Thermochromic and photochromic colour change in Mg-Ni-H thin films

Mg-Ni-H thin films were deposited by reactive magnetron sputtering. As-deposited samples were Mg-rich and annealed in air by two steps at T=220 and 290 °C in order to increase crystallinity. A reversible, thermochromic effect was detected when the crystalline yellow colour sample underwent a colour transition and changed its colour from yellow to red. The change in transmission spectra of the prepared thin films in visible range of spectra was induced by in situ heating setup. The continuous shifts of the transmission spectra at T=200 °C towards lower band gap was observed. Additionally, a photochromic effect was detected and confirmed by exposing the sample to visible light, as grey-coloured area appeared on the sample.