Mg-Ni-H films as selective coatings: tunable reflectance by layered   hydrogenation
  Unlike other switchable mirrors, Mg2NiHx films show large changes in reflection that yield very low reflectance (high absorptance) at different hydrogen contents, far before reaching the semiconducting state. The resulting reflectance patterns are of interference origin, due to a self-organized layered hydrogenation mechanism that starts at the substrate interface, and can therefore be tuned by varying the film thickness. This tunability, together with the high absorptance contrast observed between the solar and the thermal energies, strongly suggests the use of these films in smart coatings for solar applications. 
J.L.M. van Mechelen, B. Noheda, W. Lohstroh, R.J. Westerwaal, J.H.   Rector, B. Dam and R. Griessen