,J.S.Kim,C.C.Byeon,J.Lee,

S.J.Park,Adv.Mater.20(2008)3100e 3104.

[13] C.Bradac,T.Gaebel,N.Naidoo,M.J.Sellars,J.Twamley,L.J.Brown,

A.S.Barnard,T.Plakhotnik,A.V.Zvyagin,J.R.Rabeau,Nat.Nano 5(2010)345e 349.

[14] C.Li,J.Lin,J.Mater.Chem.20(2010)6831e 6847.

[15] D.Yang,Y.Dai,P.Ma,X.Kang,Z.Cheng,C.Li,J.Lin,Chem.Eur.J.19(2013)

2685e 2694.

[16]L.Li,R.Zhang,L.Yin,K.Zheng,W.Qin,P.R.Selvin,Angew.Chem.Int.Ed.5

(2012)6121e 6125.

[17]I.Sadiq,I.Khan,E.V.Rebrov,M.N.Ashiq,S.Naseem,M.U.Rana,J.Alloys

Compd.570(2013)7e 13.

[18]G.Liu,B.Jacquier,Spectroscopic Properties of Rare Earths in Optical Mater,

Tsinghua University Press,2005.

[19] D.Parker,R.S.Dickins,H.Puschmann,C.Crossland,J.A.K.Howard,Chem.Rev.

102(2002)1977e 2010.

[20]M.Osman, B.H.Bakr,Wunsch,S.Francesco,Chem.Mater.18(2006)

3297e 3301.

[21]Y.Z.Huang,Y.R.Fang,Z.L.Yang,M.T.Sun,Film.J.Phys.Chem.C 114(2011)

18263e 18269.

[22]N.Gandra,C.Portz,L.M.Tian,R.Tang,B.G.Xu,S.Achilefu,S.Singamaneni,

Angew.Chem.Int.Ed.52(2013)1e 6.

[23]S.Y.Liu,L.Huang,J.F.Li,C.Wang,Q.Li,H.X.Xu,H.L.Guo,Z.M.Meng,Z.Shi,

Z.Y.Li,J.Phys.Chem.C 117(2013)10636e 10642.

[24]H.Naiki,A.Masuhara,S.Masuo,T.Onodera,H.Kasai,H.Oikawa,J.Phys.Chem.

C 117(2013)2455e 2459.

[25]K.K.Haldar,A.Patra,Appl.Phys.Lett.95(2009)063103.

[26]H.Zhang,Y.Li,I.Ivanov,Y.Qu,Y.Huang,X.Duan,Angew.Chem.Int.Ed.49

(2010)2865e 2868.

[27] C.H.Yuan,W.A.Luo,L.N.Zhong,H.J.Deng,J.Liu,Y.T.Xu,L.Z.Dai,Angew.

Chem.Int.Ed.50(2011)3515e 3519.

[28]W.Qin, D.Zhang, D.Zhao,L.Wang,K.Zheng,https://www.360docs.net/doc/827445082.html,m.46(2010)

2304e 2306.

[29]Y.L.Min,Y.Wan,S.H.Yu,Solid State Sci.11(2009)96e 101.

[30] F.Zhang,G.B.Braun,Y.F.Shi,Y.C.Zhang,X.H.Sun,N.O.Reich,D.Y.Zhao,

G.Stucky,J.Am.Chem.Soc.132(2010)2850e 2851.

[31]X.F.Wang,G.H.Peng,N.Li,Z.H.Liang,X.Wang,J.L.Wu,https://www.360docs.net/doc/827445082.html,pd.599

(2014)102e 107.

[32]W.Deng,D.Y.Jin,K.D.Tomsia,J.L.Yuan,J.Wu,E.M.Goldys,Adv.Mater.23

(2011)4649e 4654.

[33]J.Zhang,Y.Fu,R.Joseph,Lakowicz,J.Phys.Chem.C 113(2009)19404e 19410.[34]M.Saboktakin,X.Ye,S.J.Oh,S.H.Hong, A.T.Fafarman,U.K.Chettiar,

N.Engheta,C.B.Murray,C.R.Kagan,ACS.Nano 6(2012)8758e 8766.

[35]Y.F.Sun,Y.L.Sun,L.Z.Wang,J.B.Ma,Y.W.Yang,H.Gao,Microporous.Meso-porous.Mater.185(2014)245e 253.

[36]Z.H.Xu,C.X.Li,X.J.Kang,D.M.Yang,P.P.Yang,Z.Y.Hou,J.Lin,J.Phys.Chem.C

114(2010)16343e 16350.

[37]J.C.Chen,R.Y.Zhang,L.Han,B.Tu,D.Y.Zhao,Nano Res.6(2013)871e 879.[38]R.Joseph,Lakowicz,Anal.Biochem.337(2005)171e 194.

[39]N.Liu,B.S.Prall,V.I.Klimov,J.Am.Chem.Soc.128(2006)15362e 15363.[40]W.Park,D.Lu,S.Ahn,Chem.Soc.Rev.44(2015)2940e 2962.

[41] D.M.Wu,A.Garcia-Etxarri,A.Salleo,J.A.Dionne,J.Phys.Chem.Lett.5(2014)

4020e 4031

.

Fig.7.(a)Local electric ?eld distribution of a 10nm Au nanoparticle from an incoming plane wave of 500nm,the color bar is shown on the side of panel.(b)Plots of the wavelength vs the maximum intensity of electric ?eld as calculated by Comsol for the particle in panel a.(For interpretation of the references to colour in this ?gure legend,the reader is referred to the web version of this article.)

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