Tunable ultraviolet-B full-spectrum delayed luminescence of bismuth-activated phosphors for high-secure data encryption and decryption

• Bi 3+ emission is for the first time tuned controllably and finely within UVB full-spectrum. • UVB persistent luminescence can last more than 72 h. • Tunable UVB optically stimulated luminescence can be repeatedly revitalized by external NIR light. • The application for high-secure data encryption and decryption using 8-bit ASCII binary codes is demonstrated. The ultraviolet-B (UVB) delayed luminescence materials, holding great potential in the field of phototherapy, sterilization, photocatalysis and anti-counterfeiting, however, lack of spectral tunability study and restricted to limited persistent time. In this paper, a series of Bi 3+ -doped garnet phosphors were successfully synthesized and the Bi 3+ emission is for the first time tuned controllably and finely within UVB full-spectrum. The continuous replacement of Ga 3+ by Al 3+ ions gives rise to a fine blue-shift of Bi 3+ emission from 313 to 302 nm due to the greater covalency of the Ga O bond. Driven by the increased symmetry of the dodecahedron, it is further shifted to a much shorter wavelength step-by-step and finally approached to 298 nm with the progressive substitution of Y 3+ by Lu 3+ ions. The developed Bi 3+ -doped phosphors show delayed UVB luminescence, of which the persistent time can be optimized to more than 72 h by the effective combination of bandgap engineering and trap engineering strategies. Moreover, excellent optically stimulated luminescence that the UVB persistent luminescence of the pre-irradiated phosphor can be repeatedly revitalized by a low-energy 870 nm near-infrared (NIR) LED light source. As a proof-of-concept, invisible characters of UV write-in and NIR read-out for high-secure data encryption and decryption application using 8-bit ASCII binary codes were implemented. This work not only offers the path for the development of novel UVB phosphors with desired emission wavelength but also extends the applications of UVB delayed luminescence materials.