Time-Resolved Fluorescence (or Fluorescence Lifetime) Spectroscopy is an extension of Steady State Fluorescence. Fluorescence lifetimes, occurring as emissive decays from the singlet-state, can also be approximated as those decays occurring in the time region from picoseconds to nanoseconds.
When we discuss time-resolved fluorescence or fluorescence lifetimes, what we are studying is the fluorescence of a sample monitored as a function of time after excitation by a pulse of light.
The time-resolution can be obtained in a number of ways, depending on the required sensitivity and time regions. Edinburgh Instruments employs the technique called Time-Correlated Single Photon Counting (TCSPC), for Time-Resolved Fluorescence, which is used for the acquisition of single photons and allows for time resolutions in the range of picoseconds (ps) to nanoseconds (ns).
In TCSPC the sample is repetitively excited using a pulsed light source with a high repetition rate. During the measurement a probability histogram builds, which relates the time between an excitation pulse (START) and the observation of the first fluorescence photon (STOP).
The fact that the time at which a fluorescence photon is incident on the detector can be defined with picosecond resolution is critical to the operation and precision of TCSPC.
To study lifetime decays slower than this (ns to seconds time range) please see Phosphorescence Lifetime.
To find out more about what TCSPC is and why we use TCSPC, please see the technical notes provided in the resources section.
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