Quantum dots are nanoscale semiconductor crystals that exhibit quantum confinement effects, influencing their optical and electrical properties. They can be tuned by size and have a range of applications, including light emitters, biological imaging, and solar cells. Their unique properties make them useful in various fields, such as quantum computation and medicine.

1. QUANTUM DOTS
BY : GAURAV SINGH
DEPARTMENT OF PHYSICS
HNBGU, A CENTRAL UNIVERSITY

2. INTRODUCTION:
 QUANTUM DOTS are nanometerscale semiconductor crystals composed of
group II-VI (e.g.CdS ,CdSe ) or III-V elements.
 They are defined as particles with physical dimensions smaller than the
exciton bohr radius which are confined in all 3 dimensions of space.
 They obey the basic principle of quantum confinement .
 The term quantum dot was coined by MARK REED in 1988 ; however they
were first discovered in a glass matrix by ALEXEY EKIMOV in 1981 and in
colloidal solutions by LOUIS E. BRUS in 1985.

3. Quantum Confinement:
 The spatial confinement of excitons in one or more dimension within a
material basically observed at dimensions below 10nm .
 Quantum dots are bandgap tunable by size. We can engineer their optical
and electrical properties
 Smaller QDs have a large bandgap.
 Absorbance and luminescence spectrums are blue shifted with decreasing
particle size.
Energy
650 nm
555 nm

4. PROPERTIES OF QUANTUM DOTS:
 Nanocrystals (2-10 nm) of semiconductor compounds.
 Can be of different shapes (cube , sphere , pyramid etc.)
 Small size leads to confinement of excitons.
 Quantized energy levels and altered relaxation dynamics.
 Examples: CdSe, PbSe, PbTe, InP.

5. APPLICATIONS OF QUANTUM DOTS :
 Light emitters
 Biological applications
 Quantum computation
 Solar cells

6. LIGHT EMITTERS:
 The discovery of quantum dots has led to the development of an entirely new
range of materials for the active regions in LEDs and laser diodes.
 Indirect gap semiconductors that don’t luminesce in their bulk form such as Si
become efficient light emitters at the nanoscale due quantum confinement
effects.

7. Absorption and emission Spectra of CdSe/ZnS QDs compared to
Rhodamine
 The absorption spectrum (dashed lines) of the QD (green) is very broad, whereas
that of the organic die (orange) is narrow.
 Conversely, the emission spectrum (solid lines) of the QD is more narrow than that
of the organic die
• Jyoti K. Jaiswal and Sanford M. Simon. Potentials and pitfalls of fluorescent quantum
dots for biological imaging. TRENDS in Cell Biology Vol.14 No.9 September 2004

8. BIOLOGICAL
APPLICATIONS:
• Biological assays and
microarrays
• Biological Tagging
and Labeling
• Labeling of cells and
intracellular
structures
• Pathogen and Toxin
detection • CdSe/ZnS QDs used to image cancer cells in a live mouse.
Gao, Xiaohu. "In vivo cancer targeting and imaging with." Nature Biotechnology 22(2004): 8

9. REFERENCE :
 http://nanohub.org
 www.researchgate.net/post/what_is_Quantum_confinement_effect