Fluorescence-lifetime Imaging Microscopy - Fluorescence Lifetimes

Fluorescence Lifetimes

A fluorophore which is excited by a photon will drop to the ground state with a certain probability based on the decay rates through a number of different (radiative and/or nonradiative) decay pathways. To observe fluorescence, one of these pathways must be by spontaneous emission of a photon. In the ensemble description, the fluorescence emitted will decay with time according to

where

.

In the above, is time, is the fluorescence lifetime, is the initial fluorescence at, and are the rates for each decay pathway, at least one of which must be the fluorescence decay rate . More importantly, the lifetime, is independent of the initial intensity of the emitted light. This can be utilized for making non-intensity based measurements in chemical sensing.