see also:

fluorescence lifetime imaging microscopy, photoluminescence decay measurements

Fluorescence Lifetime Imaging Microscopy (FLIM) is a microscopy imaging technique where time-correlated single-photon counting (TCSPC) is performed on each pixel of the image. The sample is scanned by a high-frequency pulsed laser beam, single photons of the emitted fluorescence light are detected, and the arrival time of each photon in the laser pulse period is determined by the TCSPC system and recorded in a histogram.

Read more about FLIM in this detailed article.