“…Photochromic species generally show reversible color change upon external stimuli. [2] If X-rays behave as a stimulus, they are ideal candidates of such materials because they are recyclable.There have been some excellent studies on X-ray-induced photochromic materials, like Prussian blue analogs, [3] Fe II spin-crossover complexes, [4] manganite, [5] spinel, [6] cobalt dioxolene, [7] zinc phosphate with methylviologen cations, [8] BiOI/BiI-nylon11 composite films, [9] and oxometallates with impurities (such as LiNbO 3 :Cu), [10] in strict accordance with the definition of photochromism. [2] However, to the best of our knowledge, examples of X-ray-induced photochromic materials are still rather rare in the literature.…”