Highly flexible dual-mode anti-counterfeiting designs based on tunable multi-band emissions and afterglow from chromium-doped aluminates

Abstract

Fluorescent materials generally show diverse light emission, simple manufacturing processes, long service life, and long-term reliability properties, and they have gradually become a hotspot in the field of anti-counterfeiting. Phosphors with multi-functions for the realization of dual-mode anti-counterfeiting designs are still subject to the tailoring difficulty, readout order restriction, detection complexity, etc. To solve these problems, we propose a new flexible dual-mode anti-counterfeiting design by using a series of phosphors MAl₁₂O₁₉:Cr³⁺ (M = Ca and Sr) based on their both deep red/NIR dual emissions and afterglow. By tailoring the concentration of dopants, a similar deep red but strong NIR intensity comparison has been realized. In the fluorescent mode, the intense NIR emission that represents the effective information can be pictured by filtering the deep red encryption light under white LED. In addition, the persistent luminescence in the afterglow mode, which has been tuned by Ti⁴⁺ co-dopants, can be pictured after UV irradiation. The dual-mode information can be designed separately and detected independently without interference or readout order restriction. Such a dual-mode system with flexibility and simplicity properties is a good choice not only for anti-counterfeiting but also for the multi-layer information encryption.