Global luminescence lifetime imaging of thermally activated delayed fluorescence on an auto-phase-locked time-gated microscope

Luminescence lifetime imaging plays an important role in time-resolved detection of luminescence decay differences in microscopic scale. However, the traditional instruments always require expensive detector such as time-correlated single photon counter, stream camera, or intensified CCDs, limiting their practical applications. Herein, a novel approach for global lifetime imaging was developed based on an auto-phase-locked time-gated luminescence microscopy. By utilizing a common color CCD to photograph a set of time-gated luminescence images at different phase differences between the exciting and detecting, a luminescence lifetime image could be obtained by exponential fitting of the gray level of each pixel to the delay time. Compare to the lifetime imaging based on point-by-point scanning, this is a global lifetime measurement of all the pixels, which consumes much less time in detecting long-lifetimes over microseconds. Besides, this method needs no expensive confocal laser scanning systems, intensified CCDs or complex electronic phase matching control, which greatly simplifies the instrument and decreases the cost. This approach was successfully used for fast luminescence lifetime imaging of two classical TADF molecules, which exhibited obvious lifetime differences in microscopic scale. The temporal resolution of the system could reach a few microseconds, suggesting its extensive applicability for many other molecules with long lifetimes.