Femtosecond diffuse reflectance spectroscopy for studying ultrafast photophysical and photochemical processes of optically scattering materials has been developed and applied to photocatalytic TiO
2 powders. It is demonstrated that the spectroscopy has the similar spectroscopic and temporal resolutions to those of transmittance mode transient absorption one. Temporal behavior of diffuse reflected light is analysed by extended Kubelka-Munk model and simulated numerically. Excitation energy relaxation processes of TiO
2 powders are measured directly in femtosecond to nanosecond time domains, and electron-hole charge separa-tion and recombination dynamics, and charge transfer to adsorbed molecules on TiO
2 surface are made clear. The results are discussed in terms of physical and structural properties of TiO
2 and environmental conditions.
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