Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany.
Light Technology Institute, Karlsruhe Institute of Technology, Engesserstrasse 13, 76131, Karlsruhe, Germany.
Sci Rep. 2022 Feb 8;12(1):2100. doi: 10.1038/s41598-022-05885-6.
A significant impediment to the deployment of anti-counterfeiting technologies is the reliance on specialized hardware. Here, anti-counterfeiting labels are developed that are both excited and detected using a smartphone. The persistent luminescence pattern and color changes on the timescale of hundreds of milliseconds to seconds. The labels can be authenticated by comparing still images from the red and green channels of video acquired at known times after flashlight excitation against expected reference patterns. The labels are based on a green-emitting SrAlO: Eu,Dy (SAED), and red-emitting CaS:Eu phosphors whose lifetimes are varied: (i) for SAED from 0.5 to 11.7 s by annealing the commercial material in air; and (ii) CaS:Eu from 0.1 to 0.6 s by varying the dopant concentration. Examples of anti-counterfeiting labels exhibiting changing emission patterns and colors on a seven-segment display, barcode, and emoji are demonstrated. These results demonstrate that phosphors with visible absorption and tunable persistent luminescence lifetimes on the order of hundreds of milliseconds to seconds are attractive for anti-counterfeiting applications as they allow authentication to be performed using only a smartphone. Further development should allow richer color shifts and enhancement of security by embedding further covert anti-counterfeiting features.
防伪技术的广泛应用面临着一个重大障碍，即对专用硬件的依赖。在此，我们开发了一种防伪标签，它可以使用智能手机进行激发和检测。该标签可以在数百毫秒到数秒的时间内产生持久的发光图案和颜色变化。可以通过将闪光灯激发后已知时间拍摄的视频的红色和绿色通道的静态图像与预期的参考图案进行比较，来对标签进行身份验证。标签基于绿色发射 SrAlO：Eu，Dy（SAED）和红色发射 CaS：Eu 荧光粉，其寿命可通过以下两种方式进行调整：（i）通过在空气中对商用材料进行退火，将 SAED 的寿命从 0.5 秒调整到 11.7 秒；（ii）通过改变掺杂浓度，将 CaS：Eu 的寿命从 0.1 秒调整到 0.6 秒。展示了在七段显示器、条形码和表情符号上具有变化发射图案和颜色的防伪标签示例。这些结果表明，具有可见吸收和可调节的持久发光寿命的荧光粉在数百毫秒到数秒的范围内非常适合防伪应用，因为它们仅使用智能手机就可以进行身份验证。进一步的开发应该能够实现更丰富的色彩变化，并通过嵌入进一步的隐蔽防伪特征来增强安全性。
