Optical indices of switchable mirrors based on Mg–Y alloy thin films in the transparent state

Abstract To improve the visible transmittance of switchable mirrors based on Mg–Y alloys in the transparent state using antireflection layers, optical indices n and κ of the hydrogenated switchable mirrors were evaluated using spectroscopic ellipsometry in the range of 310 to 1650 nm. The Y composition z in the Mg 1 −  z Y z alloys was varied between 0.51 and 0.7. The evaluated spectra both n and κ in the visible range increased with decreasing wavelength and increasing Y composition. Furthermore, the wavelength where the k value increased sharply was increased with Y composition. As a result of estimation of the effect of antireflection (AR) coating, it is expected that a switchable mirror using Mg 0.39 Y 0.61 covered with AR layer with the refractive index of ~ 2.3 and ~ 50 nm thickness improved to be T vis of over 60%, while the switchable mirror without AR had T vis of 34%. Thus, it is concluded that AR layer is effective to improve T vis in the transparent state.