Temperature‐Dependent Photochromic Performance of Yttrium Oxyhydride Thin Films

Abstract

Yttrium oxyhydride (YHO) is a rare‐earth‐metal oxyhydride that has attracted considerable attention due to its outstanding photochromic properties. The transparency of YHO thin films across the infrared and visible spectral regions is reduced considerably under UV illumination (photodarkening) and recovers when the illumination is removed (bleaching). Although oxygen diffusion has been shown to be necessary for these processes, the exact mechanism for the photochromic behavior is not yet understood. In this work, infrared spectroscopy is utilized to investigate the effect of temperature on the photochromic properties of YHO thin films. The measurements show that YHO can photodarken at temperatures as low as 5 K, where anion diffusion is expected to be severely limited. The bleaching of the films is small, but not zero, for temperatures between 5 and 50 K. A stepwise recovery of the transmittance is observed as the temperature of the films is increased above 100 K up to 250 K. The temperature‐dependent data show that anion diffusion is not required to explain the photochromic behavior of YHO, and that an additional mechanism (or mechanisms), e.g., electronic charge transfer, contributes to the photochromic behavior of YHO, as well as other rare‐earth‐metal oxyhydrides.

Repeatable Photoinduced Insulator-to-Metal Transition in Yttrium Oxyhydride Epitaxial Thin Films

“…However, this scenario is excluded because Baba et al . reported that the absorbance of YO x H y decreases even at 5 K by the illumination of UV light (λ = 405 nm) …”

Photochromic Response of Encapsulated Oxygen‐Containing Yttrium Hydride Thin Films

“…Later, the same group of authors suggested-based on photodarkening results obtained at low temperatures (5 K)-that a simple anion transfer out of the film cannot be responsible for the photochromic process. [22] Herein, we show that encapsulated photochromic REHO films with transparent, nonphotochromic, and thin diffusion barriers perform equally well as uncapped films. Moreover, we prove that the films sealed against the environment are still photochromic and long-time stable as oxidation is inhibited by the diffusion barrier.…”

Large Polaron Conduction, Photoconductivity, and Photochromism in GdOxH3−2x Oxyhydride Thin Films

“…In line with this idea, we note that during illumination, the Gd oxyhydride films reach a conductivity (∽10 −1 Scm −1 ) which is not far from that (∽10 −2 Scm −1 ) of a GdO x H 3 − 2x //GdH x mixedphase sample purposely produced as a reference (Figure S8, Supporting Information). Furthermore, the light-induced volume contraction, and the slow [6,13] temperature activated [20,21] kinetics would follow from the necessary structural rearrangements. The time dependence of the bleaching can be connected to the average rate of disappearance of the metallic domains.…”