Photo-reversible color-switching system using solar-driven additive-free oxygen vacancies-rich bismuth oxychlorobromide nanoflowers

Inorganic metal-oxide semiconductors have advantages over organic counterparts in applications like rewritable media due to their cost-effectiveness and stability. However, they encounter challenges such as limited photo-response to UV irradiation only, reversibility under ambient conditions, and complex production processes. To overcome these issues, we created additive-free inorganic nanoflower-like films of bismuth oxychlorobromide (BiOCl_0.8Br_0.2) that can change color reversibly. Our research demonstrates that these films transition gradually from white to black in approximately 10 min under natural sunlight, enabling information storage for up to 48 h before returning to white. By heating to 80 °C, the reversal process can be shortened to 12 min, and the films maintain their quality during 15 writing-erasing cycles. Analysis revealed the presence of hydroxyl groups and oxygen vacancies (OVs) on the film surface. These OVs act as electron traps, enhancing the generation of electrons and holes, and expediting the coloration process. Removing the light source prompts the OVs to oxidize water molecules, restoring the original white color and erasing the stored information. The photo-reversible color-switching system created using these materials exhibits excellent reversibility, effectively responding to light for writing and ambient conditions for information removal. This cost-effective approach yields highly stable, responsive, and reversible BiOCl_0.8Br_0.2 nanoflowers, opening new opportunities for dye-free photochromic materials in various color-switching applications. Compared to alternative photochromic materials, this system's simplicity of preparation showcases promising progress in the development of dye-free photochromic materials.