poster New Mexico Consortium 2015
1
A mechanistic study towards biexciton emission enhancement of single QDs near gold nanoparticles Swayandipta Dey, Xiangdong Tian, Julie Jenkins and Jing Zhao , Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT 06269,USA Electric field +++ - - - - - - +++ Electron cloud Metal sphere When metal nanoparticles are excited by electromagnetic radiation, they exhibit collective oscillations of their conduction electrons known as localized surface plasmon resonance (LSPR). The LSPR maximum of the nanoparticles(NPs) are highly sensitive to the size,shape and local dielectric environment which makes them highly functional for applications in photovoltaics,biosensors and even plasmon based waveguides. Localized Surface Plasmon Resonance (LSPR) of Metallic Nanostructures LSPR Substrate Preparation Au Au Au nanoparticles with silica shell silica shell 5 nm silica shell 10 nm Au Au Au Au Au@SiO 2 immobilized on glass Au nanoparticle of 120 nm diameter were synthesized by a two-step seeded growth ap- proach. [1] The 120 nm Au nanoparticles can be coated with silica shells with thickness ranged from 4 to 10 nm based on the method described in ref [2]. The TEM images show the 120 nm Au nanoparticle with a 5 nm and 10 nm silica shell, respectively. Au Au nanoparticles of 120 nm diameter with silica shells were immoblized on APTES silanized glass. The SEM images show the distribution of Au@SiO 2 nanoparticles on glass. The LSPR peak of the Au@- SiO 2 nanoparticles on glass exhibited a red shift with increase in the silica shell thickness due to an effective increase in the local dielectric constant around the Au NPs. LSPR peaks of Au@SiO 2 nanoparticles SEM image of Au@SiO 2 Au@SiO 2 -5nm Au@SiO 2 -10nm Time resolved fluorescence decay of QDs Au QD Au Au Au QD QD Normalized PL Intensity Time (ns) (a) , QDs on Glass (b) , QDs on Au@SiO 2 -5nm (c) , QDs on Au@SiO 2 -10nm a b c g (2) measurements of single QDs on various substrates 100 200 300 400 500 600 0 10 20 30 40 Time (s) Intensity (kcps) 0 2000 0 10 -1 10 0 10 1 10 2 10 -2 10 -1 10 0 10 1 10 2 10 3 Time (s) Number of Event -1 -0.5 0 0.5 1 0 0.2 0.4 0.6 0.8 1 t (Ps) Normalized g (2) on off 100 200 300 400 500 600 0 10 20 30 Time (s) Intensity (kcps) 0 500 Time (s) Number of Event 100 200 300 400 500 600 0 50 100 Time (s) Intensity (kcps) 0 1000 Time (s) Number of Event on off on off Normalized g (2) t (Ps) Normalized g (2) t (Ps) 0 0.2 0.4 0.6 0.8 1 -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 0 0.2 0.4 0.6 0.8 1 10 -1 10 0 10 1 10 2 10 3 10 0 10 1 10 2 10 3 10 -1 10 -1 10 0 10 1 10 2 10 -1 10 0 10 1 10 2 (A) (D) (G) (B) (C) (E) (F) (H) (I) Relative distribution of g (2) minimum data of single QDs 1 0 0.2 0.4 0.6 0.8 1 0 10 20 30 0 4 8 12 16 0 0.2 0.4 0.6 0.8 1 Number of QDs Number of QDs g (2) minimum g (2) minimum glass Au@SiO 2 -5nm 0 0.2 0.4 0.6 0.8 g (2) minimum 0 4 8 12 16 Number of QDs Au@SiO 2 -10nm (A) (B) (C) From the distribution of the g (2) data,it can be observed that majority of the single QDs on Au NP substrates show a higher g (2) value which indi- cates a relatively higher biexciton(BX) quantum yield(QY). Electrodynamics modeling Theoretical explanation of BX emission enhancement : Photon emission statistics and g (2) Ideal single photon source : g ( 2) ( 0 )= 0 This “antibunching” is the signature of a single quantum emitter. filter filter BSP dichroic APD1 APD2 Pulse counters and t 2 -t 1 correlator objective fluorescent emitter Laser Pulse counters: average intensities I 1 ( t ) & I 2 ( t ) Correlator: histogram of photon time separations g (2) ( t ) 2 1 -500 0 500 0 0.2 0.4 0.6 0.8 1 τ = t - t (ns) Schematic