Enhancing the photochromic properties of Bi 2 O 3 through sintering and lanthanide doping for optical security applications

Abstract High‐performance photochromic luminescent inorganic materials have garnered significant attention in optical storage and security; however, they often feature complex chemical compositions. Herein, the photochromic properties of the Bi 2 O 3 are investigated, exhibiting a color change from yellow to light brown upon 365 nm flashlight stimulation. The coloration contrast of the Bi 2 O 3 can be enhanced by sintering at 650°C and doping with 1% Er 3+ ions, resulting in an increase in coloration contrast from 13.2% to 28.5%. This is mainly due to the calcination and lanthanides doping‐induced increase in the proportion of oxygen vacancy in the α‐Bi 2 O 3 lattice. The reversible modulation of Er 3+ upconversion luminescence, achieved through combined re‐absorption and energy transfer mechanisms, demonstrates promising applications in optical anti‐counterfeiting systems