It describes the essential information regarding quantum dots, a nanomaterials.

1. QUANTUM DOTS
Department of Chemistry
School of Chemical Sciences and Pharmacy
CENTRAL UNIVERSITY OF RAJASTHAN
Bandar Sindri, Ajmer- 305801
Submitted to:
Dr. Jony Saha
Assistant Professor
Central University of Rajasthan
Presentation by:
Soham Thakur
Integrated M.Sc. B.Ed. Chemistry
2018IMSBCH014 1

2. Quantum Dot ?
What is it ?
I am Quantum Dot, a tiny man-
made semiconductor
nanoparticle.
My family members have size in
between 2-10nm.
2
 Zero dimensional relative to the bulk.
 Limited number of electrons results in
discrete energy levels for
non-aggregated zero dimensional
structures.
 Treated as a box in quantum
mechanical system.
 Emit various colours upon being hit
by UV light.
Alivisatos, A.P., J. Phys. Chem., 1996, 100, 13226–13239
Bera, D.; Qian, L.; Holloway, P.H., John WIley & Sons, Ltd: West Sussex, UK, 2008.

3. Quantum
Dot
Quantum
Discrete energy states
Dot
Zero Dimensional
Contd.
Bera, D., et. al., Materials, 2010, 3(4), 2260–2345.
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4. Antiquity Records
 Alexi Ekimov, Russian physicist discovered Quantum dots for the first time in late 1970s.
 In 1982, Russian physicist, Alexander Efros, proposed the first theory to explain the
behaviour of quantum dots.
 American Chemist, Louis, first colloidal Quantum Dots of cadmium sulphide,
easier to handle, and published his results in 1983.
https://nexdot.fr/en/history-of-quantum-dots/ 4

5. Characteristics
Quantum Confinement
Effect and Band Gap
 Widening of band gap with a decrease in size of QDs
 When electron and hole approaches each other they
form an exciton.
 Exciton Bohr radius for bulk materials can be given by:
me, mh are effective masses of electrons and holes,
ε, ћ, and e are the optical dielectric constant,
reduced Planck’s constant and the charge of an
electron.
 As, QD radius R rB or R<rB, motion of carriers is confined
spatially to the dimension of QD.
V/S
 Exciton Binding
energy
 Quantum
confinement
effect
 Exciton Binding
energy
 Quantum
confinement
effect
>
>
Klimov, V.I., J. Phys. Chem. B, 2006, 110, 16827–16845.
Bera, D., et. al., Materials, 2010, 3(4), 2260–2345
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≈

6. Luminescence
Properties
Contd.
 Electronic transition occur from ground state to excited
energy state, upon external excitation.
 So, electrons and holes possess high energy.
 Excess energy due to recombination and relaxation give
rise to luminescence.
 Intermittent luminescence which is called ‘blinking’.
Fig: Blinking effect during luminescence from a
single 2.9 nm sized CdSe QD
Kuno, M., et. al., J. Chem. Phys., 2000, 112, 3117–3120.
Bera, D., et. al., Materials, 2010, 3(4), 2260–2345
6

7. Synthesis
Top Down Approach
Bulk
T
H
I
N
E
D
QD
Electron beam lithography, Reactive ion etching, Wet chemical etching are
used to achieve QDs.
Fig: Schematic Representation of the approach
Focused Ion Beam Technique offers high precision in fabricating QDs.
Electron Beam Lithography offers high degree of flexibility in the design.
Incorporation of impurities into the QDs and structural imperfections by
Patterning are the drawbacks.
Wang, J. et. al., Current Pharmaceutical Design, 2015, 21, 000-000
Chason, E., et. al., J. Appl. Phys., 1997, 81, 6513–6561.
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8. Contd.
Bottom Up Approach
Precursor
molecules
QD
C
O
N
D
E
S
E
D
Fig: Schematic Representation of the approach
Wet Chemical Methods and Vapour phase Methods are category of self
assembly techniques to synthesize QDs.
Sol gel process, emulsion process, hot solution process are few popular
techniques under wet chemical category.
Simplicity, cost effectiveness, suitability for scale up, ease in control of size
are attributed as positive points.
Low yield and incorporation of impurities to some extent pulls it back.
Wang, J. et. al., Current Pharmaceutical Design, 2015, 21, 000-000
Bera, D., et. al., Materials, 2010, 3(4), 2260–2345 8

9. Characterization
Instrumentations Information gathered
UV-VIS and Photoluminescence
Spectroscopy
Optical Characterisation
Photo modulated Reflectance Spectroscopy For checking deposited QD structures
SEM, TEM, AFM, DLS studies Morphology of QDs
Field Flow fractionation Characterisation of water soluble QDs
Scanning Tunneling Spectroscopy To study quantum size effects
XPS, NMR QD surface chemistry study
Ultracentrifugation Surface Chemistry and size distribution
Drbohlavova J., et. al., Int. J. Mol. Sc., 2009,10(2): 656–673. 9

10. Contd.
Fig: SEM image of oil soluble
CdSe/ZnS Quantum dots
Fig: XPS spectra of a graphene
quantum dots
Fig: AFM images of CdSe/ZnS
quantum dots embedded in protein
Zhang H., Analytical Letters, 2017, 51(6):921-934 Sarkar S., Phys. Chem. Chem. Phys., 2016, 18(31)
Kumar P., Nanoscale Research Letters, 2014, 9(1):179
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11. Applications
QDs
Electroluminescence
Device Fabrication
Detection of latent
fingerprints
Phenol waste water
treatment
Applications in
optoelectronic devices
Bio-imaging applications
Detection of explosive
TNT
Downconversion of Blue
or Ultraviolet Light
Solar Cell Device
Fabrication
Bera, D., et. al., Materials, 2010, 3(4), 2260–2345 Liang. H., et. al., Optical Materials, 2020, 100, 109674
Dilag J., et. al., Forensic Science International, 2009, 187(1-3), 97-102 11

12. Conclusion
So, zero dimensional nanostructure has many advances in the field of
fundamental as well as applied science
QD exhibit significantly different optical, physical and electronic properties as
compared to bulk materials
Bottom up approach has been widely explored to generate methods to
synthesize QDs.
Nanobiotechnology, kinetics of synthesis of QD are the topics to explore
further.
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