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?