Quantum dots are nanocrystalline semiconductor particles between 1-10 nm in size that display quantized energy levels. Their spectral properties depend on their size - smaller quantum dots emit higher energy light while larger ones emit lower energy. This allows using quantum dots of different sizes to produce a range of colors. Potential applications of quantum dots include use in TV and display technologies due to their pure colors and long lifetimes. Quantum dots are also being explored for biological and chemical applications such as cancer treatment where they can target organs more precisely than conventional drugs.
3. QUANTUM DOTS
Quantum dots are small particles of a semiconductor, a
nanocrystalline material
Typical dimensions range from 1-10 nm
In an atom, the energy levels are quantized due to the
confinement of electrons
QDs are produce distinctive colors determined by the
size of particles
4. Quantum dots have unique spectral properties :
Broad absorption
Narrow emission
Wavelength depends on size
7. How atoms make light. After
absorbing energy:
a. An electron inside an atom is
promoted to a higher energy
level further from the nucleus
b. When it returns, the energy is
given out as a photon of light
c. The color of the light
depends on the energy levels
and varies from one atom to
another.
Quantum dots produce light in a similar way because
the electrons and holes constrained inside then give
then similarly discrete, quantized energy levels.
However, the energy levels are governed by the size
of the dot rather than the substance from which it’s
made
9. In quantum dots, the energy levels become discrete and
the energy gap becomes larger, compared to a bulk
made of the same material
Band gap is very critical parameter in many electronic
and optical application
According to Quantum mechanics, energy of photons
relates to the wavelength (color) of photons, this means
When light behaves like conductor, some electrons are
jump from valence band to conduction band
Returning electrons from conduction band to valence band
release photons with amount of energy equal to band gap
10. Various size of QDs results in quantum confinement
and hence, different band gap.
Different band gap of QDs results in different color emit
QDs are artificially prepared nanostructured, which have
many varied properties depend on their size
Increasing Size
Varied Colors
Different size
2nm 3nm 4nm 5nm 7nm
Color controlled by QDs particle size
13. TYPES OF QUANTUM DOTS
Quantum dots are made largely from the elements:
o II and VI group of the period system - Cadmium
chalcogenides (CdS, CdSe, CdTe), zinc (ZnS, ZnSe,
ZnTe), and
o III and V groups - Phosphides and Indium
arsenides
15. APPLICATIONS
1. Quantum Dots TVs and Display
Due to their unique physical properties of QDs, they
will be at the core of next-generation displays
Compared to organic luminescent material used in
organic light emitting diodes [OLEDs], QD based
materials have purer colors, longer lifetime, lower
manufacturing cost and lower power consumption.
16. 2. Biological and Chemical applications
QDs are findings important medical applications,
including potential cancer treatment.
Advantage: Targeted at single organs, such as liver
much more precisely than conventional drugs.
QDs are being used in place of organic dyes in
biological research.
Eg.: They can be used like nanoscopic light bulbs to
light up and color specific tells that needs to be
studied under a microscope.
17. ADVANTAGES
OF QUANTUM
DOTS
QDs can substitute bulk,
expensive, and inefficient
materials
QDs adsorb photons of light
and then re-emit longer
wavelength photons for a
period of time
The high control over the
wavelength of the reemitted
photon
QDs require only a small
amount of energy to be
excited
QDs can be used in various
forms. Eg.: as small crystal in
liquid solutions, as quantum
dust and in bead form. All
these existing forms make