Achieving multicolour and multimodal luminescence in Ca3Al2Ge3O12:Bi3+/Ln3+ (Ln = Tb, Eu, Sm, and Dy) persistent phosphors for multiple applications

Anti-counterfeiting and encryption have become hot topics in information security, however, traditional persistent luminescence (PersL) phosphors face significant challenges in achieving multi-colour anti-counterfeiting and visualization (influenced by ambient light). Here, we propose a novel multimodal anti-counterfeiting strategy based on Ca3Al2Ge3O12:Bi3+/Ln(3+) (Ln = Tb, Eu, Sm, and Dy). There is efficient energy transfer from Bi3+ to Ln(3+) and with increasing the Ln(3+) concentration, the emission can move from blue to green (Ca3Al2Ge3O12:Bi3+,Tb3+), red emission (Ca3Al2Ge3O12:Bi3+,Eu3+), yellow-green emission (Ca3Al2Ge3O12:Bi3+,Dy3+) and orange-red emission (Ca3Al2Ge3O12:Bi3+,Sm3+). In addition, ultraviolet-B (UVB) emission was successfully sustained with an afterglow time (>20 hours). The combination of multi-colour afterglow and the sustained UVB emission in the phosphor enables identification of fingerprints, anti-counterfeiting applications and advanced and secure storage of Morse code, barcodes, American Standard Code for Information Interchange (ASCll) codes, etc. These results indicate that this work provides new perspectives in terms of advanced anti-counterfeiting and optical storage data systems.