This presentation contains a basic introduction to quantum dots,their discovery, properties, applications,advantages,limitations and future prospects.It also contains a brief overview of experimental work carried out and results obtained during my summer term project.

1. Created By:
Tanvi Kaple

2. PROJECT TITLE:PROJECT TITLE:
To Study the OpticalTo Study the Optical Properties ofProperties of
CdSCdS Quantum Dots embedded inQuantum Dots embedded in
glass matrix and determine theglass matrix and determine the
energy band gap and size ofenergy band gap and size of
quantum dotsquantum dots

3. VISVESVARAYA NATIONAL INSTITUTE OF TECHNOLOGY,NAGPUR
DEPARTMENT OF PHYSICS
• PROJECT DETAILS
• TEAM MEMBERS:
Sakshi Deshmukh
Sonal Gaikwad
Tanvi Kaple
• PROJECT GUIDE:
Dr. Rupesh .S. Gedam
Department of Physics
VNIT,Nagpur

4. WHAT ARE QUANTUM DOTS?
• Quantum dots (QDs) are semiconductor
nanocrystals with a core–shell structure and a
diameter that typically ranges from 2 to 10 nm.
• They are zero dimensional.
• They display unique electronic properties
intermediate between those of bulk
semiconductors and discrete molecules.
• They have potential applications in electronic
and optoelectronic devices.

5. WHO INVENTED QUANTUM DOTS?
• Quantum dots were discovered in solids (glass crystals) in 1980 by Russian
physicist Alexei Ekimov while working at the Vavilov State Optical Institute.
• In late 1982, American chemist Louis E. Brus, then working at Bell
Laboratories (and now a professor at Columbia University), discovered the
same phenomenon in colloidal solutions.
• He discovered that the wavelength of light emitted or absorbed by a quantum
dot changed over a period of days as the crystal grew, and concluded that the
confinement of electrons was giving the particle quantum properties.
• These two scientists shared the Optical Society of America's 2006 R.W. Wood
Prize for their pioneering work.

6. SYNTHESIS OF QUANTUM DOTS
Few methods of synthesis of quantum dots
are :
• Colloidal Synthesis
• Plasma Synthesis
• Solvothermal Synthesis
• Aqueous and Hydrothermal Synthesis Fig. Cadmium Sulfide
Quantum Dots on Cells

7. OPTICAL PROPERTIES OF QUANTUM DOTS
• The most characteristic property is that their colour is size dependent and
thus can be controlled during synthesis.
• This arises as a result of quantum confinement effect.
• Smaller dots emit higher energy light, that is bluer in colour whereas
larger dots emit lower energy red light.
Fig. As size increases a red shift is observed

8. • QD fluorescence occurs when the excited electron
moves from the conduction band to its valence band,
emitting a photon with a longer wavelength than the
one absorbed (electron–hole recombination process).
• QDs can emit light at wavelengths ranging from the
ultraviolet (UV) to the infrared (IR).
• The properties of QDs include high photostability, high
quantum yield and high molar extinction coefficients
(~10–100-times those of organic dyes).
• They also have narrow symmetrical intense emission at
specific wavelengths, ranging from the UV to the IR.

9. • The bandgap of QDs exhibits a never
observed before direct relationship
to their size.
• The energy band gap is inversely
proportional to the size of quantum
dots.
• We can vary the energy band gap by
changing the size of the quantum
dots.
• This property of quantum dots
makes it possible to use them in a
variety of applications.

10. QUANTUM CONFINEMENT EFFECT
• The quantum confinement effect is observed
when the size of the particle is too small to be
comparable to the wavelength of the electron.
• So as the size of a particle decrease till we a
reach a nano scale the decrease in confining
dimension makes the energy levels discrete and
this increases up the band gap and ultimately
the band gap energy also increases.
• Since the band gap and wavelength are
inversely related to each other the wavelength
decrease with decrease in size and the proof is
the emission of blue radiation . Fig. Density of electronic states v/s Energy

11. APPLICATIONS OF QUANTUM DOTS
Some of the applications of
quantum dots include:
• Solar Cells
• Photocatalysts
• Lasers
• QLED
• Computing
• Biology
QD’S
Antibod
y
Sensor
s
Battery
Cancer
Diagnosis

12. ADVANTAGES AND LIMITATIONS
• A Potential drawback in biological
applications is the fact that due to their
large physical size, they cannot diffuse
across cellular membranes.
• Sometimes, a QD may be toxic for the
cell and inappropriate for any biological
application.
• Quantum Dots may blink and become
invisible.
• Their quite extended lifetime may be a
hindrance to certain applications that
require QDs to biodegrade immediately
after the experiment has been
performed.
• They are highly efficient in
converting short wavelength into
longer wavelength of high purity.
• The quantum dots are quite
stable and can be more easily
handled during manufacturing.
• They are available in various
forms like beads, quantum dust
etc. which makes its range of
applications wider.
• There are multiple methods to
develop them easily and cost
effectively.

13. EXPERIMENTAL WORK
• Objective of the Work:
The aim of this project is to study the effect of size of CdS quantum dots embedded in glass
matrix on their energy band gap and optical properties. An attempt was made to determine
the energy band gap and size of the quantum dots using absorption spectra.
• Synthesis of the sample:
Glass system with 3 wt %CdS was prepared by melt quench technique.
Fig. Glass prepared by melt-quench technique

14. PROCEDURE
• Two different types of heat treatments were given to the glass samples
for the growth of quantum dots:
1. For same temperature and different time duration
2. For same time duration and different temperatures
• The prepared glasses were cut in a suitable shape and polished optically.
• The differential thermal analysis of samples was then carried out and
the glass transition temperature was noted from DTA analysis.
• These glass samples were heat treated with optimized single step heat
treatment schedule at a constant temperature but for three different
time durations.

15. • The glass samples were crushed to powder form to obtain the emission
spectra of the glass samples.
• Another set of glass samples was given heat treatment for constant
time duration and at three different temperatures.
• Optical absorption and PL spectra were then recorded .
• The energy band gap and size of the quantum dots was determined
from the absorption spectra.

16. CALCULATIONS
•

17. CONCLUSIONS
• We can see that with increasing time duration (temperature remaining constant) as well as
in the case of increasing temperature (time remaining constant) the energy band gap is
decreasing and consecutively the size of quantum dots is increasing.
• We can infer that heat treatment has led to the growth of quantum dots in the glass
samples.
• The colour of the glass samples changes to yellow from transparent after heat treatment
which confirms the growth of QDs.
• In the absorption spectra, the cut-off wavelength increases in case of both the types of
heat treatment. This confirms the decrease in energy band gap with increase in size of the
QDs.
• The emission peaks shift towards the longer wavelength side as the time period of heat
treatment is increased.
• Red shift as well as a decrease in the PL intensity with increase in size was observed in the
PL spectra

18. FUTURE PROSPECTS
• Optical computers could use quantum dots in much the same way that
electronic computers use transistors (electronic switching devices)—as the basic
components in memory.
• Dots can be designed so they accumulate in particular parts of the body and
then deliver anti-cancer drugs bound to them. Their big advantage is that they
can be targeted at single organs, such as the liver, much more precisely than
conventional drugs, so reducing the unpleasant side effects that are
characteristic of untargeted, traditional chemotherapy.
• QDs have the potential to be much more than just better fluorophores and
could open up new frontiers beyond conventional testing strategies.