Effect of temperature and illumination conditions on the photochromic performance of yttrium oxyhydride thin films

Transparent yttrium oxyhydride (YHO) thin films exhibit photochromic effects under ambient conditions. The optical transmission in such materials can be strongly modulated upon light absorption. This switchable optical property is interesting for technological applications, such as energy-saving smart windows and optical sensors. For the practical use of photochromic YHO materials, it is crucial to understand how the kinetics of coloration and the resulting photochromic contrast are influenced under different illumination conditions at both room and elevated temperatures. In the present study, we have prepared yellow, transparent, photochromic YHO thin films on glass substrates by using reactive magnetron sputtering. We investigated the photochromic performance of both as-deposited and annealed YHO thin films using illumination sources with varying photon energies and intensities. The photochromic contrast and the coloration were found to decrease considerably with increasing annealing temperature and with decreasing intensity and photon energy of the illumination sources. Moreover, time-resolved optical transmission measurements revealed a nearly logarithmic time dependence of the coloration of YHO thin films, indicating rapid coloration in the beginning of light exposure, followed by slow coloration with increasing illumination time.