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Synthesis and Characterization of Quantum Dots in a Perfluorinated Ionomer
DJENABOU DIAWARA, JONATHAN DOAN AND SMOTKIN’S BAND
OverviewIntroduction to Quantum Dots
Host Matrix Membrane (Nafion)
Synthesis of CdS and PbS Quantum Dots in NafionDetecting QDs Formation with IR
Characterization of CdS and PbS UV/Vis SpectraExciton Energy
Fluorescence SpectraBand Gap Energy
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What is Quantum Dots ?Quantum Dots are semiconductor nanoparticles.
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J. Shen, Y. Zhu, X. Yang, C. Li. Chemical Communications 2012, 48, 3686-3699. R. Liu, H. Huang, H. Li, Y. Liu, J. Zhong, Y. Li, S. Zhang, Z. Kang. ACS Catal. 2013.
"Lg Tv - Google Search." Lg Tv - Google Search. Web. 11 Aug. 2015.
PhotovoltaicsFlat Panel Displays Biomedical Imaging
Drummen, G. (2010, January 13). Retrieved August 11, 2015, from http://www.mdpi.com/1422-0067/11/1/154
Exciton Energy and Band Gap Energy Characterized Semiconductors (QDs)
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An Exciton energy is the energy required to form an exciton.
During exciton relaxation, light is emitted. The energy of light emitted is equal to the band gap energy.
Exciton
Conduction band
Valence band
Band Gap
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Band Gap Energy is Inversely Proportional to the Particle’s Size and to the Wavelength
Quantum confinement
Coulomb attraction
Radius of the particle
Band gap energy
Equation 1: Brus equation for energy of emitted light in QDs
h: Planck’s constant.me*: mass of electron at rest.
ε
Equation 2: Energy of wavelength conversion
wavelength of light
ε-
mh*: mass of electron hole pair at rest.Ɛo : permittivity of a vacuum.
Ɛr : relative permittivity.C: speed of light.
http://www.cyberphysics.co.uk/topics/radioact/Radio/EMSpectrumcolor.jpg
Light emitted depends on the size of the Particles
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http://informationdisplay.org/IDArchive/2013/JanuaryFebruary/FrontlineTechnologyQuantumDotDisplays.aspx http://www.cyberphysics.co.uk/topics/radioact/Radio/EMSpectrumcolor.jpg
Structure of Cadmium Sulfide and Lead Sulfide
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Cadmium Sulfide (CdS) Lead Sulfide (PbS)
Band gap energy 2.4ev
Engineering devices
Band gap energy of 0.41ev
Easy to manipulate its sizehttp://geology.com/minerals/galena.shtmlhttp://en.wikipedia.org/wiki/Quantum_dot#/media/File:Colloidal_nanoparticle_of_lead_sulfide_(selenide)_with_complete_passivation.png
Nafion is the Ideal Host Matrix Membrane
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Repeat Unit
Hydrophilic (Ion Exchange Site)
Hydrophobic
Flexible Teflon Backbone
Ion Exchange Capability
Large Ion Channels
Quantum dots Particles are Formed in Nafion by an Ion-exchange Technique
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Hydrated Cd2+/ Pb2+ exchanged Nafion
Dehydrated Cd2+ /Pb2+ exchanged Nafion
SO3-
Cd2+/Pb2+
H2O
H+
Cadmium Sulfide (CdS)/ Lead Sulfide (PbS) are Formed in Nafion
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Cd2+ + 2SO3- + H2S CdS + 2HSO3
Pb2+ + 2SO3- + H2S PbS + 2HSO3
Cadmium Sulfide Lead Sulfide
SO3
Nafion
H
CdS/PbS
Difference Between IR Spectra
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1405
969
969 cm-1
1405 cm-1
Nafion + Cd2+
Nafion + CdS
Nafion1059
910
Difference Between IR Spectra
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1405
Nafion + Pd2+
Nafion + PdSNafion
1059
969
910
1405
UV/vis and Exciton Energy of CdS and PbS Particles
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The energy required to form an exciton in PbS particle is 2.06 ev
The energy required to form an exciton in CdS particle is 4.13 ev
ε
PbS
CdS
300 nm
600 nm
Fluorescence and Band Gap Energy of Cadmium Sulfide (CdS) and Lead Sulfide (PbS) Particles
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PbS
CdS
659 nm400 nm
Band gap energy of PbS is 1.88 ev
Band gap energy of CdS is 3.1ev
ε
PbSCdS
Band Gap Energy Decreases Particle’s Size and Wavelength increase
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Band Gap Energy Particle size Wavelength
0.9 nm
1.52 nm
400 nm
659 nm
3.1 ev
1.88 ev
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Cadmium SulfideLead Sulfide
Ion exchange Dehydration
QDs Formed
H2S Reaction
Acknowledgements
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Dr. Oyindasola Oyelaran
Dr. Patricia Ann Mabrouk
Dr. Carla Mattos
Dr. Eugene Smotkin
Jonathan Doan
Neili Loupe
Smotkin Lab
Thank you! Questions?