Influence of Crystal Structure, Encapsulation, and Annealing on Photochromism in Nd Oxyhydride Thin Films

[Image: see text] Thin films of rare earth metal oxyhydrides show a photochromic effect, the precise mechanism of which is yet unknown. Here, we made thin films of NdH(3–2x)O(x) and show that we can change the band gap, crystal structure, and photochromic contrast by tuning the composition (O(2–):H(–)) via the sputtering deposition pressure. To protect these films from rapid oxidation, we add a thin ALD coating of Al(2)O(3), which increases the lifetime of the films from 1 day to several months. Encapsulation of the films also influences photochromic bleaching, changing the time dependency from first-order kinetics. As well, the partial annealing which occurs during the ALD process results in a dramatically slower bleaching speed, revealing the importance of defects for the reversibility (bleaching speed) of photochromism.