of g (2) of a single photon emitter under continuous wave excitation. Complete antibunching is shown here. Ratio of the “dip” to the “plateau” is related to the statistics of the number of photons emitted after excitation, n. [3-4] 1. For a QD with a QY of η 1 the emission intensity of the QD when placed near a metal NP relative to that without a NP can be calculated using = magnitude of electric field enhancement The model can be further extended to any multiexcitonic processes.For biexciton generation the above equation can be modified as Average Silica shell thickness = 5 nm Silica shell thickness = 10 nm |E| 2 1.96 1.90 Rel. X PL Intensity 0.70 0.96 Rel. BX PL Intensity 5.64 4.67 Rel. X PL lifetime 0.20 0.38 Rel. BX PL lifetime 0.68 0.83 X PL QY 0.33 0.48 BX PL QY 0.14 0.13 Ratio (BX QY/ X QY) 0.39 0.26 2. Additional non-radiative processes(k NP,X ) arising due to the energy transfer from the QD to the Au NP has a bigger impact on the X QY than on the BX QY resulting in an increased BX QY but decreased X QY. Theoretical results : The plasmonic effect due to metal NPs results in the changes of X, BX life- times and QYs in single QDs. We hope that these findings will open up new routes to investigate and manipulate the multiexcitonic processes of QDs, and modify their properties for desired applications. References Acknowledgement [1] P. Fang, J. F. Li, Z. L. Yang, L. M. Li, B. Ren, Z. Q. Tian, J. Raman. Spectrosc.2008, 39, 1679. [2] J. F. Li, X. D. Tian, S. B. Li, J. R. Anema, Z. L. Yang, Y. Ding, Y. F. Wu, Y. M. Zeng, Q. Z. Chen, B. Zen, Z. L. Wang, Z. Q. Tian, Nat. Protoc.2013, 8, 52. [3] G. Nair, J. Zhao and M. G. Bawendi, Nano Lett, 2012, 11, 1136. [4] J. Zhao, O. Chen, D. B. Strasfeld and M. G. Bawendi, Nano Lett. 2012, 12, 4477. [1]University of Connecticut Startup Grant and Faculty Large Grant [2]Yadong Zhou,Dr.Shengli Zou,University of Central Florida [3]Dr.Ou Chen,Massachusetts Institute of Technology
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Transcript of poster New Mexico Consortium 2015
A mechanistic study towards biexciton emission enhancement of single QDs near gold nanoparticles Swayandipta Dey, Xiangdong Tian, Julie Jenkins and Jing Zhao , Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs, CT 06269,USA
Electricfield
+++
- - -
- - -
+++
Electroncloud
Metal sphere
When metal nanoparticles are excited by electromagnetic radiation, they exhibit collective oscillations of their conduction electrons known as localized surface plasmon resonance (LSPR). The LSPR maximum of the nanoparticles(NPs) are highly sensitive to the size,shape and local dielectric environment which makes them highly functional for applications in photovoltaics,biosensors and even plasmon based waveguides.
Localized Surface Plasmon Resonance (LSPR) of Metallic Nanostructures
LSPR Substrate Preparation
AuAu
Au nanoparticles with silica shell silica shell 5 nm silica shell 10 nm
Au Au Au Au
Au@SiO2 immobilized on glass
Au nanoparticle of 120 nm diameter were synthesized by a two-step seeded growth ap-proach. [1] The 120 nm Au nanoparticles can be coated with silica shells with thickness ranged from 4 to 10 nm based on the method described in ref [2]. The TEM images show the 120 nm Au nanoparticle with a 5 nm and 10 nm silica shell, respectively.
Au
Au nanoparticles of 120 nm diameter with silica shells were immoblized on APTES silanized glass. The SEM images show the distribution of Au@SiO2 nanoparticles on glass. The LSPR peak of the Au@-SiO2 nanoparticles on glass exhibited a red shift with increase in the silica shell thickness due to an effective increase in the local dielectric constantaround the Au NPs.
