Hidden Photoexcitations\nProbed by Multipulse Photoluminescence

Time-resolved photoluminescence is a validated method\nfor tracking\nthe photoexcited carrier dynamics in luminescent materials. This technique\nprobes the photoluminescence decays upon a periodic excitation by\nshort laser pulses. Herein, we show that this approach cannot directly\ndetect hidden photoexcitations with much slower dynamics than the\nphotoluminescence decay. We demonstrate a new method based on a multipulse\nexcitation scheme that enables an unambiguous detection and an easily\ninterpreted tracking of these hidden species. The multipulse excitation\nconsists of a single pulse (Read) followed by a burst of many closely\nseparated pulses (Write) and finally another single pulse (Read).\nTo illustrate the efficacy of the Read-Write-Read excitation scheme,\nwe apply it to metal halide perovskites to directly visualize carrier\ntrapping, extract the concentration of trapped charges, and determine\nthe rate constant of trap depopulation. The developed approach allows\nstudying performance-limiting processes in energy devices using a\nversatile, highly applicable all-optical method.