Realizing\nBright−Dark Dual-Field Multimode\nOptical Signals in Photochromic Apatite Phosphors for Security Identification

Regulating defect distribution in\ninorganic phosphors\nis paramount\nfor realizing multimode dual-field optical signals for high security\nlevel identification but remains an ongoing challenge. Here, we propose\na strategy of equivalent anion doping and nonequivalent cation doping\nto successfully regulate the trap distribution and density in Ba<sub>5</sub>(PO<sub>4</sub>)<sub>3</sub>Cl:F<sup>−</sup>,Eu<sup>2+</sup>,Ce<sup>3+</sup> (BPCF-AG) phosphors. Due to the coexistence\nof shallow and deep traps for different photon processes, the BPCF-AG\nexhibits simultaneous photochromism in a bright field and tetramode\nluminescence (photoluminescence, afterglow, 980 nm photostimulated\nluminescence, and 650/532 nm photostimulated afterglow) in a dark\nfield. The trap roles responsible for versatile optical behaviors\nare investigated by thermoluminescence curves, and a reasonable mechanism\nis proposed. In addition, we design a series of demonstrations for\nsecurity identification and information encryption based on the dual-field\nmultimode optical signals of BPCF-AG to illustrate its potential application\nscenarios.