Reversible multiplexing optical information storage and photoluminescence switching in Eu2+-doped fluorophosphate-based tunable photochromic materials

Materials exhibiting luminescent switching upon photochromic reaction have received increasing attention due to their potential applications in erasable optical storage. Nevertheless, it is still challenging to synthesize photochromic materials that selectively absorb different wavelengths of light for erasable optical storage. Herein, we report a series of fluorophosphate structure (Ca,Sr,Ba)5(PO4)3F:Eu2+ photochromic materials with tunable absorption bands upon photochromic reaction. Tunable photochromism is a phenomenon is rarely observed in inorganic materials. Thus, to fill this gap, we designed (Ca,Sr,Ba)5(PO4)3F:Eu2+ photochromic materials with highly reversible tunable photochromism by adjusting and substituting the alkaline-earth metal. The substitution of the divalent cations with a smaller ionic radius by larger cations induced a shift in the absorption band of the (Ca,Sr,Ba)5(PO4)3F:Eu2+ photochromic material to a longer wavelength. The multicolor change may pave the way for the design of photochromic materials to meet specific application requirements. All as-prepared photochromic flexible films showed excellent fatigue resistance, water resistance, flexibility and stretchability. Writing, erasing, and reading were performed using the flexible photochromic films, demonstrating their particular application in complicated environments for optical storage and rewritable flexible devices. An efficient energy transfer process was established between luminescent and photochromic units, which may open a door for the design of high-performance optical storage materials. Erasable optical storage could be excited by UV and visible light to encode and decode on the flexible film.