Seminar: Photochromic properties of rare-earth metal oxyhydride thin films

Photochromic materials change their absorption properties under light illumination and can be employed in a plethora of applications. While there are numerous materials known to show a photochromic effect (i.e. some transition metal oxides), they typically feature a rather narrow absorption band in the photodarkened state, affecting their appearance, unless doping or multi-layered structures are used. Thin films of several rare-earth metal oxyhydrides (like YHO, GdHO, NdHO, DyHO and ErHO) have been shown to exhibit colour-neutral photochromic properties at ambient conditions. The transmittance of these materials decreases uniformly in the visible and near-infrared region when exposed to light of energy exceeding the band gap of the material. Despite progress made in understanding the behavior of the material, the physics behind the photochromic effect is not yet well understood. In this presentation, I will show how optical properties, including photochromic response, can be manipulated via control of chemical composition, thickness as well as defect structure of the films. The dual-phase nature of this material will be demonstrated and its implication for the mechanism of the photochromic effect will be discussed.