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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper II covers physical chemistry.

UPSC Combined Geo-Scientist, Mains · 2017 · Mains Paper II

Q13(b). Fluorescence and phosphorescence lifetimes

Question

Why is the average phosphorescence lifetime longer than the fluorescence lifetime? Explain using a Jablonski diagram.

Answer in brief

Fluorescence is usually spin-allowed S₁→ S₀ emission; phosphorescence is spin-forbidden T₁→ S₀ emission and normally has a smaller radiative rate.

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CoversFluorescencephosphorescence lifetimesPhotophysics

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