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seminar class
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Joined: Feb 2011
02-03-2011, 04:09 PM


.pptx   phosphorescence.pptx (Size: 97.08 KB / Downloads: 69)
Luminescence: It is the process of emitting a part of absorbed energy in the form of EMR of longer wavelength.
Simply luminescence is regarded as “light without heat” or “cold light”
* Fluorescence
* Phosphorescence
If there are ‘n’ number of unpaired electrons it means that (n+1) fold equal energy states will be associated with the electron spin, regardless of the molecular orbital occupied. Thus if no unpaired electrons are present(n=0),there is only 1 spin state. Such a state is called “singlet state.”
SINGLET EXCITED STATE:Most of the molecules in their ground state do not have unpaired electrons(singlet state). When such a molecule absorbs uv or visible radiation of proper frequency one or more of that paired electrons get raised to an excited singlet state.
Here in this state the spin of the electron does not undergo any change and the net spin is zero.
1. Nature of molecules
2. Nature of substituent's
a)Electron donating groups like –NH2
b)High atomic number atom introduction
3. Effect of concentration
4. Light
5. Oxygen
6. Temperature and viscosity
The instrument used for the measurement of phosphorescence is known as phosphorimeter.
Compounds with phosphorescence are likely to fluoresce as well.Hence, a phosphorimeter must be capable of distinguish between the two.
It has been achieved by a “rotating shutter” which may also be known as “phosphoroscope.”
The spectrophosphorimeter is similar to spectrofluorimeter except the former is fitted with:
1)a rotting shutter device
Determination of aspirin(acetyl salicylic acid) in blood serum with high sensitivity by phosphorimetry at liquid nitrogen temperatures. 0.02-1mg aspirin per ml of serum can be analyzed.
Low concentrations of procaine, cocaine, Phenobarbital and chlorpromazine in blood serum have been determined.

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