LSPR peaks of Au@SiO2
nanoparticles
SEM image of Au@SiO2
Au@SiO2-5nm
Au@SiO2-10nm
Time resolved fluorescence decay of QDs
Au
QD
Au Au Au
QDQD
Nor
mal
ized
PL
Inte
nsit
y
Time (ns)
(a) , QDs on Glass(b) , QDs on Au@SiO2-5nm(c) , QDs on Au@SiO2-10nm
ab c
g(2) measurements of single QDs on various substrates
100 200 300 400 500 6000
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nsity
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s)
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−1 −0.5 0 0.5 10
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) ono�
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0 500Time (s)
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0 1000Time (s)
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ono�
ono�
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t ( s)
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−1 −0.5 0 0.5 1
−1 −0.5 0 0.5 10
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10-1 100 101 102
10-1 100 101 102
(A)
(D)
(G)
(B) (C)
(E) (F)
(H) (I)
Relative distribution of g(2) minimum data of single QDs
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0 0.2 0.4 0.6 0.8 10
10
20
30
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4
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0 0.2 0.4 0.6 0.8 1
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g(2) minimum g(2) minimum
glass Au@SiO2-5nm
0 0.2 0.4 0.6 0.8g(2) minimum
0
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s
Au@SiO2-10nm(A) (B) (C)
From the distribution of the g(2) data,it can be observed that majority of the single QDs on Au NP substrates show a higher g(2) value which indi-cates a relatively higher biexciton(BX) quantum yield(QY).
Electrodynamics modeling
Theoretical explanation of BX emission enhancement :
Photon emission statistics and g(2)
Ideal single photon source : g (2) ( 0 ) = 0
This “antibunching” is the signature of a single quantum emitter.
filter
filter BSP dichroic
APD1
APD2Pulse countersand
t2-t1 correlator
objective
fluorescentemitter
Laser
Pulse counters: average intensities I1 ( t ) & I
2 ( t )
Correlator: histogram of photon time separations g(2) ( t )
2 1
−500 0 5000
0.2
0.4
0.6
0.8
1
τ = t - t (ns)
Schematic of g(2) of a single photon emitter under continuous wave excitation. Complete antibunching is shown here.
Ratio of the “dip” to the “plateau” is related to the statistics of the number of photons emitted after excitation, n. [3-4]
1. For a QD with a QY of η1 the emission intensity of the QD when placed near a metal NP relative to that without a NP can be calculated using
= magnitude of electric field enhancement
The model can be further extended to any multiexcitonic processes.For biexciton generation the above equation can be modified as
Average Silica shell thickness = 5 nm Silica shell thickness = 10 nm |E|2 1.96 1.90
Rel. X PL Intensity 0.70 0.96 Rel. BX PL Intensity 5.64 4.67
Rel. X PL lifetime 0.20 0.38 Rel. BX PL lifetime 0.68 0.83
X PL QY 0.33 0.48 BX PL QY 0.14 0.13
Ratio (BX QY/ X QY) 0.39 0.26
2. Additional non-radiative processes(kNP,X
) arising due to the energy transfer from the QD to the Au NP has a bigger impact on the X QY than on the BX QY resulting in an increased BX QY but decreased X QY.
Theoretical results :
The plasmonic effect due to metal NPs results in the changes of X, BX life-times and QYs in single QDs. We hope that these findings will open up new routes to investigate and manipulate the multiexcitonic processes of QDs, and modify their properties for desired applications.
References
Acknowledgement
[1] P. Fang, J. F. Li, Z. L. Yang, L. M. Li, B. Ren, Z. Q. Tian, J. Raman. Spectrosc.2008, 39, 1679.[2] J. F. Li, X. D. Tian, S. B. Li, J. R. Anema, Z. L. Yang, Y. Ding, Y. F. Wu, Y. M. Zeng, Q. Z. Chen, B. Zen, Z. L. Wang, Z. Q. Tian, Nat. Protoc.2013, 8, 52.[3] G. Nair, J. Zhao and M. G. Bawendi, Nano Lett, 2012, 11, 1136. [4] J. Zhao, O. Chen, D. B. Strasfeld and M. G. Bawendi, Nano Lett. 2012, 12, 4477.
[1]University of Connecticut Startup Grant and Faculty Large Grant[2]Yadong Zhou,Dr.Shengli Zou,University of Central Florida[3]Dr.Ou Chen,Massachusetts Institute of Technology
