QUANTUM DOTS

• Quantum dots are Semiconductor whose excitons are confined in all three spatial dimensions.
  
• Exciton is a bound state of an electron and an imaginary particle called an electron-hole.
  
• Being zero-dimensional, they have sharp density of states.
  
• Colour of quantum dots dictated by quantum confinement.
  
• Quantum confinement allows tailoring of band-gap of materials.

Quantized energy levels in a quantum dot have no net linear momentum. They do not require any momentum transfer. Transition probabilities are high. This explains the broad-band absorption nature of quantum dots.

Colour of Quantum dots

• Quantum dots of same material with different sizes emit light of different colours.
  
• Larger the dot, redder the fluorescence.
  
• Smaller the dot, bluer the it is.
  
• Larger dots with more closely spaced energy levels absorb photons containing less energy.

Inter band transitions control luminescent properties of quantum dots. Band gap is a function of size of the dots. Hence changing the size of quantum dots can tailor their luminescence. They are produced by colloidal synthesis, electrochemical techniques etc.They have applications as biotags, in diodes, biological sensors, solid-state quantum computation, quantum dot photovoltaic cells.