Understanding Fluorescence Lifetime: Calculation and Significance

Fluorescence, laser physics phenomenon, refers to light emission by a substance after excitation with a light pulse. The incident energy increases molecular energy, which excite the molecules into higher-unstable energy levels. The excited molecules later decay to lower-stable energy levels by emitting longer-wavelength light. Fluorescence lifetime, decay constant, is the amount of time that a molecule stays in the excited state. Because fluorescence lifetime depends on structural rigidity and environmental parameters of substance, theoretical lifetime can provide diagnostic information in medicine and radiation physics. Lifetime is an indicator of the time available to gather information from the emission profile.

Instructions

• 1

  Compute intensity ratio (Io/I). Divide original fluorescence intensity (Io) to fluorescence intensity measured after a specified time (I) with the aid of a calculator to obtain a dimensionless value.

• 2

  Evaluate the "logarithm to base e of intensity ratio." Evaluate a value for "Ln(Io/I)" with the aid of a calculator to obtain a single dimensionless value.

• 3

  Determine the reciprocal of "logarithm to base e of intensity ratio." Divide one (1) by the value for "Ln(Io/I)" with the aid of a calculator to obtain a single dimensionless value.

• 4

  Calculate theoretical fluorescence lifetime. Multiply measured time (t) in seconds by the reciprocal of "logarithm to base e of intensity ratio" with the aid of a calculator to obtain a theoretical fluorescence lifetime in seconds.