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 Bi3+-doped garnet phosphors were successfully synthesized and the Bi3+ emission is for the first time tuned controllably and finely within UVB full-spectrum. The continuous replacement of Ga3+ by Al3+ ions gives rise to a fine blue-shift of Bi3+ emission from 313 to 302 nm due to the greater covalency of the GaO 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 Y3+ by Lu3+ ions. The developed Bi3+-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.