Fluorescence Spectroscopy

Luminescence – the process of absorption of radiation and re-emmiting it, is called luminescence.Light produced by luminescence is called cold light.

Fluorescence – when beam of light is incident on a surface they emit visible light.this phenomenon is called fluorescence.

Phophorescence – In this phenomenon light is emitted continuously even when the incident light is cut off.

Materials exhibiting fluorescence emit excess radiation within 10-6 to 10-4 se. while materials exhibiting phosphorescence emit light within 10-4 to 20 seconds or longer. Thus lifetime of phosphorescence is longer than fluorescence.


In fluorescence wavelength choices can be made in both emission and absorption wavelengths.
Molecule absorbs light in 10-15 sec.
When the molecule absorbs light it moves to exited state . After this it may return directly to ground state. So there will be no fluorescence.
But in fluorescence the molecule from excited state goes to first singlet excited state and from this it returns to ground state. This is called fluorescence. The movement of electron from the excited state to singlet excited state releases energy by colloisional deactivation. This results in increase of wavelength.
Thus after fluorescence the wavelength of radiation increases.

The time required to execute a vibration is 10-13 sec.