Photochromism-modulated reversible dual-modal luminescence of CaWO₄:Bi³⁺/Er³⁺ for advanced anti-counterfeiting application

Lanthanide-doped inorganic phosphors with reversible luminescence modulation based on photochromic effect have attracted significant attention in the fields of advanced anti-counterfeiting. However, there are still some challenges in the design of lanthanide-doped materials with both dual-modal emissions (upconversion/ downshifting) and photochromism in response to dual-wavelength light stimulation. Here, in this work, Bi³⁺ co-doped CaWO₄:Er³⁺ phosphor has been successfully prepared, exhibiting reversible photochromism from buff to brown color under alternating stimulation of 254 nm ultraviolet and 473 nm blue lights. Benefiting from its reversible photochromic effect, the dual-modal emissions of Er³⁺-activated CaWO₄ sample can be reversibly modulated under the excitation of 291 nm ultraviolet light or 980 nm laser. Consequently, the photochromism-induced real-time luminescent modulation feature enables the practical applications of the developed phosphors in high-level anti-counterfeiting.