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What is Phosphorescence? Phosphorescence is a specific

type of photoluminescence related to fluorescence

re-emission of the radiation is not immediate

The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics

A change in electron spin is associated with it.

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One of the first natural phosphorescence observed in1568 by Cellini, while the Bolognan Cobbler, VincenzoCascariolo, synthesized in 1604 the first artificial phosphorby calcining sulphur-rich barium sulphate to give it agolden appearance in daylight

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Historical background

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Theory of Phosphorescence

Light fall and absorption

Radiation less emission

Electron reach a well or valley

Energy stored

Slow re-emission

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Vibrational relaxation

Internal conversion

Pre dissociation

Dissociation

External conversion

Intersystem crossing

Fluorescence

Phosphorescence

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Deactivation Steps

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Process minimizing lifetime of excited state is favored

Vibrational relaxation 10 12- or less

Internal conversion 10-11 sec

Florescence 10-7-10-9sec.

Phosphorescence 10-4-10 or more sec

Some times hours or even days.

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Probability of Deactivation Steps

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Phosphorescence vs. FlorescencePhosphorescence is less probable

Singlet-triplet transition less probable

Average lifetime of triplet state relatively high

Radiation induced excitation to triplet less probable

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Any thing delaying radiation less process and florescence favors phosphorescence

1. Molar absorptivity

2. Structural rigidity

3. Temperature

4. Solvent effect

5. Dissolved oxygen

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Factors influencing Phosphorescence

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Temperature Effect

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Solvent Effect

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Oxygen Effect

Source

Excitation Monochromator

Device for alternately exciting and observing phosphorescence

Sample cell

Emission Monochromator

Detector

Photomultiplier tubes

Recorder

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Instrumentation

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Highly selective method

Determination of organic compounds like petroleum hydrocarbons and pesticides

Biochemical compounds detection: Nucleic acids, Amino acids, Purine, Pyrimidine

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Applications