Local Charge Carrier Dynamics for Photocatalytic Materials Using Pattern-Illumination Time-Resolved Phase Microscopy

We showed two demonstrations of the local charge carrier dynamics measurements of photocatalytic materials using our recently developed time-resolved phase-contrast microscopic technique combined with the clustering analyses. In this microscopic time-resolved technique, we observed the charge carrier dynamics via the refractive index change instead of the luminescence or absorption change, where we could often observe non-radiative charge carrier processes such as charge carrier trapping and non-radiative relaxation. By the clustering analyses of all the pixel-by-pixel responses, we could extract various different charge carrier dynamics because photocatalytic materials have inhomogeneity on surfaces and the charge carrier behavior depends on the local structure and species. Even for typical photocatalytic materials, titanium oxide and hematite, we could recognize various charge carrier dynamics, which cannot be differentiated by the general fitting procedure for the averaged time response. We could categorize the surface-trapped charge carriers (holes and electrons) and bulk carriers in the nanosecond to millisecond order, which indicates that this analytical procedure will play an important role in understanding the charge carrier dynamics for various photocatalytic materials.