(QUANTUM DOTS)PRESENTATION BY GAURAV SINGH.pptx
- 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