I have observed emission and excitation spectrum intensity reduce by increasing temperature from 08 k to room temperature. What is the major reason ?
Dear Hayat,
I think the increase in temperature causes the particles in the spectrum to become reactive. This causes the particles to move more randomly and the distance between them moves away from each other. The distance and the random motion of these particles blocks the direction of the light so that diffraction occurs and the spectrum intensity is reduced.
Hopefully the answer will shed some light.
The radiative emission process competes with other non-radiative excited state deactivation mechanisms, like rotational relaxation, vibrational deactivation and the like. Increasing the rigidity of a molecule's surrounding makes those pathways more unlikely. Therefore, cooling a almost always increases fluorescence emission intensity. Or, telling it the other way round: increasing temperatures increases non-radiative deactivation, therefore emission intensity goes down on warming up
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