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

Abstract

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⁺/Ln³⁺ (Ln = Tb, Eu, Sm, and Dy). There is efficient energy transfer from Bi³⁺ to Ln³⁺ and with increasing the Ln³⁺ 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.