Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen-Containing Yttrium Hydride Thin Films

摘要

Oxygen-containing yttrium hydride, YH_x:O_y, is an inorganic phothochromicmaterial which exhibits promising features for its application in smartwindows, ophthalmic lenses, and many more. In the present work the opticalproperties of photochromic and non-photochromic YH_x:O_y thin films preparedby magnetron sputtering are studied by variable angle ellipsometry andspectrophotometry. These include the study of the complex refractive index,the transmittance, and luminous transmittance, as well as the reflectance ofa selection of samples of diverse structural properties obtained underdifferent deposition conditions. In the case of the photochromic YH_x:O_y thinfilms, the refractive index in the near infrared and visible regions is foundsimilar to the one corresponding to yttrium oxide, Y_2O_3. However, the YHx:O_y films exhibit a smaller band gap and hence higher absorption in the nearultraviolet than Y_2O_3. The photodarkening potential of the films are alsoquantified and characterized by the study and modeling of their opticalproperties before and after illumination. Our results show that photochromicYH_x:O_y films, with a luminous transmittance above 80 % in the clear state,can reduce its transparency up to a 30% after 1 h illumination at 1 Sun.