Designing X-ray-Excited UVC Persistent Luminescent Material via Band Gap Engineering and Its Application to Anti-Counterfeiting and Information Encryption

Persistent luminescent materials (PLMs) are promising candidates for the anti-counterfeiting and information encryption field. However, ultraviolet (UV) excitation and visible emission are partially responsible for enabling information that has been encrypted to combat counterfeiting to be accessed by trial and error, resulting in imitation and information leakage. Here, we propose the possibility of controlling the persistent luminescent (PersL) emission spectra and its excitation light source with the use of band gap engineering, while obtaining X-ray exciting, not UV exciting UV PLM for advanced anti-counterfeiting and encryption application. Cationic substitution was used to adjust the width of the band gap of Lu(X)O4 (X = V, Nb, Ta, and P) from ∼4 to 9 eV. In addition, Bi3+ was introduced into the host as an emitter, which enabled the PersL emission spectra to be modulated from ∼550 to 230 nm. Among these PLMs, LuPO4:Bi3+ has unique optical properties. Under UV excitation, LuPO4:Bi3+ exhibits weak, inconspicuous visible down-conversion luminescence (DCL), without PersL ceasing once excitation is discontinued. Interestingly, LuPO4:Bi3+ displays UV PersL after X-ray excitation, and human eyes are insensitive to UV PersL, which requires specialized optical equipment to detect. A proof-of-concept assessment of LuPO4:Bi3+ for anti-counterfeiting and information encryption applications demonstrated its suitability in this regard.