An advanced color tunable persistent luminescent NaCaGeOF:Tb phosphor for multicolor anti-counterfeiting.

Luminescent materials play an important role in anticounterfeiting applications due to their superior properties of visual convenience and high concealment. However, traditional luminescent materials usually exhibit monochromatic emission and are easily counterfeited. Therefore, in this work, we report a multicolor long persistent luminescence (PersL) material, NaCa2GeO4F:Tb3+ (abbreviated as NCGOF:Tb3+), where the color of PersL can be tuned from blue to cyan and bright green by changing the concentration of Tb3+, and the afterglow (concentration) can last for 5.62 h (0.1%), 8.52 h (0.4%) and 7.14 h (0.8%) at the corresponding concentrations of Tb3+, respectively. Investigation revealed that the multicolor PersL is essentially associated with the opportune traps and cross-relaxation effect of Tb3+ in NCGOF. Based on the unique features of PersL, anticounterfeiting devices have been fabricated, and the results indicate that their multicolor features can be easily detected using a portable ultraviolet lamp, and that they are impossible to counterfeit using any substitute so far, meaning that they provide a high level of security for use in practical applications.