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Fluorescence Spectroscopy Principles

Fluorescence Spectroscopy Principles :

- Interaction of photons with molecules results in promotion of valence electrons from ground state orbitals to high energy levels.
- The molecules are said to be in excited state.
- Molecules in excited state do not remain there long but spontaneously relax to more stable ground state.
- The relaxation process is brought about by collisional energy transfer to solvent or other molecules in the solution.
- Some excited molecules however return to the ground state by emitting the excess energy as light.

- This process is called fluorescence.

The emitted light has two important characteristics :
1. It is usually of longer wavelength (lower energy) than the excited light.  This is because part of the energy associated with S state is lost as heat energy.
2. The emitted light is composed of many wavelengths which results in fluorescence spectrum.