Dresden 2017 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 34: Focus: Spatio-Temporal Multiscale Optical Spectroscopy Meets Functional Materials (joint session DF/CPP/O, organized by DF)

CPP 34.2: Talk

Wednesday, March 22, 2017, 10:00–10:20, GER 37

Diffuse transient absorption: a tool for investigation of powdery functional materials — •Christoph Merschjann — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, D-14195 Berlin, Germany — Universität Rostock, Institut für Physik, Albert-Einstein-Straße 23-24, D-18059 Rostock, Germany

Transient absorption (TA) spectroscopy is a wide-spread and versatile tool for investigating dynamic processes induced in functional materials. Typical quantities of interest include generation, spatial transport, separation (e.g. at interfaces), and ultimate recombination of (photo)excited charge-carriers, polarons, excitons, etc.
However, most novel functional solids are initially synthesized in powder form, and many applications (e.g. catalysis) demand for rather sponge-like or otherwise rough morphologies. Standard TA spectroscopy, which typically utilizes either direct transmission or specular reflection geometries, does not perform too well for such highly scattering materials.

Here, we present a femtosecond TA spectroscopy setup using diffuse reflection/transmission geometry, showing good results for a variety of functional materials, like polymeric carbon nitrides and TaON. A major challenge is the analysis of the retrieved data. Contrary to standard TA, a simple application of Lambert-Beer’s law is not possible due to a wide distribution of optical pathlengths in the sample. Models and tools for photon propagation and mutual as well as light-matter interaction, to be used alongside those models needed for the kinetics of the excited states themselves, will be discussed.